CA II, a potential biomarker by proteomic analysis, exerts significant inhibitory effect on the growth of colorectal cancer cells

  • Authors: Rui Zhou, Wenjun Huang, Yuqin Yao, Yuxi Wang, Ziqiang Li, Bin Shao, Jian Zhong, Minghai Tang, Shufang Liang, Xia Zhao, Aiping Tong, Jinliang Yang
  • View Affiliations

  • Published online on: Friday, May 31, 2013
  • Pages: 611-621
  • DOI: 10.3892/ijo.2013.1972

Abstract

In the Western world, colorectal cancer (CRC) is the third most common cancer with poor prognosis. To identify the proteins and to elucidate the possible mechanisms involved in colorectal carcinogenesis, 2-DE coupled with MS/MS analysis were employed to compare the global protein profile between CRC and individual matched normal tissues from 8 CRC patients. Of 36 proteins identified, carbonic anhydrase II (CA II) was one of most significantly altered and its downregulation in CRC tissues was verified by RT-PCR, western blotting and immunohistochemistry methods, suggesting that CA II may serve as a potential biomarker for CRC diagnosis. To investigate the function and mechanisms of CA II in CRC, a stable SW480 colorectal cancer cell line overexpressing CA II was established. It was shown that overexpression of CA II remarkably suppressed tumor cell growth both in vitro and in vivo, which was in part interpreted by cell cycle arrest at G0/G1 and G2 phase. Further mechanism analysis revealed that the sensitivity of colorectal cancer cells to chemotherapy drugs could be increased by CA II overexpression. Taken together, these data suggest that CA II may be a potential biomarker for early diagnosis of CRC and the results may contribute to a better understanding of the molecular mechanism of CRC and colorectal cancer treatment.

Introduction

Colorectal cancer (CRC) is a major international health problem that is the third most frequent type of cancer and the second most common cause of cancer related death in the Western world (1). It has been reported that when CRC is diagnosed at early stage, nearly 90% of the patients can be cured by surgery. However, this disease is very often diagnosed at an advanced stage, resulting in poor prognosis subsequently (24). In addition, the mechanisms of CRC development and progression are not quite clear and have yet to be further explored. Therefore, more insight and new methods to investigate the underlying mechanisms of CRC are needed to identify effective biomarkers and this is critical for proper control of CRC.

In recent years, proteomics have burst onto the scientific scene rapidly (5). Based on 2-DE and mass spectrometry, hundreds of proteins can be identified simultaneously and precisely through high-throughput identification. Therefore, proteomics have been widely applied to search for diagnostic biomarkers in early disease detection, as well as mechanism analysis of disease, especially in the field of cancer research (68). In the present study, differentially expressed proteins between individually matched CRC and normal tissues were profiled from 8 CRC patients. Of 36 proteins identified, carbonic anhydrase II (CA II) was chosen for verification and function and mechanism analysis. It was expected that the results from the study may contribute to a better understanding of the molecular mechanism of CRC and provide insight into colorectal cancer treatment.

Materials and methods

Patients and tissue preparation

For proteomic analysis, 8 cases of CRC and pared adjacent normal tissues were obtained from West China Hospital, Sichuan University. The clinical characteristics of the patients are summarized in Table I. Fresh tissues samples were obtained immediately after the surgery, snap-frozen immediately in liquid nitrogen and then stored at −80°C before analysis. For the validation studies, 25 cases of paraffin-embedded primary CRC tissues and pared adjacent normal tissues were collected consecutively from patients at West China Hospital in 2009. Written informed consent was obtained from all patients and the study procedures were approved by the Scientific and Ethics Committee of Sichuan University (Chengdu, China).

Table I.

Clinical features of all human tissue samples.

Table I.

Clinical features of all human tissue samples.

SampleAgeGenderLocationaUICC staging
184MaleAI
253MaleRIII
366MaleAII
472MaleDIII
559FemaleTIII
679MaleSII
760FemaleRIII
857MaleRII

a A, ascending colon; T, transverse colon; D, descending colon; S, sigmoid colon; R, rectum.

Proteomic analysis and protein identification

2-DE was carried out as previously described (9) with minor modifications. Briefly, tissue sample was ground into powder in liquid nitrogen and sonicated in lysis buffer (7 M urea, 2 M thiourea, 4% CHAPS, 65 mM DTT, 0.2% ampholyte pH 3.0–10.0; Bio-Rad, Hercules, CA, USA) containing protease inhibitor cocktail. IPG strips loaded with 1 mg protein (17 cm, pH 3.0–10.0, non-linear; Bio-Rad) were passively rehydrated for 12–16 h. Having been separated according to their pI for the first dimension, the strips were transferred to the second dimension 12% SDS-PAGE for the separation according to the molecular weight. Spots that showed consistent and significant differences (>2-fold) were selected for mass spectrometry (MS) analysis.

In-gel digestion of protein was conducted using MS-grade Trypsin Gold (Promega, Madison, WI, USA) by following the manufacturer’s instructions. ESI-Q-TOF MS/MS analysis and protein identification were performed as described in our previous proteomic studies (9). Briefly, peptide mass maps were acquired using a Q-TOF mass spectrometer (Micromass, Manchester, UK) fitted with an ESI source. For MASCOT analysis, peptide and fragment mass tolerance were set at 0.1 and 0.05 Da, respectively.

Semiquantitative RT-PCR

Total RNA extraction was performed using TRIzol reagent (Invitrogen). cDNA was then synthesized using the ExScript™ reagent kit (Takara, Shiga, Japan) following the manufacturer’s instructions. The primer sequences and the expected sizes for PCR products were as follows: CA II, 5′-GTCCCATAGTCTGTATCCAA-3′ (sense) and 5′-GAGTGCTCATCACCCTACAT-3′ (antisense) (301 bp); GAPDH, 5′-TGGAAGGACTCATGACCACA-3′ (sense) and 5′-GCTTCCCACCTTCTTGATG-3′ (antisense) (280 bp). The amplification parameters consisted of 25 (CA II) or 20 cycles (GAPDH) at 94°C for 30 sec, 60°C (CA II) or 57°C (GAPDH) for 30 sec and 72°C for 30 sec. The PCR products were analyzed by electrophoresis in 1.2% agarose gels and visualized by Gold View (Takara) staining.

Western blotting

CRC tissues and cells were lysed with cold RIPA lysis buffer containing protease inhibitors. Thirty micrograms of protein extraction were applied to 12% SDS-PAGE gels and then transferred to polyvinylidene fluoride membrane. The membrane was probed with primary antibodies against CA II (1:1,000, GeneTex), E-cadherin (1:1,000, Cell Signaling Technology, MA, USA), vimentin (1:1,000, Cell Signaling Technology), PKM2 (1:1,000, Cell Signaling Technology) and GAPDH (1:1,000, Santa Cruz Biotechnology, Inc. Santa Cruz, CA, USA), respectively. Blots were developed with HRP-conjugated secondary antibodies (1:5,000, Santa Cruz) and chemiluminescent substrate (Millipore, MA, USA) on Kodak X-ray film.

Immunohistochemistry and immunocytochemistry

Tissue slides or SW480 cells fixed in polystyrene culture were stained with the rabbit anti-human CA II antibody (diluted 1:200, GeneTex) using the DAB substrate solution according to the manufacturer’s instructions.

Cell culture and establishment of a stable cell line

Four human colorectal cancer cell lines, SW480, SW620, HCT116 and LoVo cell were purchased from ATCC (American Type Culture Collection, Manassas, VA, USA). Cells were grown in DMEM medium (Gibco, Carlsbad, CA, USA) supplemented with 2 mM L-glutamine, 10% FBS, 100 U/ml penicillin and 100 μg/ml streptomycin. Cells were maintained in a humidified environment containing 5% CO2 at 37°C.

For establishment of the stable cell line SW480, cells were transfected with DNA constructs (OriGene) encoding EGFP-CA II (SW480-CA II-over) or EGFP (SW480-control). Forty-eight hours after transfection, cells are harvested, diluted (1:10) and plated in fresh medium containing G418 (800 μg/ml, Invitrogen, Carlsbad, CA, USA). Colonies with green fluorescent signal were then picked and expanded.

Drug treatments and MTT assay

Tumor cells were seeded in 96-well plates at 5×103 cells per well. After 16 h, cells were incubated with various concentrations of drugs. SW480 cells were treated with different concentration of oxaliplatin (10, 20, 30, 40 and 50 μM respectively, Sigma, St. Louis, MO, USA); and, after pretreatment with 100 μM acetazolamide (Sigma) for 8 h, HCT116 cells were treated with oxaliplatin as in SW480 cells. Forty-eight hours later, the effects of drugs on cells were assessed using MTT methods. Briefly, cells were incubated with 20 μl of MTT reagent (20 mg/ml) for 4 h, followed by addition of 100 μl of solubilization solution into each well. The plates were left in the dark room overnight and optical density (OD) was measured at 590 nm wavelength. Results are expressed as percentage of viable cells compared with untreated cells (with 100% viability). The results are based on three independent experiments. Drug concentrations that inhibit 50% of cell viability (IC50) for oxaliplatin were determined using the method described previously (10).

Colony formation assay

SW480 cells overexpressing CA II and control cells were seeded at 300 cells/well in a 6-well plate with triplicate wells for each group. After 14 days of culture, cells were fixed in methanol for 30 min and stained with Giemsa (Beyotime). The number of clones consisting of >50 cells was counted. The colony forming efficiency was calculated according to the formula: (the clone number/the plated cell number) × 100.

Flow cytometry

The cells were harvested, washed twice with PBS and fixed in 70% ethanol overnight. After incubation with RNAse A and propidium iodide (Beyotime) for 30 min at 4°C in the dark, cell cycle data were collected on a flow cytometer with a 488-nm laser and analyzed with the manufacturer’s software.

Statistical analyses

All quantitative data were expressed as mean ± SD. Comparisons between two groups were performed by Student’s t-test. Statistical calculations were performed with SPSS 11.0.0 statistical software. Data were considered as statistically significant at P<0.05.

Results

Identification of differentially expressed proteins between CRC and the corresponding normal tissues

The proteome of individual-matched CRC and normal colorectal tissues from 8 patients (mean age 66.25±10.39 years; range 53–84 years) were compared by 2-dimensional gel electrophoresis (2-DE) using a broad pH gradient (pH 3.0–10.0 non-linear). Coomassie staining of 2-D gels visualized 852±46 and 871±34 protein spots within normal colorectal tissues and CRC, respectively. Representative 2-DE maps are showed in Fig. 1A and spot no. 13 (boxed in Fig. 1A) as a selected example, was significantly downregulated in CRC as shown in enlarged form in Fig. 1B. As a result, 52 spots showed >2.0-fold change (P<0.05). Differentially expressed protein spots were subsequently subjected to MS/MS analysis. Of 52 spots, 44 spots corresponding to 36 unique proteins were identified probably due to post-translational modification such as protein phosphorylation (Table II). Notably, carbonic anhydrase II (CA II) corresponding to spot no. 13 (Fig. 1B) was found to be one of the most significantly differential expression between cancer and normal tissues. It was downregulated >5-fold in CRC compared with the normal tissues. The mass spectra of CA II is shown in Fig. 2. MS/MS analysis of CA II revealed 8 matched-peptides, 50% sequence coverage and a MOWSE score of 226. Due to the confident identification, CA II was chosen as the subsequent focus of this study.

Table II.

Identified proteins by MS/MS analysis.

Table II.

Identified proteins by MS/MS analysis.

Protein descriptionGene nameFunctionAccession no.Theoretical Mr/pIaScorebNo. of pepc (%)Fold-changed (mean ± SD)
1Protein disulfide-isomerase A3PDIA3Protein foldingP3010157146/5.9838812/28↓2.1±0.7
2 Hydroxymethylglutaryl-CoA synthase, mitochondrialHMCS2Energy metabolismP5486857113/8.402287/29↓2.4±0.6
3Isocitrate dehydrogenase [NADP] cytoplasmicIDHCEnergy metabolismO7587446915/6.5326310/41↓2.2±0.7
4Leukocyte elastase inhibitorILEUProteolysisP3074042829/5.9020512/41↓3.2±0.9
5Sialic acid synthaseSIASGlucose metabolismQ9NR4540738/6.291967/37↓2.2±0.4
6Creatine kinase U-type, mitochondrialKCRUMetabolismP1253247406/8.605199/41↓2.0±0.6
7Poly(rC)-binding protein 1PCBP1RNA bindingQ1536537987/6.6625110/54↓2.3±0.8
8Ribose-phosphate pyrophosphokinase 2PRPS2Nucleic acid metabolismP1190835146/6.151916/30↓2.2±0.8
9 Hydroxyacyl-coenzyme A dehydrogenase, mitochondrialHCDHEnergy metabolismQ1683634313/8.882186/39↓3.1±0.7
10Sulfotransferase family cytosolic 1B member 1ST1B1Protein modificationO4370435048/6.57641/4↓4.2±0.9
11Sulfotransferase 1A1ST1A1Protein modificationP5022534289/6.1630411/51↓3.6±1.1
12Carbonic anhydrase 1CAH1Carbonate dehydrataseP0091528909/6.59113010/61↓2.5±0.8
13Carbonic anhydrase 2CAH2Carbonate dehydrataseP0091829285/6.872268/50↓5.6±1.5
14Rho GDP-dissociation inhibitor 1GDIR1GTPase activatorP5256523250/5.027939/57↓2.4±0.6
15Protein ETHE1, mitochondrialETHE1Energy metabolismO9557128368/6.3587511/74↓1.6±0.4
16Cytochrome b-c1 complex subunit Rieske, mitochondrialUCRIElectron transportP4798529934/8.552726/29↓2.3±0.9
17 Translationally-controlled tumor proteinTCTPCalcium ion bindingP1369319697/4.841295/36↓2.9±0.8
18NADH dehydrogenase [ubiquinone] iron-sulfur protein 8, mitochondrialNDUS8Energy metabolismO0021724203/6.002876/32↓2.2±0.6
19Superoxide dismutase [Mn], mitochondrialSODMRedox regulationP0417924878/8.357039/71↓2.4±0.8
20 Phosphatidylethanolamine-binding protein 1PEBP1ATP bindingP3008621158/7.01127611/76↓N/A e
21Plasma cell-induced resident endoplasmic reticulum proteinPERP1Protein bindingQ8WU3921023/5.373975/55↓2.1±0.6
22Anterior gradient protein 2 homologAGR2Protein bindingO9599420024/9.034629/42↓2.3±0.7
23Anterior gradient protein 2 homologAGR2Protein bindingO9599420024/9.032799/42↓3.4±0.6
24Cytochrome c oxidase subunit 5B, mitochondrialCOX5BElectron transportP1060613915/9.07472/19↓2.4±0.8
25Cytochrome b-c1 complex subunit 7QCR7Electron transportP1492713522/8.731123/34↓2.1±0.8
26Fatty acid-binding protein, liverFABPLLipid metabolismP0714814256/6.603679/61↓3.0±0.9
27Fatty acid-binding protein, liverFABPLLipid metabolismP0714814256/6.60672/33↓3.6±1.3
28D-dopachrome decarboxylaseDOPDProtein modificationP3004612818/6.711455/44↓2.2±0.7
29Myosin-11MYH11Muscle contractionP35749228054/5.42682/2↑N/A
30ATP synthase subunit d, mitochondrialATP5HMetabolismO7594718537/5.211164/43↑2.6±0.5
31Triosephosphate isomeraseTPISGlucose metabolismP6017426938/6.451607/41↑2.3±0.6
32TransgelinTAGLActin bindingQ0199522653/8.8785813/59↑N/A
33TransgelinTAGLActin bindingQ0199522653/8.87142815/55↑N/A
34TransgelinTAGLActin bindingQ0199522653/8.8748711/64↑2.2±0.7
35Transgelin-2TAGL2Not determinedP3780222548/8.4164016/67↑2.3±0.7
36Actin-related protein 2/3 complex subunit 5-like proteinARP5LStructural componentQ9BPX516931/6.15841/16↑2.2±0.7
37TransgelinTAGLActin bindingQ0199522653/8.871847/43↑3.3±0.7
38TransgelinTAGLActin bindingQ0199522653/8.8748711/64↑N/A
39TransgelinTAGLActin bindingQ0199522653/8.8732610/52↑N/A
40TransgelinTAGLActin bindingQ0199522653/8.8710210/52↑3.3±0.9
41TransgelinTAGLActin bindingQ0199522653/8.873266/55↑4.3±1.3
42TransthyretinTTHYThyroid hormone-bindingP0276615991/5.524236/55↑N/A
43Protein S100-A9S10A9Calcium ion bindingP0670213291/5.711004/49↑2.3±0.7
44Eosinophil lysophospholipaseLPPLLipid metabolismQ0531516584/6.82423/25↑2.0±0.9

a Theoretical molecular weight (kDa) and pI from the ExPASy database.

b Probability-based MASCOT scores.

c The number of unique peptides identified by MS/MS sequencing (multiple matches to peptide with the same primary sequence count as one).

d Average expression level (fold-change) in CRC group compared with ad from all analyses (↑, increase; ↓, decrease).

e N/A, not applicable because the spots on one of the paired gels were too weak or non-detectable.

Validation of CA II by semiquantitative RT-PCR and western blot analysis

To confirm the differential expression of CA II between CRC and corresponding normal tissues, validation experiments were performed by RT-PCR and western blot analysis at mRNA and protein level, respectively. The result of RT-PCR analysis showed significantly different mRNA level of CA II between CRC and normal tissues (cancer tissues, 0.31±0.07; normal tissues, 0.98±0.25; Student’s t-test, P<0.01) (Fig. 3A). Western blot analysis was performed using anti-CA II antibody and remarkable CA II downregulation was observed in CRC tissues (cancer tissues, 0.22±0.05; normal tissues, 0.85±0.28; Student’s t-test, P<0.01) (Fig. 3B). Taken together, our data demonstrated that CA II expression notably decreased in CRC compared with normal tissues, which was consistent with the results of 2-DE.

Further verification of CA II expression by immunohistochemistry

To further confirm the reduction of CA II expression in CRC, 25 paraffin-embedded individual-matched CRC and normal colorectal tissues were stained using anti-human CA II antibody. Strong positive staining for CA II mainly located in the cytoplasm and nucleus of epithelium and gland cells in normal colorectal tissues. In contrast, there were weakly or negative staining signal in CRC tissues (Fig. 3C). As shown in Table III significant differences in staining intensity and positive cells were observed between CRC and normal colorectal specimens (rank-sum test, P<0.05). The semiquantitative scoring of immunoreactivity for normal tissues and CRC was 6.45±2.84, 1.57±0.86, respectively (Student’s t-test, P<0.01), suggesting the expression of CA II had a decreased tendency in both frequency and intensity from normal tissues to CRC.

Table III.

The expression of carbonic anhydrase II in colorectal cancer tissues.

Table III.

The expression of carbonic anhydrase II in colorectal cancer tissues.

No.++++++aTotal scoreAverage scoreb
AN25020% (5/25)32% (8/25)48% (12/25)1616.45±.84
Ca2552% (13/25)28% (7/25)20% (5/25)0391.57±0.86

a Rank-sum test, P<0.05;

b Student’s t-test, P<0.01. AN, adjacent normal tissue; Ca, cancer tissue.

CA II overexpression exerts inhibitory effect on CRC cell growth both in vitro and in vivo

In order to investigate the function of CA II in colorectal carcinoma, CRC cancer cell line SW480 was used to establish a stable cell line overexpressing CA II (SW480-CA II-over), since CA II was not detected in SW480 cells (Fig. 4A). Western blot and immunocytochemistry analysis showed that in contrast with no expression in control stable cell line (SW480-control), remarkable expression of CA II was observed in SW480-CA II-over stable cell line (Fig. 4A and B), suggesting successful establishment of stable SW480-CA II-over cell line.

To examine the effect of on CRC cells, MTT assay was carried out. As shown in Fig. 5A, CA II overexpression notably suppressed SW480 cell viability in a time-dependent manner. Colony formation assay showed that overexpression of CA II in SW480 cell significantly suppressed colony formation efficiency compared with control cells (Fig. 5B). Further flow cytometry analysis demonstrated that SW480 cells stably and highly expressing CA II were stalled at G0/G1 and G2 phase with subsequent decrease in S phase compared with control stable cell line (Fig. 5C).

Moreover, the inhibitory effects on CRC cancer cell growth were examined in an animal model. Tumor growth curve drawn based on the data from in vivo tumor model showed that SW480 overexpressing CA II had a slowed growth rate (Fig. 5D). Representative images of tumor dissection showed that high expression of CA II in tumor cell resulted in suppressed tumor volume (Fig. 5E). As shown in Fig. 5F, there was a remarkable difference in average tumor weight between CA II-overexpression and control group (CA II-over, 301.3±120.7 mg; control, 730±240.5 mg; Student’s t-test, P<0.01). Our results in vitro and in vivo suggested that CA II could serve as a tumor suppressor gene and suppress colorectal carcinoma growth and development.

Cytotoxicity assay suggests CA II increases the sensitivity of CRC cells to oxaliplatin

Through catalyzing the reversible reactions of CO2 and water: CO2 + H2O⇆H+ + HCO3, CA II exerts an important role in acid-base balance in living organism. Thus, it was hypothesized that some signal pathways underling tumor development might be regulated by CA II. As a rate-limiting enzyme of aerobic glycolysis in tumor, embryonic M2 isoform of pyruvate kinase (PKM2) was first determined by western blotting. Similar protein level of PKM2 was observed in control and SW480-CA II-over cells (Fig. 6A); there was no significant difference of PKM2 expression in CRC and corresponding normal tissues (Fig. 6B). E-cadherin and vimentin, two markers corresponding to epithelial and mesenchymal cells, respectively, in epithelial-mesenchymal transition (EMT) were then examined. As shown in Fig. 6A and B, both in vitro cells and CRC tissues, no differential expression of CA II was observed.

Since extracellular acidification of cancer cells in tumor tissues leading to decreased anticancer drug uptake is one of drug-resistance mechanism, it was hypothesized that through pH regulation, CA II may affect sensitivity of CRC cancer cells to anticancer drug. Chemosensitivity tests by MTT showed that CA II overexpression increased the sensitivity of SW480 cells to oxaliplatin (IC50), from 20.5±4.3 μM in control group to 11±5.5 μM (Student’s t-test, P<0.05). In contrast, for HCT116 cells with high expression of CA II, with or without pretreatment with acetazolamide, a non-specific antagonist against CA II, the corresponding IC50 for oxaliplatin was 30.3±3.2 and 23±4.1 μM, respectively (P<0.05), suggesting CA II could induce the chemotherapeutic sensitivity of colon cancer cells.

Discussion

In the Western world colorectal cancer (CRC) is the third most frequent type of cancer and the second most common cause of cancer related death (1). Clearly, early diagnosis and prognosis are urgent for efficient control of CRC and this largely dependents on more advances in the knowledge of mechanisms associated with CRC. In the present study, we compared the proteome between CRC and corresponding normal tissues with 2-DE and MS/MS-based approach. Thirty-six differentially expressed proteins were identified between two groups and most of these proteins were involved in fundamental biological processes. Among these 36 proteins, CA II was further studied according to the following selection criteria: i) it is one of the most significantly and differentially expressed proteins between CRC and matched normal tissues; ii) good reliability of the MS identification of protein; iii) evolutionarily conserved sequence and physiological function is crucial; iv) no or few studies reported the function and mechanism in tumor.

Carbonic anhydrase II (CA II), one of CA family isozymes, catalyzes the reversible hydration of carbon dioxide: CO2 + H2O⇆H+ + HCO3, which is involved in many critical physiological or biochemical processes based on ion transport and pH balance such as respiration, digestion, bone resorption and renal acidification (11). In addition to physiological function, it has recently been found that CA II is abnormally expressed in many types of human cancer. It was noteworthy that there was no consistent expression profile of CA II in different types of cancer tissues (1215). Moreover, there is a contradictory correlation between CA II and the prognosis, progression of cancer patient among different types of cancer (1215). It was shown that CA II was overexpressed in most gastrointestinal stromal tumors and strong staining of CA II indicated significantly better survival rates, suggesting CA II may serve as a diagnostic and prognostic biomarker for gastrointestinal stromal tumors (12). In contrast, immunostaining of the tumors and normal tissues from melanoma, esophageal, renal and lung cancers revealed that CA II was expressed in the tumor vessel while not in normal vessel endothelium (13). Furthermore, compared with negative staining, positive staining of CA II in vessel endothelial cells from meningiomas and glial tumors predicted worse survival rates (14,15). In our study, comparative proteomic analysis showed expression of CA II notably decreased in CRC compared to normal colorectal tissues. RT-PCR, western blot analyses and immunohistochemistry were further performed to validate downregulation of CA II in CRC tissues and these results were also consistent with previous studies that paralleled with increasing severity of colorectal tissue lesions and progression of CRC, the staining intensity of CA II among normal tissues, benign lesions and malignant lesions revealed clearly decreased tendency (1618). However, function and mechanism of CA II in the CRC development and progression have not been investigated.

Considering that CA II expressed is low in CRC tissues, gain of function strategy was utilized to study function of CA II in CRC. Stable cell line overexpressing CA II, SW480-CA II-over was then established given that CA II could not be examined in colorectal cancer cell line SW480. Serial in vitro as well as in vivo experiment results demonstrated that overexpressing CA II significantly suppressed colorectal cancer cell SW480 proliferation both in vitro and in vivo, which could be partially explained by remarkable cell cycle arrest at G0/G1 and G2 phase. To our knowledge, there is no report on how CA II functions in cancer development and progression, in spite of its abnormal expression in many types of cancer. We report that at least in colorectal cancer, CA II may play a role as tumor suppressor gene in cancer development and progression.

A distinguishing phenotype of acidic extracellular pH (pHe) and alkaline intracellar pH (pHi) in solid tumors appears to give selective advantage for tumor growth and development (19). Since carbonic anhydrase isoenzymes were involved in generating acidic tumor microenvironment (20,21), we hypothesized that CA II may also influence the processes associated with tumor microenvironment. Embryonic M2 isoform of pyruvate kinase (PKM2) was first determined by western blotting since it is a rate-limiting enzyme of aerobic glycolysis in tumors and this is specific to metabolism of solid tumors originally described by Otto Warburg (22,23). Overexpressing CA II failed to alter PKM2 protein level and there was no significant change of CA II between matched CRC and normal tissues. Epithelial-tomesenchymal transition (EMT) is a transdifferentiation shift in which epithelial cells lose adhesiveness and polarity and acquire spindle morphology and migratory capacity characteristic of fibroblasts (24,25). It has been shown that EMT plays crucial roles in acquisition of tumoral invasiveness, the initial step of the metastatic cascade in cancer (24,25). Differently expressed E-cadherin and vimentin, two markers corresponding to epithelial and mesenchymal cells, respectively, were not observed in vitro or in tissues. Changed tumor microenvironment can influence the uptake of anticancer drugs and modulate the response of tumor cells to anticancer drugs (19). In the present study, overexpression of CA II decreased the oxaliplatin IC50 compared with that in control SW480 cells. In contrast, in HCT16 cells with high CA II expression, oxaliplatin IC50 increased after pretreatment with CA II antagonist, which suggested that CA II could increase the sensitivity of colorectal cancer cells to chemotherapy drugs. Inconsistent with our results, Mallory et al (26) found that in highly tumorigenic MDA-MB-231 breast cancer cells, knockdown of CA II expression using RNAi strategy resulted in less IC50 than in control cells for doxorubicin, an antineoplastic drug, implicating that CA II may negatively regulate sensitivity of breast cancer cells to chemotherapy drugs. In order to explain this contradiction and get more precise results, it is obviously necessary to increase the number of cell types and chemotherapy drugs for IC50 determination.

In the present study, we only utilized gain of function strategy to study the functions of CA II. Through establishing the colorectal cancer cell line stably overexpressing CA II, we concluded that CA II might serve as a tumor suppressor gene in at least CRC development and progression. In future research, it is necessary to further strengthen our conclusion by using loss of function strategies such as knockout or knockdown of CA II gene expression. Another limitation is the mechanism by which CA II suppressed the development and progression of CRC has yet to be thoroughly revealed, although it was shown that CA II could increase the sensitivity of CRC cells to anticancer drugs. Further study to explore the mechanism of CA II tumor inhibitory effects will be conducted in our research group.

In this study, CA II was identified by proteomic analysis as a potential biomarker for diagnosis of CRC followed by further verification by molecular biology methods. Moreover, it was shown that CA II might play a role as tumor suppressor gene in cancer development and progression. In conclusion, our data may contribute to a better understanding of the molecular mechanism of CRC and provide insight into colorectal cancer treatment.

Acknowledgements

This study was supported by grants from Chinese NSFC (31171370) and the National 973 Basic Research Program of China (2011CB910703).

References

1. 

Jemal A, Siegel R, Ward E, Hao Y, Xu J, Murray T and Thun MJ: Cancer statistics. CA Cancer J Clin. 58:71–96. 2008.

2. 

Woolf SH: The best screening test for colorectal cancer - a personal choice. N Engl J Med. 343:1641–1643. 2000.

3. 

Walsh JM and Terdiman JP: Colorectal cancer screening: scientific review. JAMA. 289:1288–1296. 2003.

4. 

Jemal A, Murray T, Ward E, et al: Cancer statistics, 2005. CA Cancer J Clin. 55:10–30. 2005.

5. 

Phizicky E, Bastiaens PI, Zhu H, Snyder M and Fields S: Protein analysis on a proteomic scale. Nature. 422:208–215. 2003.

6. 

Alessandro R, Belluco C and Kohn EC: Proteomic approaches in colon cancer: promising tools for new cancer markers and drug target discovery. Clin Colorectal Cancer. 4:396–402. 2005.

7. 

Nedelkov D, Kiernan UA, Niederkofler EE, Tubbs KA and Nelson RW: Population proteomics: the concept, attributes and potential for cancer biomarker research. Mol Cell Proteomics. 5:1811–1818. 2006.

8. 

Tyers M and Mann M: From genomics to proteomics. Nature. 422:193–197. 2003.

9. 

Tong A, Zhang H, Li Z, et al: Proteomic analysis of liver cancer cells treated with suberonylanilide hydroxamic acid. Cancer Chemother Pharmacol. 61:791–802. 2008.

10. 

Dahan L, Sadok A, Formento JL, Seitz JF and Kovacic H: Modulation of cellular redox state underlies antagonism between oxaliplatin and cetuximab in human colorectal cancer cell lines. Br J Pharmacol. 158:610–620. 2009.

11. 

Gilmour KM: Perspectives on carbonic anhydrase. Comp Biochem Physiol A Mol Integr Physiol. 157:193–197. 2010.

12. 

Yoshiura K, Nakaoka T, Nishishita T, et al: Carbonic anhydrase II. A novel biomarker for gastrointestinal stromal tumors. Mod Pathol. 23:743–750. 2010.

13. 

Yoshiura K, Nakaoka T, Nishishita T, et al: Carbonic anhydrase II is a tumor vessel endothelium-associated antigen targeted by dendritic cell therapy. Clin Cancer Res. 11:8201–8207. 2005.

14. 

Haapasalo J, Nordfors K, Järvelä S, et al: Carbonic anhydrase II in the endothelium of glial tumors: a potential target for therapy. Neurooncology. 9:308–313. 2007.

15. 

Korhonen K, Parkkila AK, Helen P, et al: Carbonic anhydrases in meningiomas: association of endothelial carbonic anhydrase II with aggressive tumor features. J Neurosurg. 111:472–477. 2009.

16. 

Kivela AJ, Saarnio J, Karttunen TJ, et al: Differential expression of cytoplasmic carbonic anhydrases, CA I and II and membrane-associated isozymes, CA IX and XII, in normal mucosa of large intestine and in colorectal tumors. Dig Dis Sci. 46:2179–2186. 2001.

17. 

Kummola L, Hämäläinen JM, Kivelä J, Kivelä AJ, Saarnio J, Karttunen T and Parkkila S: Expression of a novel carbonic anhydrase, CA XIII, in normal and neoplastic colorectal mucosa. BMC Cancer. 5:412005.

18. 

Niemelä AM, Hynninen P, Mecklin JP, et al: Carbonic anhydrase IX is highly expressed in hereditary nonpolyposis colorectal cancer. Cancer Epidemiol Biomarkers Prev. 16:1760–1766. 2007.

19. 

Parks SK, Chiche J and Pouyssegur J: pH control mechanisms of tumor survival and growth. J Cell Physiol. 226:299–308. 2011.

20. 

Swietach P, Vaughan-Jones RD and Harris AL: Regulation of tumor pH and the role of carbonic anhydrase 9. Cancer Metastasis Rev. 26:299–310. 2007.

21. 

Pastorekova S, Ratcliffe PJ and Pastorek J: Molecular mechanisms of carbonic anhydrase IX-mediated pH regulation under hypoxia. BJU Int. 101:8–15. 2008.

22. 

Lv L, Li D, Zhao D, et al: Acetylation targets the M2 isoform of pyruvate kinase for degradation through chaperone-mediated autophagy and promotes tumor growth. Mol Cell. 42:719–730. 2011.

23. 

Harris I, McCracken S and Mak TW: PKM2: a gatekeeper between growth and survival. Cell Res. 22:447–449. 2012.

24. 

Kalluri R and Weinberg RA: The basics of epithelial-mesenchymal transition. J Clin Invest. 119:1420–1428. 2009.

25. 

Thiery JP, Acloque H, Huang RY and Nieto MA: Epithelialmesenchymal transitions in development and disease. Cell. 139:871–890. 2009.

26. 

Mallory JC, Crudden G, Oliva A, Saunders C, Stromberg A and Craven RJ: A novel group of genes regulates susceptibility to antineoplastic drugs in highly tumorigenic breast cancer cells. Mol Pharmacol. 68:1747–1756. 2005.

Journal Cover

August 2013
Volume 43 Issue 2

Print ISSN: 1019-6439
Online ISSN:1791-2423

2013 Impact Factor: 2.773
Ranked #30/202 Oncology
(total number of cites)

Sign up for eToc alerts

Recommend to Library

Copy and paste a formatted citation