FOXO1 regulates oncogenic PKC-ι expression in melanoma inversely to c-Jun in an autocrine manner via IL-17E and ICAM-1 activation
- Wishrawana S. Ratnayke
- Christopher A. Apostolatos
- Sloan Breedy
- Andre H. Apostolatos
- Mildred Acevedo-Duncan
Published online on: October 25, 2018
Copyright: © Ratnayke et al.
This is an open access article distributed under the terms of Creative Commons Attribution License.
Regardless of abundant efforts to enhance primary
prevention and early detection, the number of melanoma cases
in the United States has increased steadily over the past 15
years, thus greatly affecting public health and the economy. In
previous studies, we demonstrated protein kinase C‑ι (PKC‑ι)
to be an oncogene in melanoma, which promotes the activation
of nuclear factor (NF)‑κB, thereby supporting survival and
progression. In addition, we demonstrated that PKC‑ι induced
the metastasis of melanoma cells by activating Vimentin, and
PKC‑ι inhibition downregulated epithilial‑mesencymal transi‑
tion (EMT), while inducing apoptosis. Of note, PKC‑ι specific
inhibitors downregulated the expression of both PKC‑ι and
phosphorylated PKC‑ι, suggesting that PKC‑ι plays a role
in regulating its own expression in melanoma. In this study,
we report the underlaying mechanisms of the transcriptional
regulation of PKC‑ι (PRKCI gene) expression in melanoma.
c‑Jun, interferon‑stimulated gene factor 3 (ISGF3), paired box
gene 3 (PAX3), early growth response protein 1 (EGR1) and
Forkhead box protein O1 (FOXO1), which bind on or near the
promoter sequence of the PRKCI gene, were analyzed for their
role in PKC‑ι regulation in SK‑MEL‑2 and MeWo cell lines.
We silenced selected transcription factors using siRNA, and
the results revealed that the silencing of c‑Jun and FOXO1
significantly altered the expression of PRKCI. The levels of
both phosphorylated and total PKC‑ι increased upon FOXO1
silencing and decreased upon c‑Jun silencing, suggesting that
c‑Jun acts as an upregulator, while FOXO1 acts as a down‑
regulator of PRKCI expression. We also used a multiplex
ELISA to analyze multiple pathways other than NF‑κB that
were affected by treatment with PKC‑ι inhibitor. The silencing
of NF‑κB p65 and PKC‑ι by siRNA suggested that the regula‑
tion of PKC‑ι expression was strongly associated with FOXO1.
In addition, we observed a significant decrease in the mRNA
levels of both interleukin (IL)‑6 and IL‑8, with a significant
increase in the levels of IL‑17E and intercellular adhesion
molecule 1 (ICAM‑1) upon the knockdown of expression of
PKC‑ι in both cell lines. This suggested that PKC‑ι expres‑
sion was affected by these cytokines in an autocrine manner.
Overall, the findings of this study suggest that PKC‑ι inhibi‑
tion suppresses its own expression, diminishing oncogenic
signaling, while upregulating anti‑tumor signaling, thus
rendering it an effective novel biomarker for use in the design
of novel targeted therapeutics for melanoma.