Peroxisome proliferator-activated receptor γ (PPARγ) is a member of the nuclear hormone receptor family. In colon, this transcription factor is involved in differentiation of absorptive cells. PPARγ participates also in colon carcinogenesis and cancer progression. Two isoforms, namely PPARγ1 and PPARγ2, have been described. Recently, new PPARγ1 transcripts whose translation raises PPARγ1 protein have been characterised. They differ from each other by combination of untranslated exons localised in the 5' UTR of the PPARG gene. Here, we studied whether such a diversity of PPARγ transcripts occurs in human colon cell models. Based on bioinformatic analysis, putative untranslated exons were identified in the human PPARG gene. By RT-PCR analysis, we have demonstrated that several of these untranslated exons are included in PPARγ transcripts from colon-derived cell lines or in those derived from other tissue. Using HT-29 cells, changes in PPARγ1 mRNA levels were observed after treatment with PPARγ agonists such as pioglitazone and troglitazone. These modifications correlated with particular PPARγ transcripts excluding the untranslated exon A2. HT-29 cells treatment with actinomycin D or cycloheximide showed that the presence of PPARγ mRNA including exon A2 was dependent on de novo protein synthesis. We concluded that diverse PPARγ1 mRNA exist in colorectal cells. Levels of PPARγ1 transcript varied according to the phenotype of colon cell model used. We suggest that regulation of PPARγ1 mRNA levels could be dependent in part on the composition of untranslated exon(s) in the 5' UTR of PPARγ1 mRNA.

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