Transcriptional repression of the tyrosinase-related protein 2 gene by transforming growth factor-β and the Kruppel-like transcription factor GLI2.
BACKGROUND
Tyrosinase-Related Protein 2 (TRP2) is an enzyme involved in melanogenesis, that also exerts proliferative, anti-apoptotic and immunogenic functions in melanoma cells. TRP2 transcription is regulated by the melanocytic master transcription factor MITF. GLI2, a transcription factor that acts downstream of Hedgehog signaling, is also a direct transcriptional target of the TGF-β/SMAD pathway that contributes to melanoma progression and exerts transcriptional antagonistic activities against MITF.


OBJECTIVES
To characterize the molecular events responsible for TGF-β and GLI2 repression of TRP2 expression.


METHODS
In silico promoter analysis, transient cell transfection experiments with 5'-end TRP2 promoter deletion constructs, chromatin immuno-precipitation, and site-directed promoter mutagenesis were used to dissect the molecular mechanisms of TRP2 gene regulation by TGF-β and GLI2.


RESULTS
We demonstrate that TGF-β and GLI2-specific TRP2 repression involves direct mechanisms that occur in addition to MITF downregulation by TGF-β and GLI2. We identify two functional GLI2 binding sites within the TRP2 promoter that are critical for TGF-β and GLI2 responsiveness, one of them overlapping a CREB binding site. GLI2 and CREB competing for the same cis-element is associated with opposite transcriptional outcome.


CONCLUSION
Our results further refine the understanding of how TGF-β and GLI2 control the phenotypic plasticity of melanoma cells. In particular, we identify critical GLI2-binding cis-elements within the TRP2 promoter region that allow for its transcriptional repression independently from MITF concomitant downregulation.
['Pierrat|Marie-Jeanne|MJ|', 'Marsaud|Véronique|V|', 'Mauviel|Alain|A|', 'Javelaud|Delphine|D|']
D045744:Cell Line, Tumor D019295:Computational Biology D015972:Gene Expression Regulation, Neoplastic D006801:Humans D019746:Intramolecular Oxidoreductases D008545:Melanoma D016297:Mutagenesis, Site-Directed D009687:Nuclear Proteins D011401:Promoter Regions, Genetic D012878:Skin Neoplasms D014158:Transcription, Genetic D016212:Transforming Growth Factor beta D000075746:Zinc Finger Protein Gli2
Kruppel-like transcription factor GLI2 Melanoma TGF-β CREB Microphtalmia transcription factor Transcriptional control Tyrosine-related protein 2