The histidine triad protein Hint1 interacts with Pontin and Reptin and inhibits TCF-beta-catenin-mediated transcription.
Pontin and Reptin previously were identified as nuclear beta-catenin interaction partners that antagonistically modulate beta-catenin transcriptional activity. In this study, Hint1/PKCI, a member of the evolutionary conserved family of histidine triad proteins, was characterised as a new interaction partner of Pontin and Reptin. Pull-down assays and co-immunoprecipitation experiments show that Hint1/PKCI directly binds to Pontin and Reptin. The Hint1/PKCI-binding site was mapped to amino acids 214-295 and 218-289 in Pontin and Reptin, respectively. Conversely, Pontin and Reptin bind to the N-terminus of Hint1/PKCI. Moreover, by its interaction with Pontin and Reptin, Hint1/PKCI is associated with the LEF-1/TCF-beta-catenin transcription complex. In this context, Hint1/PKCI acts as a negative regulator of TCF-beta-catenin transcriptional activity in Wnt-transfected cells and in SW480 colon carcinoma cells as shown in reporter gene assays. Consistent with these observations, Hint1/PKCI represses expression of the endogenous target genes cyclin D1 and axin2 whereas knockdown of Hint1/PKCI by RNA interference increases their expression. Disruption of the Pontin/Reptin complex appears to mediate this modulatory effect of Hint1/PKCI on TCF-beta-catenin-mediated transcription. These data now provide a molecular mechanism to explain the tumor suppressor function of Hint1/PKCI recently suggested from the analysis of Hint1/PKCI knockout mice.
Weiske
Jörg
J
Institute of Clinical Chemistry and Pathobiochemistry, Charité Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
Huber
Otmar
O
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D004265:DNA Helicases / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D051820:TCF Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D051176:beta Catenin / Q000037:antagonists & inhibitors* / Q000378:metabolism
C063306:HINT1 protein, human; D009419:Nerve Tissue Proteins; D051820:TCF Transcription Factors; D015534:Trans-Activators; D014157:Transcription Factors; D051176:beta Catenin; D019938:Cyclin D1; D004265:DNA Helicases