PIAS1 Interacts with and Activates PITX2 Transcriptional Activity

Sumoylation plays a key role in orofacial development by facilitating transcriptional regulation. Objectives: PITX2 is a bicoid-like homeodomain transcriptional factor that plays a very important role in tooth development. Protein inhibitors of activated STAT (PIAS) proteins function as SUMO E3 ligases. PIAS-mediated sumoylation of target proteins play important roles in a wide range of cellular processes, including transcriptional control and protein-protein interactions. However, the molecular mechanisms of post-translational modifications of PITX2 are not very well characterized during tooth development. We ask if PIAS1 is a regulator for PITX2 transcriptional activity and interacts with PITX2. Methods: We use transient transfection, GST-pull-down, immunoprecipitation and immunohistochemistry in cell culture and mouse embryonic tissue. Results: PITX2 contains 3 consensus sumoylation sites, but it is not sumoylated. However, PIAS1 physically interacts with PITX2 to regulate its transcriptional activity. PITX2, Lef-1 and â-catenin synergistically activate the LEF-1 2700 promoter in the presence of PIAS1. PITX2 and PIAS1 proteins co-localize in cells. Conclusion: We demonstrate that PIAS1 interacts with PITX2 to activate the transcriptional activity of PITX2 in sumoylation independent manner. This study demonstrates a novel role for PIAS1 in regulating PITX2 transcriptional activity and PIAS1 interaction through a specific domain of PITX2. Support for this research was provided from grant DE13941 from the National Institute of Dental and Craniofacial Research.