Abstract 436: The Fat1 Cadherin Intracellular Domain Interacts with Atrophin Proteins and Recruits Robust Transcription Activity
Background: We recently reported that the atypical cadherin Fat1 is strongly induced after arterial injury, inhibits growth and promotes migration of vascular smooth muscle cells (VSMCs), and can undergo cleavage, with subsequent translocation of its intracellular domain (Fat1IC) to the cell nucleus. In Drosophila, dFat and Atrophin, a nuclear receptor transcriptional corepressor implicated in the control of cell polarity and migration, have been linked by both physical and genetic interaction. Together, these findings suggest an important integrative role for Fat1 in active vascular remodeling, and raise the possibility that some Fat1 effects are mediated from the nucleus via interaction with transcriptional regulators.
Objectives, methods, findings: We hypothesized that the interaction of mammalian Fat1IC with nuclear proteins, such as the mammalian Atrophin homologues atro-1 and atro-2, might contribute to the phenotypic effects of Fat1 on VSMC activation. To test for such interactions, we performed co-immunoprecipitation and Western analysis, identified a physical interaction of Fat1 with atro-1 and atro-2, and mapped necessary Fat1IC sequences to a discrete domain. Immunocytochemical staining showed partial co-localization of Fat1 and atro-1 and -2 in the nucleoplasm. In mammalian two-hybrid assays, surprisingly, tethering of the Fat1IC to DNA yielded very robust transcriptional activation, not repression. This activity was augmented by COUP-TFs, orphan nuclear receptor transcription factors known to associate with atrophins and implicated in both angiogenesis and cardiac development, but not previously linked to Fat1. The biological relevance of these interactions is further supported by quantitative PCR analysis that showed induction of both atro-1 and atro-2 mRNAs after vascular injury, similar to the pattern we identified for Fat1.
Conclusion: The biological significance and molecular functions of the multiple cadherin superfamily proteins expressed in VSMCs are not well understood. Our studies demonstrate the physical and functional interaction of the Fat1IC with multiple nuclear proteins involved in transcriptional regulation, and point to novel pathways by which Fat1 may affect VSMC growth and migration.