Protein Phosphatase-1 Modulates The Function Of Pax-6

Pax-6 is an evolutionarily conserved transcription factorand acts high up in the regulatory hierarchy controlling eyeand brain development in human, mouse, zebrafish, andDrosophila.Previous studies have shown that Pax-6 is aphosphoprotein and its phosphorylation by ERK, p38 andhomeodomain-interacting protein kinase 2 greatly enhances itstransactivation activity. However, the protein phosphatasesresponsible for the dephosphorylation of Pax-6 remain unknown.Here, we present both in vitro and in vivo evidence toshow that protein serine/threonine phosphatase-1 is a majorphosphatase, which directly dephosphorylates Pax-6. First,purified protein phosphatase-1 directly dephosphorylates Pax-6 in vitro. Second, immunoprecipitation-linked Western blotrevealed that both protein phosphatase-1αand proteinphosphatase-1βinteract with Pax-6. Thirdly, overexpressionof protein phosphatase-1αin human lens epithelial cellsleads to dephosphorylation of Pax-6. Finally, inhibition ofprotein phosphatase-1 activity by calyculin A or knockdown ofprotein phosphatase-1αand protein phosphatase-1βby RNAileads to enhanced phosphorylation of Pax-6. Moreover, ourresults also demonstrate that dephosphorylation of Pax-6 byprotein phosphatase-1 significantly modulates its function inregulating expression of both exogenous and endogenous genes.These results demonstrate that PP-1 acts as a major phosphatase to dephosphorylate Pax-6 and modulate itsfunction.