Dephosphorylation of CREB Regulates Its Functions on Lens Differentiation

Abstract

Purpose: Our previous studies have shown that serine/threonine phosphatases-1 and -2A are major lens phosphatases. Inhibition or knockdown of PP-1 and PP-2A activities led to microphthalmia in goldfish and zebrafish. However, the exact mechanisms by which PP-1 and PP-2A regulate lens differentiation remains to be investigated. In the present study, we present evidence to show that PP-1 and PP-2A directly dephosphorylate CREB to regulate lens differentiation.

Methods: Human embryonic lens epithelial cells (FHL-124), mouse lens epithelial cells, wild type and CREB knockout mice were used as testing systems. Co-immunoprecipitation assays were used to investigate the interactions between CREB and PP-1/-2A. Treatment with various kinase inhibitors, and overexpression and knockdown of PP-1 or -2A were used to examine their effects on CREB phosphorylation status. QRT-PCR, Western-blot analysis and reporter gene activity assays were used to study the roles of CREB under various conditions of phosphorylation/dephosphorylation.

Results: Various kinases including PKA, PKC and ERK are implicated in phosphorylating CREB in the ocular lens. Both PP-1 and PP-2A are found capable of dephosphorylating CREB to modulate its transcription activity.

Conclusions: PP-1 and -2A dephosphorylate CREB to modulate its function in lens differentiation. (Supported by EY018380, CSC and HNU)

Keywords: 739 transcription factors • 646 phosphorylation • 497 development