Requirement of protein L-isoaspartyl O-methyltransferase for transcriptional activation of trefoil factor 1 (TFF1) gene by estrogen receptor alpha

Lysine- and arginine-specific methyltransferases have been shown to act as either direct or secondary transcriptional co-activator of the estrogen receptor (ER alpha). However, little is known about the role of protein t-isoaspartyl O-methyltransferase (PIMT) on transcriptional regulation. Here, we show that PIMT acts as a co-activator for ER alpha-mediated transcription. Activation of the estrogen response element (ERE) promoter by beta-estradiol (E-2) was suppressed by knockdown of PIMT, and enhanced by overexpression of wild-type PIMT. However, the ERE promoter activity was resistant to E-2 stimulation in cells overexpressing a catalytically inactive PIMT mutant, G88A. Consistent with these results, the expression of the endogenous ER alpha response gene trefoil factor 1 (TFF1) by E-2 was completely abrogated by PIMT depletion and decreased to approximately 50% when PIMT mutant G88A was expressed. In addition, over-expression of PIMT significantly increased the levels of TFF1 mRNA in the presence or absence of E2. Interestingly, PIMT interacted with ER alpha and was distributed to the cytosol and the nucleus. The chromatin immunoprecipitation analysis revealed that PIMT was recruited to the promoter of TFF1 gene together with ER alpha in an E-2-dependent manner, which was accompanied by uploading of RNA polymerase II on the promoter. Taken together, the results suggest that PIMT may act as a co-activator in ER alpha-mediated transcription through its recruitment to the promoter via interacting with ER alpha. (C) 2012 Elsevier Inc. All rights reserved.