Growth Factor Regulation of Estrogen Receptor Coregulator PELP1 Functions via Protein Kinase A Pathway

Abstract

PELP1 (proline-rich, glutamic acid -rich, and leucine-rich protein-1) is a potential proto-oncogene that functions as a coregulator of estrogen receptor (ER), and its expression is deregulated during breast cancer progression. Emerging evidence suggests growth factor signaling crosstalk with ER as one possible mechanism by which breast tumors acquire resistance to therapy. In this study, we examined mechanisms by which growth factors modulate PELP1 functions, leading to activation of ER. Using in vivo labeling assays, we have found that growth factors promote phosphorylation of PELP1. Utilizing a panel of substrate-specific phosphorylated antibodies, we discovered that growth factor stimulation promotes phosphorylation of PELP1 that is recognized by a protein kinase A (PKA) substrate -specific antibody. Accordingly, growth factor -mediated PELP1 phosphorylation was effectively blocked by PKA-specific inhibitor H89. Utilizing purified PKA enzyme and in vitro kinase assays, we obtained evidence of direct PELP1 phosphorylation by PKA. Using deletion and mutational analysis, we identified PELP1 domains that are phosphorylated by PKA. Interestingly, site-directed mutagenesis of the putative PKA site in PELP1 compromised growth factor -induced activation and subnuclear localization of PELP1 and also affected PELP1-mediated transactivation function. Utilizing MCF-7 cells expressing a PELP1 mutant that cannot be phosphorylated by PKA, we provide mechanistic insights by which growth factor signaling regulates ER transactivation in a PELP1-dependent manner. Collectively, these findings suggest that growth factor signals promote phosphorylation of ER coactivator PELP1 via PKA pathway, and such modification may have functional implications in breast tumors with deregulated growth factor signaling. (Mol Cancer Res 2008;6(5):851 -61)

The prognostic significance of PELP1 expression in invasive breast cancer with emphasis on the ER-positive luminal-like subtype

“…Regulation of aromatase by PELP1 represents a novel mechanism for autocrine oestrogen synthesis, which may lead to tumour proliferation [3]. These findings suggest an important tumourigenic role of PELP1 and may open a new targeted therapeutic approach by its inhibition [4].…”

The Histone Variant MacroH2A1 Regulates Target Gene Expression in Part by Recruiting the Transcriptional Coregulator PELP1

“…In addition, this finding brings up an interesting question of whether or not PELP1 interacts with other macrodomain-containing proteins. Interestingly, both PELP1 and macroH2A1 are subject to a variety of posttranslational modifications (57,62,(74)(75)(76)(77), which may modulate the ability of these factors to interact. Further studies are required to determine the mechanisms that regulate these interactions.…”

The social network of PELP1 and its implications in breast and prostate cancers

“…Several studies have indicated that the deregulation of PELP1 contributes to therapy resistance and that the knockdown of PELP1 or blockage of PELP1-mediated extranuclear signaling sensitizes cells to therapy , Nagpal et al 2008, Kumar et al 2009. Interestingly, the subcellular localization of PELP1 is dysregulated in tumors with a cytosolic predominance in a subset of endometrial tumors, which exhibit resistance to tamoxifen anti-hormonal therapy.…”