Cyclophilin B as a co-regulator of prolactin-induced gene expression and function in breast cancer cells.
ABSTRACT The effects of prolactin (PRL) during the pathogenesis of breast cancer are mediated in part though Stat5 activity enhanced by its interaction with its transcriptional inducer, the prolyl isomerase cyclophilin B (CypB). We have demonstrated that knockdown of CypB decreases cell growth, proliferation, and migration, and CypB expression is associated with malignant progression of breast cancer. In this study, we examined the effect of CypB knockdown on PRL signaling in breast cancer cells. CypB knockdown with two independent siRNAs was shown to impair PRL-induced reporter expression in breast cancer cell line. cDNA microarray analysis was performed on these cells to assess the effect of CypB reduction, and revealed a significant decrease in PRL-induced endogenous gene expression in two breast cancer cell lines. Parallel functional assays revealed corresponding alterations of both anchorage-independent cell growth and cell motility of breast cancer cells. Our results demonstrate that CypB expression levels significantly modulate PRL-induced function in breast cancer cells ultimately resulting in enhanced levels of PRL-responsive gene expression, cell growth, and migration. Given the increasingly appreciated role of PRL in the pathogenesis of breast cancer, the actions of CypB detailed here are of biological significance.
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ABSTRACT: The role of the polypeptide hormone prolactin (PRL) in the pathogenesis and progression of human breast cancer has become established in recent years. Acting at the autocrine/paracrine level, PRL functions to stimulate the growth and motility of human breast cancer cells. These actions require the presence of the transmembrane prolactin receptor (PRLr). The classic belief is that the PRLr functions "at a distance" through the activation of signaling networks. However, numerous reports now indicate that intact transmembrane receptors localize to the nucleus and directly contribute to transcriptional activation. Yet, without DNA binding capabilities or intrinsic chromatin remodeling activity, the mechanism by which these receptors serve to regulate transcription remains elusive. In this thesis, we investigate the function of nuclear PRLr, given preliminary observations of its nuclear presence. For the first time, we find that the prolactin receptor (PRLr) localizes to the nucleus where it functions as a co-activator through interaction with the latent transcription factor Stat5a and the high mobility group N2 protein (HMGN2). We identify a novel transactivation domain (TAD) within the PRLr and demonstrate that it is activated by ligand-induced phosphorylation, an event coupled to HMGN2 binding. Depletion of HMGN2 reduces binding of PRLr and Stat5a to chromatin, and results in impaired Stat5adrive gene expression. We propose that the PRLr-mediated recruitment of HMGN2 facilitates PRLr/Stat5a assembly onto chromatin, thus enabling Stat5a-driven transcription. These data are of significant importance to the broad field of signal transduction as they expand the growing field of cell surface receptor nuclear localization to include a novel receptor. In addition, these studies are of note as they elucidate a molecular mechanism though which cell surface receptor-mediated transcriptional regulation is achieved.02/2011;