Abstract P2-05-01: Induction of PELP1 expression in mammary gland promotes tumorigenesis by enhancing CDK-CyclinD1 signaling

Abstract

Introduction: Estrogen receptor coregulator over-expression promotes carcinogenesis and/or progression of endocrine related-cancers where steroid hormones are powerful mitogenic agents. Recent studies in our laboratory as well as others demonstrated that PELP1 is a proto-oncogene and a prognostic indicator of decreased survival in breast cancer patients. Recent studies indicated that PELP1 is needed for optimal epigenetic modifications at ER target genes and PELP1 interactions with KDM1 play a key role in PELP1 mediated oncogenic functions. However, the in vivo significance of PELP1 deregulation during initiation and progression of breast cancer remains unknown. The objective of this study is determine the molecular mechanisms by which PELP1 regulate breast cancer progression in vivo. Method: To determine the significance of PELP1 over-expression in mammary tumorigenesis, we used an inducible, tissue-specific PELP1 expressing transgenic mouse. Mammary epithelial-specific expression of PELP1 was validated by immunohistochemistry and Western blot analysis. PELP1-mediated morphological and histological changes were analyzed by examining carmine-stained whole mounts and H&E-stained paraffin embedded mammary glands sections. Differential expression of breast cancer-focused genes between wild type and PELP1 transgenic mammary glands was determined using real-time RT2 Profiler PCR array. Proliferation was analyzed using Ki-67 immuno staining. RTqPCR, Western and IHC analysis were used to confirm the changes in the expression of PELP1 regulated genes. Results: We observed an increase in proliferation, extensive side branching and precocious differentiation in PELP1 expressing mammary gland compared to controls. Aged MMTVrtTA-TetOPELP1 bitransgenic mice revealed hyperplasia and preneoplastic changes as early as 12 weeks and mammary tumors occurred at a latency of 10.5 months. Mechanistic studies using tissues from control and PELP1 transgenic mice revealed that PELP1 deregulation modulates expression of a number of known ER target genes involved in cellular proliferation (such as cyclin D1, CDKs) and morphogenesis (EGFR, MMPs) and such changes facilitated altered mammary gland morphogenesis and tumor progression. Western and IHC analysis of mammary glands confirmed upregulation of CDK and Cyclin D1 protein levels in PELP1 Tg mice. Further, PELP1 is hyperphosphorylated at CDK phosphorylation site in PELP1 (Ser 991), suggesting an autocrine loop involving CDk-CyclinD1-PELP1 axis in promoting mammary tumorigenesis. Treatment of PELP1 Tg mice with pargyline, an inhibitor of KDM1 for four months significantly reduced PELP1 driven hyperplasia. Mechanistic studies revealed that pargyline treatment reduced cyclin D1 expression levels and substantially reduced CDK driven PELP1 phosphorylation. Conclusions: PELP1 deregulation modulates expression of a number of known ER target genes and cancer promoting genes. PELP1 mediated epigenetic changes via KDM1 play role in PELP1 oncogenic functions in vivo. Collectively, these results support that PELP1 deregulation has potential to promote breast tumorigenesis in vivo. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-05-01.