Abstract 4607: Novel role of PARP4 in hormone-dependent breast cancer progression and metastasis
Authors: Nair Hareesh Babu Bhaskaran , Krishnegowda Naveen , Nair Binoj , Ganapathy Manonmani , S Olga , Kirma Nameer , Vadlamudi Ratna , Tekmal Rajeshwar 
Published: February 2011

Abstract
Estrogen/estrogen receptor-mediated actions play an important role in regulating a variety of biological process including development, homeostasis and breast cancer progression. Even though systemic hormone therapies that either block local estrogen production by aromatase inhibitors (AI) or block actions of estrogen/estrogen receptor (ER) by antiestrogens (AE) is well tolerated, the development of resistance to these agents is still a major concern. Since multiple signaling pathways involved in ER activation, combination of endocrine and non endocrine agents that block these signaling pathways may delay the onset of resistance to hormonal therapy. Recent studies from our laboratory have identified Poly(ADP-ribose) polymerase 4(PARP4) as a novel ER co-regulator. We have investigated with hormone resistant breast cancer cells to demonstrate whether blocking of PARP4 results in resensitization to hormone therapies. PARP comprise of a family of enzymes which catalyses poly(ADPribosyl) action of DNA-binding proteins. PARP-1, the best characterized member, however PARP4 is an understudied protein with numerous capabilities. PARP4 has both N-terminal PXXP and PPXXP motifs which are known to interact with SH3 domain of c-Src as well as LXXLL motif which interacts with estrogen receptor (ER). We show that PARP4 is widely expressed in breast cancer cells (MCF-7, MDA-MB-231, ZR-75, and SKBR3) and its expression is significantly higher in these cells compared to non malignant MCF-10A cells. To understand the important role of PARP4-ER axis in hormonal resistance, metastasis and to test whether blocking of PARP4 mediated actions provide a therapeutic advantage to treat endocrine resistant breast tumors, we have used hormone resistant breast cancer cells that over-express PARP4 or and treated with PARP4 siRNA nanoparticles. The PLGA-siRNA nanoparticles were designed multifunctionally using chemical conjugation. The nanoparticles were characterized physiochemically. Our studies show that PARP4 functionally interacts with ER. As demonstrated by immunoprecipitation, PARP4 interacts with ER upon ligand (E2)-mediated stimulation. PARP4 induces cell cycle progression, local aromatase activity and promotes in vitro tumorigenic potential of breast cancer cells. siRNA nanoparticles of PARP4 inhibit the metastatic incidence in vivo. Our study also shows that PARP4-ER axis enhances multiple signaling cross-talk leading to hormonal independence/resistance and metastasis. Our results suggests that targeting PARP4 may provide a therapeutic advantage to treat endocrine resistant tumors and blocking the development of resistance to hormonal therapeutic agents and as well as decrease the metastatic potential in therapy resistant breast tumors. (Supported by NIH/NCI P30 CA 54174, RRT)
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4607.