title: Heregulin-triggered Her-2/neu signaling enhances nuclear accumulation of p21WAF1/CIP1 and protects breast cancer cells from cisplatin-induced genotoxic damage.
abstract: Elevated levels of p21WAF1/CIP1, an important mediator of DNA repair, have been observed in various aggressive tumors as well as linked to chemoresistance. We examined whether heregulin (HRG), a member of the EGF-like growth factor family closely related to breast cancer tumorigenesis and metastasis, modulates p21WAF1/CIP1 expression and cellular localization. We used a model system that consisted of MCF-7 cells and MCF-7 cells engineered to overexpress the full-length cDNA of the human HRG gene (MCF-7/HRG). MCF-7/HRG cells demonstrate constitutive hyperactivation of Her-2/neu receptor as well as activation of down-stream PI-3'K/AKT and MAPK signaling cascades. Immunoblotting analyses showed that MCF-7/HRG cells significantly up-regulate p21WAF1/CIP1 expression relative to control MCF-7/pBABE cells, while a strong nuclear accumulation of p21WAF1/CIP1 in MCF-7/HRG cells was revealed by immunofluorescence microscopy studies. Protein degradation analyses demonstrated that the half-life of p21WAF1/CIP1 protein was increased from approximately 35 min in control MCF-7/pBABE cells to >/=3 h in MCF-7/HRG cells. Pharmacological inactivation of the PI-3'K/AKT and MAPK completely prevented HRG-induced accumulation of p21WAF1/CIP1. A structural deletion mutant of HRG (HRG-M4) lacking the N-terminus sequence and the cytoplasmic-transmembrane region of HRG was generated to investigate whether secretion of HRG and transactivation of Her-2/neu actively contributed to HRG-regulated p21WAF1/CIP1 expression and cellular localization. MCF-7 cells engineered to overexpress HRG-M4 did not demonstrate either activation of Her-2/neu, PI-3'K/AKT, or MAPK. Remarkably, HRG-M4 overexpression completely abolished the ability of HRG to promote nuclear accumulation of p21WAF1/CIP1 and concomitantly enhanced the apoptotic effects of cisplatin towards breast cancer cells. This novel interplay between HRG and p21WAF1/CIP1 strongly suggests that one mechanism of HRG-regulated breast cancer cell proliferation, survival, and/or sensitivity to genotoxic damage is to stabilize and promote a nuclear accumulation of p21WAF1/CIP1.
authors.affiliation: Department of Medicine, Evanston Northwestern Healthcare Research Institute, Evanston, IL 60201, USA.
authors.forename: Javier A
authors.initials: JA
authors.lastname: Menendez
authors.forename: Inderjit
authors.initials: I
authors.lastname: Mehmi
authors.forename: Ruth
authors.initials: R
authors.lastname: Lupu
mesh_terms: D000970:Antineoplastic Agents / Q000633:toxicity*; D001943:Breast Neoplasms / Q000473:pathology*; D018797:Cell Cycle Proteins / Q000493:pharmacokinetics*; D049109:Cell Proliferation; D002470:Cell Survival; D002945:Cisplatin / Q000633:toxicity*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004249:DNA Damage; D004260:DNA Repair; D019008:Drug Resistance, Neoplasm; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D020890:Neuregulin-1 / Q000235:genetics* / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D002945:Cisplatin; D050759:Cyclin-Dependent Kinase Inhibitor p21; D020890:Neuregulin-1; D018719:Erb-b2 Receptor Tyrosine Kinases; C493956:CDKN1A protein, human