title: Hormonal regulation of the Grb14 signal modulator and its role in cell cycle progression of MCF-7 human breast cancer cells.
abstract: Growth factor receptor bound (Grb)14 is a member of the Grb7 family of src homology (SH)2 domain-containing proteins. These proteins perform both adaptor and modulatory roles in receptor tyrosine kinase (RTK) signaling, although their regulation is poorly understood. In this study, a positive correlation between Grb14 protein expression and ER alpha status in breast cancer cell lines led us to investigate regulation of Grb14 by estradiol and insulin, which synergize in the regulation of breast cancer cell proliferation. In MCF-7 cells maintained in charcoal-stripped serum, Grb14 expression was downregulated by estradiol and increased by the pure anti-estrogen ICI 182780. Under serum-free conditions, insulin enhanced Grb14 expression but this effect was repressed by estradiol when both hormones were used in combination. Using a system in which c-Myc induction drives cell cycle progression independently of estradiol, we demonstrated that Grb14 regulation was specific to estradiol treatment. Finally, we demonstrated a novel functional role for Grb14 whereby its overexpression inhibited not only insulin- but also estrogen-induced cell cycle progression. This was associated with decreased extracellular signal-regulated kinase (Erk)1/2 activation in insulin-stimulated Grb14-overexpressing cells. These data represent the first demonstration of regulation of Grb14 expression levels in response to hormonal stimuli, and are consistent with its role as a repressor of insulin signaling where it is induced as a negative feedback mechanism. A role for Grb14 is also shown in estrogen/insulin crosstalk since estradiol blocks the insulin-induced induction of this protein.
authors.affiliation: Cancer Research Program, Garvan Institute of Medical Research, St Vincent's Hospital, Sydney, New South Wales, Australia.
authors.forename: Rania
authors.initials: R
authors.lastname: Kairouz
authors.forename: Jayamala
authors.initials: J
authors.lastname: Parmar
authors.forename: Ruth J
authors.initials: RJ
authors.lastname: Lyons
authors.forename: Alexander
authors.initials: A
authors.lastname: Swarbrick
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Musgrove
authors.forename: Roger J
authors.initials: RJ
authors.lastname: Daly
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D001943:Breast Neoplasms / Q000378:metabolism* / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D004965:Estrogen Antagonists / Q000494:pharmacology; D025461:Feedback, Physiological / Q000187:drug effects; D005260:Female; D000077267:Fulvestrant; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D004965:Estrogen Antagonists; C099655:GRB14 protein, human; D007004:Hypoglycemic Agents; D007328:Insulin; D011506:Proteins; D000077267:Fulvestrant; D004958:Estradiol; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3