Abstract 3300: Estrogen stimulates cell cycle progression dependent on Src kinase activity and IMP1 stabilization of myc mRNA in estrogen receptor-positive breast cancer cells

Abstract

Abstract Estrogen (E2) stimulation promotes proliferation in estrogen receptor-positive (ER+) breast cancer, which accounts for 60-75% of all breast cancer. E2 signals through the ER via three pathways: the classical genomic pathway involving transcriptional activation of the ER, crosstalk between ER and other transcription factors, and “non-genomic” signaling cascades, which do not involve the transcriptional activity of the ER. This “non-genomic” pathway likely involves Src family kinases (SFKs) and has been implicated in cell cycle progression in fibroblasts engineered to express the ER (Castoria 1999). While not typically amplified or mutationally activated in ER+ breast cancer, Src is hyperactive in most breast cancers. To test whether SFK activity is required for G1/S cell cycle progression in breast cancer cells, we pretreated quiescent ER+ MCF7 cells with a selective SFK inhibitor (SU11333) prior to stimulation with E2. Inhibition of SFK activity blocked progression from G1 to S phase. Previous data from our laboratory has demonstrated that G1/S progression in response to peptide growth factor stimulation of quiescent fibroblasts is dependent upon SFK-mediated stabilization of myc mRNA (Bromann 2005). We therefore tested whether SFK activity also regulates myc expression in breast cancer cells. Our data suggest that SFK activity is required for accumulation of myc mRNA in quiescent MCF7s after E2 stimulation, and that E2 stimulated stabilization of myc mRNA is dependent on SFK activity. One potential myc mRNA stabilizer is IMP1 (IGF2BP1, ZBP1, CRDBP) an RNA binding protein that is primarily expressed during development and in stem cells, and re-expressed in some cancer types, including breast cancer. IMP1 has previously been shown to stabilize myc mRNA in stem cells as well as osteosarcoma cells. While the signaling pathways that mediate this stabilization have not been well studied, previous work has identified a Src phosphorylation site on IMP1 which regulates IMP1 function (Sasaki 2010). We hypothesized that IMP1 may play a role in E2-mediated stabilization of myc mRNA. Indeed, MCF7 cells require IMP1 to accumulate myc mRNA after E2 stimulation. In summary, E2 stimulation activates SFKs, which then promote G1/S cell cycle progression in part by stabilizing myc mRNA levels, through the activity of IMP1. Bromann et al JBC, 2005 Castoria et al. EMBO J, 1999 Sasaki et al. J Neurosci, 2010 Citation Format: Christopher Abdullah, Hasan Korkaya, Sara A. Courtneidge. Estrogen stimulates cell cycle progression dependent on Src kinase activity and IMP1 stabilization of myc mRNA in estrogen receptor-positive breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3300. doi:10.1158/1538-7445.AM2014-3300