Abstract 102: IGFBP6 modulates estrogen receptor alpha phosphorylation and transcriptional activity in breast cancer cells

Abstract

Abstract Insulin-like growth factors (IGFs) are signaling proteins which bind to insulin-like growth factor 1 receptor (IGF-1R) and induce a signaling cascade to promote proliferation and survival in breast cancer cells. Insulin-Like Growth Factor Binding Protein 6 (IGFBP-6) induces apoptosis by inhibiting IGF-1R upon binding to both IGF-1 and IGF-2, however, the role of IGFBP-6 in breast cancer has not been adequately studied. While IGFBP-6 can bind to both IGF-1 and IGF-2, the binding affinity for IGF2 is 20-fold higher compared to IGF1. To determine if IGFBP-6 modulates breast cancer cells, MCF-7 and T-47D cells were stably transfected with an IGFBP-6 expression plasmid. IGFBP6 over-expression resulted in decreased proliferation rates in both cell lines when compared to empty vector controls. To identify a mechanism of decreased proliferation rates, the activation of the IGF-1R-dependent AKT and MAPK mediators was measured. Reduced phosphorylation of MAPK and AKT was observed in both cell lines over-expressing IGFBP-6 compared to empty vector controls. MAPK and AKT phosphorylate ERα at serine 118 and serine 167 respectively, therefore, ERα phosphorylation at these residues was determined in the presence of IGFBP6 expression. Reduction in phosphorylation was greater in MCF-7 cells than T-47D cells when IGFBP6 was constitutively expressed. To determine if reduced ERα phosphorylation altered expression of known targets of ERα-modulated expression, such as IGF-1R and Progesterone Receptor (PR) was measured. Unexpectedly, IGF-1R and PR protein and transcript levels were greater in IGFBP6 over-expressing cells. Studies have shown that differences in ERα phosphorylation change the recruitment of transcriptional modulators associated with ERα-mediated transcription. These results suggest that despite reducing IGF-1R-dependent cell signaling, compensatory mechanisms may be induced to enhance ERα-mediated expression. Citation Format: Francisco Javier Lariz, Kevin D. Houston. IGFBP6 modulates estrogen receptor alpha phosphorylation and transcriptional activity in breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 102.