Insulin-like growth factor-I regulates GPER expression and function in cancer cells

Functional cross talk between insulin-like growth factor-I (IGF-I) system and estrogen signaling has been largely reported, although the underlying molecular mechanisms remain to be fully elucidated. As GPR30/GPER mediates rapid cell responses to estrogens, we evaluated the potential of IGF-I to regulate GPER expression and function in estrogen receptor (ER)α-positive breast (MCF-7) and endometrial (Ishikawa) cancer cells. We found that IGF-I transactivates the GPER promoter sequence and upregulates GPER mRNA and protein levels in both cells types. Similar data were found, at least in part, in carcinoma-associated fibroblasts. The upregulation of GPER expression by IGF-I involved the IGF-IR/PKCδ/ERK/c-fos/AP1 transduction pathway and required ERα, as ascertained by specific pharmacological inhibitors and gene-silencing. In both MCF-7 and Ishikawa cancer cells, the IGF-I-dependent cell migration required GPER and its main target gene CTGF, whereas the IGF-I-induced proliferation required both GPER and cyclin D1. Our data demonstrate that the IGF-I system regulates GPER expression and function, triggering the activation of a signaling network that leads to the migration and proliferation of cancer cells.