Progesterone Receptors Upregulate Wnt-1 To Induce Epidermal Growth Factor Receptor Transactivation and c-Src-Dependent Sustained Activation of Erk1/2 Mitogen-Activated Protein Kinase in Breast Cancer Cells

Abstract

Progesterone receptor (PR) ligand binding induces rapid and transient (5- to 10-min) activation of cytosolic c-Src-Ras-Erk1/2 mitogen-activated protein kinase (MAPK) signaling that is independent of PR functioning as transcription factors. Here, we have explored the integration of PR-dependent transcription and rapid signaling events in breast cancer cells. PR-B, but not PR-A, induced robust and sustained (6- to 72-h) Erk1/2 activation that was required for elevated cyclin D1 protein but not mRNA levels. Sustained Erk1/2 activation in response to progestins occurred via a novel mechanism distinct from rapid signaling initiated by PR/c-Src interactions and required the PR-B DNA-binding domain (DBD). PR/progestin upregulated epidermal growth factor receptor (EGFR) and Wnt-1. In response to PR-induced Wnt-1 signaling, matrix metalloprotease (MMP)-mediated membrane-proximal shedding of EGFR ligands transactivated EGFR and induced persistent downstream c-Src and Erk1/2 activities. T47D cell anchorage-independent growth was stimulated by progestins and blocked by inhibition of Erk1/2, c-Src, EGFR, or RNA interference of Wnt-1. Similarly, cell growth in soft agar required the PR DBD but was sensitive to disruption of PR/c-Src interactions, suggesting that both PR-B-induced rapid signaling events and nuclear actions contribute to this response. Our discovery that progestins are capable of robust autocrine activation of EGFR and sustained Erk1/2 signaling provides further support for the physiological linkage of growth factor and steroid hormone signaling. PR-B-induced sustained MAPK signaling may provide prosurvival or proliferative advantages to early breast cancer lesions.

We thank Kate Horwitz (University of Colorado Health Sciences Center, Aurora, CO) for the kind gift of the PR-null T47D cell line and T47D variants stably expressing either PR-B or PR-A (57). We acknowledge the assistance of the Flow Cytometry Core Facility of the University of Minnesota Cancer Center, a comprehensive cancer center designated by the National Cancer Institute, supported in part by P30 CA77598.

This work was supported by NIH grant R01 CA123763 (formerly DK053825) to C.A.L. and Department of Defense Predoctoral Fellowship Grant number DAMD17-03-1-0390 to E.J.F.