Recent evidence suggests possible roles of progesterone receptor (PR) in non-small cell lung cancer (NSCLC). However, very little is known about functional roles of PR in NSCLC. PR contains a polyproline domain (PPD), which directly binds to the SH3 domain of signaling molecules. Since PPD-SH3 Interactions are essential for EGF signaling, we hypothesized that the presence of PR-PPD interfered with EGFRmediated signaling and cell proliferation. We examined the role of PR-PPD in cell proliferation and signaling by stably expressing PR-B or PR-B with disrupting mutations in the PPD (PRB~SH3) from a tetracycline-regulated promoter in A549 NSCLC cells. PR-B dose-dependently inhibited cell growth in the absence of ligand, and progestin (R5020) treatment further suppressed cell proliferation. Treatment with RU486 abolished PR-B and R5020 inhibition of cell proliferation. Expression of PR-B~SH3 and treatment with R5020 or RU486 had no effect on cell proliferation. In addition, PR-B but not PR-B~SH3 reduced EGF-induced A549 cell proliferation and EGFinduced activation of MAPK, in the absence of ligand. Together, our data demonstrate the significance of PR extranuclear signaling through PPD Interactions in EGF-mediated proliferation and signaling in NSCLC cells.
