Profilin-1 modulates proliferation and survival of breast cancer cells

2600 Objective: Profilin-1 (Pfn1) expression is down-regulated in several different types of adenocarcinoma (breast, pancreas, hepatic) and over-expression of Pfn1 completely suppresses tumorigenicity of breast cancer cell lines in xenograft-based animal models therefore implying that Pfn1 is a tumor-suppressor protein. The objective of the present work is to elucidate the cellular and molecular basis underlying Pfn1’s tumor-suppressive action. Methods: MDA-MB-231 breast cancer cell lines stably expressing either GFP (control) or GFP-Pfn1 were used in the present study. Results: Consistent with their failure to induce tumor formation in xenograft models, GFP-Pfn1 expressing cells displayed dramatically reduced proliferation and increased susceptibility to TNF-induced apoptosis when compared to either parental or GFP-expressers. Immunoblot analyses of cell-cycle markers demonstrated a significant up-regulation in the level of p27kip1, a major cyclin-dependent kinase inhibitor, in Pfn1 over-expressing cells. Furthermore, Pfn1 over-expression decreases the activation of AKT (a PIP3-dependent process that is central to the regulation of cell proliferation and survival) in MDA-MB-231 cells. Consistent with this biochemical finding, we found that Pfn1 over-expressing cells displayed a nearly 2-fold reduction in the fluorescence intensity of PIP3 immunostaining compared to control cells thus suggesting for the first time that perturbing Pfn1 can modulate phosphoinositide-dependent signaling in breast cancer cells. Conclusion: Overall, these results indicate that tumor-suppressive action of Pfn1 for breast cancer cells could be linked to its modulation of both cell proliferation and survival pathways.