Palladin expression contributes to invasive motiliy in metastatic breast cancer cells.

Abstract

Abstract Abstract #6018 Background: Cancer metastasis involves multiple actin-dependent steps, including intravasation , extravasation, and adhesion. Therefore, it is important to understand the molecular mechanisms that control cytoskeletal dynamics in metastatic cells. Palladin is an actin-binding protein that functions as a key molecular scaffold involved in actin organization. Recent studies showed that (1) a mutation in palladin is linked to a rare form of familial pancreatic cancer, (2) palladin is overexpressed in many sporadic pancreatic tumors, and (3) palladin is upregulated in pancreatic tumor-associated fibroblasts. However, palladin's functions in other invasive cancers have not been well elucidated.
 Methods: Three primary human breast cancer specimens, three metastatic breast cancer specimens and three samples of benign breast tissue were obtained from the UNC Tissue Procurement Facility. Extracts were analyzed using western blots. Eight human breast cancer cell lines, which differ in their metastatic potential, were used: T47D, BT474, ZR75.1 and MCF-7, BT549, Hs578T, MDA-MB-231 and SUM159. Western blots were performed to determine the level of palladin in all cells lines. siRNA and virus infection approaches were used to reduce and overexpress palladin levels, respectively. Cell migration was analyzed in transwell inserts. Invasion experiments were conducted in Matrigel invasion chambers. Podosome formation was induced with the phorbol ester PDBu.
 Results: Immunoblot analysis revealed that palladin levels are higher overall in primary tumors and metastases, when compared to benign breast tissue. Immunohistochemistry showed that palladin staining is associated with ductal epithelial cells and tumor cells. In breast cancer cells, palladin expression closely correlates with metastatic potential: palladin levels were ∼16 fold higher in invasive cells than in non-invasive cells. Furthermore, knockdown of palladin resulted in a significant reduction in the ability of SUM159 cells to migrate through a transwell filter, and to invade through a layer of Matrigel. Phorbol ester treatment stimulated the formation of palladin-containing podosomes in SUM159 and MDA-MB-231, but not MCF7 cells. Palladin knockdown also impaired the ability of SUM159 cells to assemble podosomes. Palladin overexpression promotes podosome formation but does not affect cell migration.
 Discussion: Our results show that palladin plays an important role in podosome formation, and thus high levels of palladin expression may contribute to the invasive motility of metastatic breast cancer cells by facilitating the assembly of these structures. Our results also show that overexpression of palladin alone is not sufficient to trigger enhanced invasive motility in cultured human breast cancer cells. These results support a model in which a cohort of genes are coordinately upregulated in metastatic cells, contributing to specific aspects of invasive cell motility. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6018.