Functional corelation between paxillin and phospholipase D in human breast cancer cells

Adenocarcinoma of the breast is the second leading cause of cancer mortality among women in the United States. The successful treatment of breast cancer requires greater understanding of the molecular and cellular basis of breast cancer phenotypes. A highly aggressive human breast cancer is often modeled using MDA-MB-231 cells that depend on PLD activity for survival. In response to the stress of serum withdrawal, there is increased motility and invasiveness of these cells that is associated with a rapid increase in PLD activity. In addition, PLD activity is elevated in response to most mitogenic signals. Similar to PLD, paxillin, a focal adhesion adaptor protein, and Erk, mitogen-activated protein kinase, play vital roles in cell motility through regulation of focal adhesion dynamics. However, whether these proteins work together to regulate cell motility remains unclear. In this study, we investigated the role of PLD activity on paxillin regulation, Erk activation and formation of a paxillin-Erk complex. Inhibition of PLD activity either by treatment with 1-Butanol or by dominant negative mutation led to an increase in paxillin tyrosine phosphorylation, a decrease in Erk activation, as measured by phosphorylation, and enhanced paxillin-Erk association. In addition, we found that paxillin tyrosine phosphorylation depends upon Erk activity. Taken together, these results suggest that Erk activity is governed by PLD activity and regulates the tyrosine phosphorylation of paxillin, potentially explaining its role in cell motility. This study indicated that PLD, paxillin and Erk participate in the same signaling pathway in this breast cancer cell line.