Phospholipase D Couples Survival and Migration Signals in Stress Response of Human Cancer Cells

Abstract

MDA-MB-231 human breast cancer cells belong to a highly invasive metastatic cell line that depends on phospholipase D (PLD) activity for survival when deprived of serum growth factors. In response to the stress of serum withdrawal, there is a rapid and dramatic increase in PLD activity. Concomitant with increased PLD activity, there was an increase in the ability of MDA-MB-231 cells to both migrate and invade Matrigel TM . The ability of MDA-MB-231 cells to both migrate and invade Matrigel TM was dependent on both PLD and mTOR, a downstream target of PLD signals. Serum withdrawal also led to a PLD-dependent increase in the expression of the stress factor, hypoxia-inducible factor-1␣. These data reveal that PLD survival signals not only prevent apoptosis but also stimulate cell migration and invasion, linking the ability to suppress apoptosis with the ability to metastasize.The conversion of a normal cell to a malignant cancer cell involves multiple genetic alterations that overcome the many protections built into cells that prevent unwanted proliferation (1). Perhaps the most crucial step in progression to malignancy is gaining the ability to migrate or metastasize to distant sites where the growth of multiple tumors ultimately causes the lethal consequences of the cancer. Although there are several cellular properties that correlate with increased metastatic potential, such as increased protease secretion (2), there has never been a clear genetic event that confers metastatic capability. However, it has been suggested that mutations occurring at early stages of tumorigenesis that confer a proliferative advantage may also contribute to the ability to metastasize at later stages of tumor progression (3).Among the obstacles to be overcome in a developing tumor are default apoptotic programs that cause cells with faulty division signals to undergo apoptosis (1). A cell must generate "survival signals" to suppress these apoptotic programs (4 -6). Interestingly, signals that have been shown to suppress apoptosis have also been linked to cell migration, a hallmark of the metastatic phenotype. Both phosphatidylinositol 3-kinase and phospholipase D (PLD), 2 which provide survival signals in human cancer cells (7-9), have also been linked with cellular processes that contribute to cell migration (8,10). This correlation between survival and cell migration suggests that generating a survival signal early in tumorigenesis could also endow the cell with the ability to migrate. This raises the question as to how the migration would be triggered. One possibility is that although a primary tumor mass is forming, survival signals are selected for in cells deprived of blood serum to suppress the apoptosis that would occur in an unvascularized tumor mass. If the survival response of cells also includes increased cell migration, then in addition to suppression of apoptosis, the response would also include migration to sites where growth factors and nutrition could be obtained.We recently described a survival signal in the highly m...

Phospholipase D provides a survival signal in human cancer cells with activated H-Ras or K-Ras

“…1, both the T24 and Calu-1 cells express levels of PLD activity that were substantially higher than that observed in the MBA-MB-231 cells. The MDA-MB-231 cells represent an aggressive malignant cancer cell line that migrates in culture, whereas the MCF-7 cells represent a benign cancer cell line that does not migrate in culture [24]. The ability of the MDA-MB-231 cells to migrate in culture was dependent on PLD activity [24].…”

“…The T-24 bladder carcinoma expresses an activated H-Ras gene [19,20] and Calu-1 lung carcinoma cells express an activated K-Ras gene [21]. The PLD activity in these two cell lines was evaluated and compared with the PLD activity in two breast cancer cell lines (MDA-MB-231 and MCF7), which express relatively high and low PLD activity respectively [23,24]. As shown in Fig.…”

“…The MDA-MB-231 cells represent an aggressive malignant cancer cell line that migrates in culture, whereas the MCF-7 cells represent a benign cancer cell line that does not migrate in culture [24]. The ability of the MDA-MB-231 cells to migrate in culture was dependent on PLD activity [24]. Thus, the observation that these two human cancer cell lines with activating mutations in either H-Ras or K-Ras have substantially elevated levels of PLD activity may contribute to their malignant capacity.…”

shRNA Mediated RHOXF1 Silencing Influences Expression of BCL2 but not CASP8 in MCF-7 and MDA-MB-231 Cell Lines

“…MCF-7 is believed to have a relatively benign phenotype, while MDA-MB-231 human breast cancer cells are a highly invasive metastatic cell line. Expression profile of these 2 cell lines have been compared with specific focus on genes related to metastasis, cell motility and apoptosis (Zheng et al, 2006). MDA-MB-231 cells have shown to have a much more malignant molecular profile than MCF-7 cells with regard to expression of genes having functions in cell migration and invasion, the ability to suppress apoptosis and the ability to metastasize (Zheng et al, 2006).…”

“…Expression profile of these 2 cell lines have been compared with specific focus on genes related to metastasis, cell motility and apoptosis (Zheng et al, 2006). MDA-MB-231 cells have shown to have a much more malignant molecular profile than MCF-7 cells with regard to expression of genes having functions in cell migration and invasion, the ability to suppress apoptosis and the ability to metastasize (Zheng et al, 2006). The significant higher expression of RHOXF1 in MDA-MB-231 than in MCF-7 implies a role for this gene in malignant phenotype, especially when considering the antiapoptotic role of RHOXF1 in germ cells.…”