Phospholipase D confers rapamycin resistance in human breast cancer cells

Abstract

mTOR (mammalian target of rapamycin) is a protein kinase that regulates cell cycle progression and cell growth. Rapamycin is a highly specific inhibitor of mTOR in clinical trials for the treatment of breast and other cancers. mTOR signaling was reported to require phosphatidic acid (PA), the metabolic product of phospholipase D (PLD). PLD, like mTOR, has been implicated in survival signaling and the regulation of cell cycle progression. PLD activity is frequently elevated in breast cancer. We have investigated the effect of rapamycin on breast cancer cell lines with different levels of PLD activity. MCF-7 cells, with relatively low levels of PLD activity, were highly sensitive to the growth-arresting effects of rapamycin, whereas MDA-MB-231 cells, with a 10-fold higher PLD activity than MCF-7 cells, were highly resistant to rapamycin. Elevating PLD activity in MCF-7 cells led to rapamycin resistance; and inhibition of PLD activity in MDA-MB-231 cells increased rapamycin sensitivity. Elevated PLD activity in MCF-7 cells also caused rapamycin resistance for S6 kinase phosphorylation and serum-induced Myc expression. These data implicate mTOR as a critical target for survival signals generated by PLD and suggest that PLD levels in breast cancer could be a valuable indicator of the likely efficacy of rapamycin treatment.

Defective TGF-β signaling sensitizes human cancer cells to rapamycin

“…TGF-b suppresses rapamycin-induced apoptosis N Gadir et al consideration in the use of rapamycin is that it acts competitively with PLD-generated phosphatidic acid (Foster, 2004(Foster, , 2006(Foster, , 2007 necessitating higher levels of rapamycin in cells with elevated PLD activity (Chen et al, 2003(Chen et al, , 2005. Since many cancer cells, including all of the cell lines used in this study have elevated levels of PLD activity (our unpublished results), the dose of rapamycin used will also be important for effective use in clinical settings.…”

“…Thus, the status of TGF-b signaling and PLD activity could be critical factors for determining whether rapamycin will be an effective and appropriate strategy for anti-cancer therapeutic strategies. The suppression of PLD activity could improve the efficacy of rapamycin as has been demonstrated in culture (Chen et al, 2003). The use of rapamycin in therapeutic strategies for targeting cancers has been widely discussed because it is well tolerated, it is highly specific for mTOR, and because it targets survival signals in cancer cells (Sawyers, 2003;Foster, 2004).…”

“…Equal amounts of proteins were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis on polyacrylamide-separating gels. Electrophoresed proteins were then transferred to nitrocellulose and subjected to western blot analysis as described previously (Chen et al, 2003).…”

The phospholipid code: a key component of dying cell recognition, tumor progression and host–microbe interactions

“…61 Phospholipase D overexpression has been reported for many cancer types including breast cancer cell lines and tissue samples, as well as renal and gastric cancers and is associated with mTOR-mediated pro-survival phenotypes. [62][63][64][65] Thus, modification of the intracellular phospholipid code by changes in the expression and/or activity of various phospholipid modifiers can ultimately regulate tumor progression.…”

Phorbol 12-myristate 13-acetate and serum synergize to promote rapamycin-insensitive cell proliferation via protein kinase C-eta

“…As the mTOR pathway is activated in GBM tumor samples, rapamycin and its analogs have been tested as chemotherapeutic agents in the treatment of glioblastoma. Although rapamycin and its analogs have demonstrated potential as chemotherapeutic agents in the treatment of several cancers including GBMs, recent studies suggest certain populations of cancer cells are not susceptible to rapamycin inhibition of cell proliferation (Huang and Houghton, 2001;Dilling et al, 2002;Chen et al, 2003;Gera et al, 2004;Noh et al, 2004;Galanis et al, 2005).…”