Vol. 60, Issue 4, 674-680, October 2001

Activation of Phospholipase C Induces the Expression of the Multidrug Resistance (MDR1) Gene through the Raf-MAPK Pathway

Jin-Ming Yang, Andrew D. Vassil, and William N. Hait

The Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey/Robert Wood Johnson Medical School, Departments of Medicine and Pharmacology, New Brunswick, New Jersey

Resistance to multiple, unrelated cancer chemotherapeutic drugs can be mediated by P-glycoprotein, the MDR1 gene product. Numerous substances, including chemotherapeutic drugs, heavy metals, growth factors, activated oncogenes, or changes in temperature increase MDR1 gene expression. Because several of these factors regulate cellular function through the activation of phospholipase C (PLC), we postulated that PLC-mediated signaling could be central to regulating the expression of MDR1. Transfection of NIH 3T3 cells with a pMJ30-PLC-1 expression vector increased the activity of the MDR1 promoter by 2- to 10-fold. PLC-mediated activation required a region between 106 and 99 of the MDR1 promoter. Treatment of cotransfected cells with platelet-derived growth factor further enhanced the activity of the MDR1 promoter. The stimulatory effect of PLC on the MDR1 promoter was increased by cotransfection with constitutively active v-raf and was blocked by the dominant-negative mutant, c-Raf-C4. The activity of mitogen-activated protein kinase (MAPK) was also increased in PLC-1-transfected cells. Furthermore, PD-98059 and U0126, two MAPK inhibitors, blocked PLC-1-induced expression of MDR1. The results of Northern blot analysis showed that activation of PLC by heat shock and growth factors increased expression of endogenous MDR1 mRNA in human renal carcinoma cells. These effects were blocked by inhibitors of the PLC-MAPK pathway. In summary, our results indicate for the first time that activation of PLC by a variety of cellular stimuli can regulate the expression of MDR1 and that the transcriptional modulation of MDR1 expression by PLC is mediated by the Raf-MAPK pathway.