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Gα13 Stimulates Rho-dependent Activation of the Cyclooxygenase-2 Promoter*

Cyclooxygenase-2 (COX-2) gene expression is rapidly increased by cytokines, tumor promoters, and growth factors and is markedly enhanced in various cancer cells. Here, we examine the regulation of COX-2 promoter activity by α subunits of heterotrimeric G proteins in NIH 3T3 cells. Using a transient transfection assay with a reporter vector in which the murine COX-2 promoter drives the production of luciferase and expression vectors encoding for α subunits of G-proteins, we show that overexpression of wild type and constitutively active Gα13 and Gαqinduced transcription from the COX-2 promoter. The highest level of induced luciferase activity (5.8-fold) occurred in cells expressing the constitutively active Gα13(Q226L). We also show that expression of a constitutively active mutant of Rho (RhoQ63L) also induced transcription from the COX-2 promoter. Co-expression ofClostridium botulinum C3 toxin specifically blocked induction of the COX-2 promoter by either Gα13Q226L or RhoQ63L but did not prevent the activation of this promoter by Ras, Rac, v-src, or forskolin. We conclude that Gα13 signals through a Rho-dependent pathway leading to activation of the COX-2 promoter. This pathway is not inhibited by either cytochalasin D, which disrupts actin filament organization, or genistein, a broad spectrum tyrosine kinase inhibitor, indicating a bifurcation of the signaling pathway used by Gα13/Rho to induce COX-2 expression from that used to induce stress fiber formation and tyrosine phosphorylation of focal adhesion proteins.