Pasteurella multocida toxin (PMT) activates the ERK signaling pathway, in part, by upregulating CTGF expression

Abstract

PMT, a 146 kDa bacterial protein, is a potent mitogen and a strong inducer of anchorage‐independent growth for fibroblast and osteoclast cells. We showed that PMT activated the ERK pathway, and that this ERK activation was also detected when quiescent 3T3 cells were treated with conditioned media taken from PMT‐treated cells. These results support the existence of a diffusible factor(s) that mediates ERK activation. Microarray analysis revealed that connective tissue growth factor (CTGF) is the most elevated factor in PMT‐treated cells. CTGF is a 36‐kDa secreted protein and a member of the CCN family. It stimulates cellular proliferation and regulation of angiogenesis and tumorigenesis. Western blot analysis using CTGF antibody revealed a robust elevation of an immunoreactive protein of 36–38 kDa in both cell lysate and conditioned media of PMT‐treated cells. This observed PMT‐induced CTGF elevation was also detected in WT, but not in Gαq/Gα11‐deficient MEF cells. While PMT failed to induce ERK activation in Gαq/Gα11‐deficient MEF cells, the conditioned media can activate ERK in these cells suggesting that PMT upregulates the CTGF protein level and leads to ERK activation.This work was supported, in part, by the Intramural Research Program of the NIH, NHLBI.