Extracellular matrix metalloproteinase inducer (EMMPRIN) is a cell surface glycoprotein enriched on tumor cells and normal epithelia. It is mainly known for its ability to induce matrix metalloproteinase production in fibroblasts following epithelial-stromal interaction. We sought to examine whether EMMPRIN has a broader role promoting fibroblast-to-myofibroblast differentiation. Because -smooth muscle actin (SMA) is considered a marker of this differentiation process, we analyzed the effect of EMMPRIN on its expression in corneal and skin fibroblasts by Western blots, immunocytochemistry, and a functional assay of collagen lattice contraction. Increasing EMMPRIN expression by cDNA transfection or by treatment with exogenously added recombinant EMMPRIN resulted in an up-regulation of SMA expression. EMMPRIN also increased the contractile properties of the treated fibroblasts as demonstrated by the immunohistochemical appearance of stress fibers and by the accelerated contraction of fibroblast-embedded collagen lattices. Blocking EMMPRIN expression by small interfering RNA inhibited SMA and collagen gel contraction induced not only by EMMPRIN but also by transforming growth factor-, a major mediator of myofibroblast differentiation that also regulated EMMPRIN expression. These findings, combined with the fact that EMMPRIN and SMA colocalized to the same cells in the stroma of pathological corneas, expand on the mechanism by which EMMPRIN remodels extracellular matrix during wound healing and cancer.—Huet, E., Vallée, B., Szul, D., Verrecchia, F., Mourah, S., Jester, J. V., Hoang-Xuan, T., Menashi, S., Gabison, E. E. Extracellular matrix metalloproteinase inducer/CD147 promotes myofibroblast differentiation by inducing -smooth muscle actin expression and collagen gel contraction: implications in tissue remodeling.