Pref-1 Regulates Mesenchymal Cell Commitment and Differentiation through Sox9

Pref-1 is an EGF repeat-containing transmembrane protein that produces a biologically active soluble form by TACE-mediated cleavage. Although Pref-1 inhibition of adipogenesis has been well established, the specific target(s) of Pref-1 or the Pref-1 function in mesenchymal cell commitment/differentiation are not known. Here, we show that Sox9 downregulation is required for adipocyte differentiation and that Pref-1 inhibits adipocyte differentiation through upregulating Sox9 expression. Sox9 directly binds to the promoter regions of C/EBP beta and C/EBP delta to suppress their promoter activity, preventing adipocyte differentiation. Furthermore, we also show that, by inducing Sox9, Pref-1 promotes chondrogenic induction of mesenchymal cells but prevents chondrocyte maturation as well as osteoblast differentiation, with supporting in vivo evidence in Pref-1 null and Pref-1 transgenic mice. Thus, Sox9 is a Pref-1 target, and Pref-1 directs multipotent mesenchymal cells to the chondrogenic lineage but inhibits differentiation into adipocytes as well as osteoblasts and chondrocytes.