Alternative splicing of type II procollagen pre-mRNA in chondrocytes is oppositely regulated by BMP-2 and TGF-β1

Type II collagen is the major protein of cartilage and is synthesized as a procollagen in two forms (IIA and IIB), generated by differential splicing of the gene primary transcript. Previous studies have indicated that only type IIB is expressed in differentiated chondrocytes. Here, we examined the effects of bone morphogenetic protein (BMP)-2 and transforming growth factor (TGF)-β1 on the expression of IIA and IIB forms expressed in de-differentiated chondrocytes grown in monolayer. Our results demonstrate that BMP-2 favors expression of type IIB whereas TGF-β1 potentiates expression of type IIA induced by subculture. These observations reveal the specific capability of BMP-2 to reverse the de-differentiation state of chondrocytes.