Suppression of ADAM 10-induced Delta-1 Shedding Inhibits Cell Proliferation During the Chondro-Inhibitory Action of TGF-beta3

Although transforming growth factors (TGFs) are implicated in the process of endochondral ossification, which is initiated by the differentiation of mesenchymal cells into chondrocytes, it is not clear how TGF-beta 3 regulates the chondrogenic differentiation of limb bud mesenchymal cells. Here, differential display polymerase chain reaction (DD-PCR) screening and RT-PCR analysis revealed that transcripts of A Disintegrin And Metalloprotease 10 (ADAM 10) decreased during the chondro-inhibitory action of TGF-beta 3 on cultured chick leg bud mesenchymal cells. Electroporation of ADAM 10 morpholino antisense oligonucleotides inhibited the ectodomain shedding of delta-1, and cell proliferation and subsequent precartilage condensation, in a manner similar to that caused by TGF-beta3. The suppression of mesenchymal cell proliferation induced by TGF-beta 3 and ADAM 10 morpholino antisense oligonucleotides was reversed by activation of ADAM 10 with phorbol 12-myristate 13-acetate (PMA) or knockdown of Notch-1 with siRNA. Collectively, these data indicate that, in cultured chick leg bud mesenchyme cells, TGF-beta 3 downregulates ADAM 10 and inhibits cell proliferation and subsequent precartilage condensation by inhibiting the ectodomain shedding of delta-1, and that this results in the activation of Notch signaling.