Staurosporine, a protein kinase inhibitor, stimulates cartilage differentiation by embryonic facial mesenchyme.

We have examined the effects of staurosporine, a potent inhibitor of protein kinase C, on cartilage differentiation in cultured mesenchyme of embryonic facial primordia. Mesenchymal cells from the frontonasal, maxillary, and mandibular processes and hyoid arches of stage 24/25 chicken embryos were maintained in high density micromass cell cultures in the presence or absence of 5 nM staurosporine. In cultures of frontonasal and mandibular process mesenchyme, which spontaneously developed numerous chondrogenic cell aggregates, staurosporine treatment enhanced Alcian blue-positive matrix accumulation, increased pericellular sulfated glycosaminoglycan (GAG) deposition by 5.8- and 2.7-fold, respectively, and elevated cytoplasmic levels of cartilage-specific proteoglycan mRNA. In maxillary process mesenchyme, which formed little cartilage matrix under control culture conditions, staurosporine treatment stimulated extensive cartilage nodule formation, promoted a 5.4-fold rise in matrix GAG accumulation, and increased expression of both type II collagen and cartilage proteoglycan mRNA. Moreover, staurosporine treatment initiated chondrocyte differentiation and induced the expression of type II collagen and cartilage proteoglycan gene transcripts in hyoid arch mesenchyme, which exhibited no spontaneous chondrogenesis in control cultures. The results demonstrate that staurosporine promotes cartilage formation in embryonic facial mesenchyme, and suggest the possibility that protein kinase C might function as an inhibitory modulator of chondrocyte differentiation in the neural crest-derived progenitor cells of the embryonic facial skeleton.