TGFbeta protects mesoangioblasts from apoptosis via sphingosine kinase-1 regulation

Mesoangioblasts are vessel-derived progenitor cells that can be induced to differentiate into different cell types of the mesoderm such as muscle and bone. Here we examined the role of transforming growth factor-beta (TGFbeta), a pleiotropic cytokine that plays a major role in development and specifically induces smooth muscle differentiation of mesoangioblasts, in the regulation of death and survival of these cells. TGFbeta exerts a marked anti-apoptotic action in mesoangioblasts with a mechanism involving regulation of sphingosine kinase 1 (SphK1), one of the isoforms responsible for S1P formation. Treatment with the cytokine efficaciously protected mesoangioblasts from apoptosis induced by serum starvation or staurosporine treatment assessed by various means such as activation of caspase-3, determination of cytoplasmic histone-associated-DNA-fragments and PE-AnnexinV staining. The protective action of TGFbeta from staurosporine-induced apoptosis was strongly reduced when the SphK activity was inhibited by drugs, when SphK1 but not SphK2 was downregulated by specific siRNA and when a SphK1 dominant negative mutant was overexpressed. Staurosporine treatment induced down-regulation of both SphK isoforms and TGFbeta rescued SphK1 but not SphK2 expression. Interestingly, TGFbeta strongly enhanced SphK activity during staurosporine-induced cell death. Both TGFbeta-induced SphK1 up-regulation and TGFbeta anti-apoptotic action were found to be dependent on p42/44 MAPK activation.