Serum and growth factors regulate expression of a 43 kDa protein in smooth muscle cell cultures

Smooth muscle cells respond to injury and the presence of serum factors by modulating from a quiescent contractile cell to a motile synthetic phenotype. To evaluate the biochemical response to serum exposure, we examined the proteins synthesized and secreted in response to serum. The most prominent effect of serum was the rapid production of a protein with an apparent molecular weight of 43 kDa. Removal of serum from the culture environment led to a cessation of 43 kDa protein production. The effect of exogenous heparin on 43 kDa protein production was also evaluated. Neither the 43 kDa protein nor a previously described 38 kDa protein was induced by heparin. Further, heparin treatment did not counteract the effects of serum. These studies demonstrate that an early response of vascular smooth muscle cells to serum is the production of this previously undescribed protein and that other modifications of the culture conditions did not affect its synthesis.