The Src family tyrosine kinases and their substrates are involved in cell-cell and cell-matrix
interactions. We found that in PC12h cells, an increase of cell density enhanced the tyrosine
phosphorylation levels of several intracellular proteins including p130 cas. Because it is a
possible substrate for Src family kinases, we measured pp60 c-src activity and found that it
was higher in high density cultures than in low density cultures. This phenomenon was also
observed in PC12 (the parental cell line of the PC12h subclone), Balb/c 3T3, Swiss 3T3, and …