Increased expression of pp60c-src in gastric mucosa of aged rats.

The relationship between proliferative activity and the expression of pp60c-src in gastric mucosa (oxyntic gland area) of young (4-month) and aged (24-month) Fischer 344 rats was examined. Gastric mucosal proliferative activity, as assessed by 5-bromo-2'-deoxyuridine (BrdU) immunoreactive cells, was found to be 115% (p < .001) higher in aged than in young rats. This was associated with a 47% rise (p < .025) in overall tyrosine kinase (Tyr-k) activity and a 5-7-fold increase in autophosphorylation of four prominent protein bands with M(r) of 40, 55, 60, and 70 kDa in gastric mucosal membranes. A similar phenomenon was also observed for Tyr-k activity of pp60c-src in that the aged rats revealed a 69% (p < .025) higher enzyme activity and a 5-fold rise in the extent of autophosphorylation of this protein when compared with the corresponding values from young animals. Increased Tyr-k activity of pp60c-src in the gastric mucosa of aged rats could in part be due to higher levels of this protein because the relative concentration of pp60c-src, as assessed by Western blot analysis, showed a 2-5-fold increase over the young animals. In addition, the relative concentration of c-src mRNA in the gastric mucosa of aged rats was also found to be 5-6-fold higher than in young animals. We suggest that pp60c-src may play a role in regulating gastric mucosal proliferative processes in the gastric mucosa of aged rats.