Alkali-resistant protein phosphorylation and tyrosine kinase activity of epithelial cell types from normal and metaplastic canine prostates

Abstract

To determine how functional changes such as growth and differentiation in the prostatic epithelium would alter protein phosphorylation on tyrosyl residues, differentiated (secretory) and basal (non-secretory) prostatic epithelial cells from normal and from metaplastic canine prostates were labeled with [ 32P]phosphate and their alkali-resistant phosphoproteins were analyzed by autoradiography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The tyrosine protein kinase activity of the cells was also assayed by phosphorylation of a synthetic substrate, poly(Glu 80-NaTyr 20), in the presence of [γ- 32p]ATP. The prostates were characterized by tissue morphology and the cells by their density on Percoll gradients and [ 3H]thymidine incorporation into DNA. In prostates from intact dogs, tall coluninar secretory epithelial cells were predominant and the non-secretory or basal epithelial cells were quiescent and did not incorporate [ 3H]thymidine. In metaplastic glands obtained from estrogen-treated castrated dogs, most of the isolated cells were non-secretory and synthesized DNA. Alkali-resistant phosphoproteins were present in all cell types. Except for two common phosphoproteins, p44 and p82, the relative phosphoprotein distribution within the gel differed when normal prostatic cells were compared to the metaplastic cells. However, the phosphoprotein patterns were the same in secretory and non-secretory cells from the same prostate tissue. On the other hand, the relative labeling intensity of phosphoproteins was always higher in non-secretory cells compared to corresponding secretory cells. Accordingly, tyrosine protein kinase (TPK) activity, expressed on a cell basis, was also higher in non-secretory cells; the ratios of TPK activities, non-secretory over corresponding secretory cells, was always higher than unity for all preparations but overlapped when cells from metaplastic glands were compared to those isolated from normal prostates. Thus, non-secretory epithelial cells isolated from either normal or metaplastic glands have a higher ability than corresponding secretory cells to phosphorylate endogenous alkali-resistant phosphoproteins and their TPK activity, measured with the synthetic substrate poly(Glu 80-NaTyr 20), is also higher.