Prolactin-stimulated mitogenesis of cultured astrocytes.

PRL has been reported to activate cell cycle-specific enzyme markers in nonreproductive tissues. To determine if PRL stimulates cell cycle-specific markers and cell growth in the central nervous system, the effect of PRL on cellular proliferation was examined in cultured astrocytes. Astrocytes from confluent cultures were plated onto glass slides at a density of 2 x 10(4) cell/ml 24 h before use. In some experiments, cells were serum deprived for 24 h (Go-arrested) after plating. Cell proliferation was examined directly by an increase in cell number and in individual cells by immunofluorescent detection of proliferating cell nuclear antigen (PCNA) and the incorporation of 5-bromo-2'-deoxyuridine (BrUd). When incubated with 1% serum, a small percentage (less than 5%) of the cells expressed PCNA. In cells cultured with rat PRL (10(-10)-10(-7) M) for 18 h, staining of PCNA increased in a dose-dependent manner, with maximal expression occurring at 10(-9) M PRL. At concentrations above 10(-9) M, PCNA staining decreased. To examine the specificity of the PRL-induced increase in PCNA, cells were incubated in the presences of 10(-9) M rat (r) or bovine (b) GH. Whereas incubation of astrocytes with rPRL and bPRL activated PCNA, cells incubated with either rGH or bGH showed only a slight increase in the number of cells expressing PCNA. Further, incubation of astrocytes with 1 nM PRL in the presence of 100 nM cyclosporine, an immunosuppressive agent that specifically displaces PRL from its receptor, decreased the percentage of nuclei stained for PCNA to that observed in non-PRL-stimulated controls. Transient exposure of cells to 10(-9) M PRL for 30 min resulted in an increase in the number of cells expressing PCNA when cultured for 18 h in the presence of 1% serum. In the presence of 1% serum, 10(-9) M PRL increased the incorporation of BrUd and resulted in a 3-fold increase in the doubling rate. In cells incubated in serum-free medium, only a few PCNA-positive cells could be detected. Treatment of Go-arrested astrocytes with PRL (10(-10)-10(-7) M) for 18 h resulted in a dose-dependent increase in the expression of PCNA. PCNA-positive cells were detected in cultures incubated with 10(-11) M PRL, with maximal expression at 10(-9) M.(ABSTRACT TRUNCATED AT 400 WORDS)