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Prolactin‐Stimulated Mitogenesis of Cultured Astrocytes Is Mediated by a Protein Kinase C‐Dependent Mechanism
Author(s) -
DeVito William J.,
Avakian Crystal,
Stone Scott,
Okulicz William C.
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb03227.x
Subject(s) - protein kinase c , biology , prolactin , staurosporine , endocrinology , cell growth , medicine , cytosol , microbiology and biotechnology , signal transduction , cell culture , tetradecanoylphorbol acetate , biochemistry , enzyme , hormone , genetics
Prolactin (PRL) has been reported to activate cellular proliferation in nonreproductive tissue, such as liver, spleen, and thymus. Recently, we have extended the possible role of PRL as a mammalian mitogen by demonstrating a mitogenic effect of PRL in cultured astrocytes. Although the cellular mechanisms by which PRL regulates cell growth are not fully understood, protein kinase C (PKC) has been implicated as one of the transmembrane signaling systems involved in the regulation of PRL‐induced cell proliferation in Nb2 lymphoma cells and liver. In the present studies, we examined the possible role of PKC in PRL‐induced proliferation of cultured astrocytes. Incubation of cultured astrocytes with 1 n M PRL resulted in a rapid translocation of PKC from the cytosol to the membrane, with maximal PKC activity in the membrane occurring 30 min after exposure to PRL. Translocation of PKC activity occurred over a physiological range of PRL, with maximal PKC activation occurring at 1 n M . At concentrations greater than 10 n M PRL, there was a decrease in the amount of PKC activity associated with the membrane fraction compared with that of cells stimulated with 1 n M PRL. Incubation of astrocytes with PRL in the presence of the PKC inhibitors staurosporine, 1‐(‐5‐isoquinolinesulfonyl)‐2‐methylpiperazine, or polymyxin B blocked the PRL‐induced increase in cell number with IC 50 values of approximately 2 n M , 10 μ M , and 6 μ M , respectively. PKC is the only known cellular receptor for 12‐ O ‐tetradecanoylphorbol 13‐acetate (TPA), which stimulates the translocation of PKC from the cytosol to the membrane. Incubation of astrocytes with 20 n M TPA resulted in an increase in the expression of proliferating cell nuclear antigen and cell number, whereas 4α‐phorbol 12,13‐didecanoate, an inactive phorbol ester, was ineffective. To examine further the effect of TPA and PRL on cellular proliferation, cultured astrocytes were incubated with increasing concentrations of TPA in the presence or absence of a minimal effective dose of PRL (100 p M ). In the absence of PRL, incubation with TPA resulted in an inverted U‐shaped dose‐response curve, with 100 n M TPA resulting in a maximal increase in cell number. In the presence of 100 p M PRL, the TPA dose‐response curve was shifted to the left, with maximal activity occurring with 10 n M TPA. Chronic stimulation of astrocytes with 500 n M TPA depleted the cells of PKC and blocked the PRL‐induced increase in cell number. Finally, TPA treatment decreased cell‐surface binding of 125 I‐PRL. These data indicate that the PKC is involved in the mitogenic effect of PRL in cultured astrocytes.