ABSTRACT
The results of several recent studies have indicated that protein kinase C (PKC) may be involved in the prolactin (PRL) stimulation of mitogenesis in the Nb2 node lymphoma cell line. The PKC activator 12-O-tetradeconylphorbol-13-acetate (TPA) at certain concentrations has been shown to potentiate the mitogenic effect of PRL, whereas at higher concentrations, TPA inhibits the PRL response. Several inhibitors of PKC have also been shown to impair the PRL stimulation of metabolic process in the Nb2 cells. These studies provide further evidence for the likely involvement of PKC in the PRL stimulation of mitogenesis in the Nb2 cells. A transient, time-dependent accumulation of PKC in the particulate fraction of the Nb2 cells is observed in response to PRL. TPA is also shown to elicit a similar effect, albeit at a much earlier time and with a greater magnitude. On long-term exposure (3 days), high concentrations of TPA down-regulate the PKC enzyme; this down-regulation likely accounts for the inhibitory effect of high concentrations of TPA on the PRL stimulation of cell division. In further studies, the PKC inhibitors H-7 and gossypol were shown to inhibit the PRL stimulation of cell division in a concentration-dependent fashion.
Subject(s)
Cell Division/drug effects , Lymphoma/pathology , Prolactin/pharmacology , Protein Kinase C/metabolism , Tumor Cells, Cultured/cytology , 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine , Animals , Cell Line , Gossypol/pharmacology , Isoquinolines/pharmacology , Kinetics , Lymphoma/enzymology , Piperazines/pharmacology , Prolactin/physiology , Protein Kinase C/antagonists & inhibitors , Rats , Tetradecanoylphorbol Acetate/pharmacology , Tumor Cells, Cultured/drug effects , Tumor Cells, Cultured/enzymologyABSTRACT
Specific aspects of the prolactin stimulation of RNA, DNA and protein synthesis in the Nb2 node lymphoma cell line were determined. In time sequence studies the onset of the prolactin stimulation of the incorporation of radiolabeled precursors into these macromolecules was found to be 0.5-1 h for [3H]uridine incorporation into RNA, 1-2 h for [3H]leucine incorporation into protein, and 4-8 h for [3H]thymidine incorporation into DNA. The total DNA content of the cell cultures was increased by 12-18 hours after addition of prolactin. Amiloride, an inhibitor of the plasma-membrane-bound Na+/H+ antiporter, was found to inhibit the mitogenic effects of prolactin. Amiloride was also found to inhibit the prolactin stimulation of DNA, RNA and protein synthesis, thus suggesting that the initial regulation of the Na+/H+ antiporter may initiate these responses as well as the mitogenic effect of prolactin. In contrast, H-7, a drug which inhibits protein kinase C, had no effect on the magnitude of the prolactin stimulation of DNA, RNA or protein synthesis at a drug concentration (100 muM) that abolished the mitogenic effect of prolactin. The early effects of prolactin on RNA, DNA and protein synthesis would therefore appear not to involve an activation of protein kinase C.
Subject(s)
DNA, Neoplasm/biosynthesis , Lymphoma/metabolism , Neoplasm Proteins/biosynthesis , Prolactin/pharmacology , RNA, Neoplasm/biosynthesis , 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine , Amiloride/pharmacology , Carrier Proteins/physiology , Cell Division/drug effects , Isoquinolines/pharmacology , Piperazines/pharmacology , Protein Kinase Inhibitors , Protein Kinases/metabolism , Sodium-Hydrogen Exchangers , Time Factors , Tumor Cells, CulturedABSTRACT
These studies provide further support for the thesis that the activation of protein kinase C is likely involved in the prolactin (PRL) stimulation of mitogenesis in the Nb2 node lymphoma cell line. The diterpene mezerein is shown to potentiate the mitogenic effect of PRL at a hormone concentration which elicits a less than maximum response. A similar response was observed with two diglycerides, diolein and dicaprin. Neither mezerein nor the diglycerides affected the magnitude of response to a maximum stimulatory concentration of PRL.
