Okadaic acid mimics several proximal effects of prolactin in Nb2 lymphoma cells.
We previously reported that prolactin-mediated macromolecular synthesis and mitogenesis are coupled to the activation of mitogen-activated protein kinase (MAPK) and p70 S6-kinase (p70S6K). Full activation of MAPK requires tyrosine and threonine phosphorylation whereas that of p70S6K requires serine phosphorylation. In the present study, okadaic acid, which inhibits serine/threonine protein phosphatase activity, was used to explore the linkage of MAPK and p70S6K activation to down-stream effects of prolactin in Nb2 cells. The results show that 1 nM okadaic acid augmented prolactin-stimulated mitogenesis and synthesis of protein and DNA 250%, 42%, and 70%, respectively. Addition of okadaic acid alone a) stimulated and sustained p70S6K activity (5- to 8-fold) and MAPK (3.5- to 5-fold); and b) increased protein synthesis with the maximum effect being about equal to that of prolactin (2.1-fold with 1 nMokadaic acid versus 2.3-fold with 0.2 nMprolactin). However, okadaic acid did not affect DNA synthesis or mitogenesis. These results indicate that the activation of MAPK and p70S6K is necessary for stimulation of protein synthesis but not sufficient for prolactin-driven mitogenesis.
Carey
G B
GB
Department of Biochemistry and Molecular Biophysics, Medical College of Virginia Campus, Virginia Commonwealth University, Richmond 23298-0614, USA.
Liberti
J P
JP
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008223:Lymphoma / Q000201:enzymology; D008938:Mitosis / Q000187:drug effects / Q000502:physiology; D018716:Molecular Mimicry; D019319:Okadaic Acid / Q000494:pharmacology*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D011388:Prolactin / Q000494:pharmacology*; D014176:Protein Biosynthesis; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000187:drug effects
D004273:DNA, Neoplasm; D004791:Enzyme Inhibitors; D019319:Okadaic Acid; D011388:Prolactin; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases