Protein kinase C heterogeneity in GH4C1 rat pituitary cells. Characterization of a Ca2(+)-independent phorbol ester receptor.
Clonal GH4C1 rat pituitary cells are heterogeneous with respect to phorbol dibutyrate receptors (PDBu-R) and protein kinase C (PKC) content. GH cell PDBu-Rs can be separated into two categories based on Ca2(+)-modulation of receptor affinity. Approximately 70% of the cytosolic PDBu-Rs demonstrate Ca2(+)-sensitive receptor affinity and redistribute from the soluble to the particulate fraction in the presence of excess Ca2+. The other 30% of the receptors remain in the cytosol in the presence of excess Ca2+. Their receptor affinity is Ca2(+)-independent. Northern blot hybridization and immunoblot analysis showed that GH4C1 cells express Ca2(+)-independent epsilon-PKC as well as Ca2(+)-dependent alpha- and beta-PKCs. Cell lysis in Ca2+ caused the redistribution of greater than 95% of alpha- and beta-PKC to the particulate fraction, whereas approximately 90% of the epsilon-PKC remained in the cytosol. In contrast, brief treatment of GH cell cultures with PDBu or thyrotropin-releasing hormone caused redistribution of all three isozymes. Prolonged treatment with PDBu down-modulated all three isozymes but at different rates and to different extents. In contrast, prolonged thyrotropin-releasing hormone treatment selectively down-modulated epsilon-PKC. These results demonstrate that GH cells have both Ca2(+)-sensitive and -insensitive PKCs and PDBu-Rs and that both populations are regulated by agonists that control prolactin synthesis and secretion by these cells.
Kiley
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W. Alton Jones Cell Science Center, Inc., Lake Placid, New York 12946.
Schaap
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D
Parker
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P
Hsieh
L L
LL
Jaken
S
S
D000818:Animals; D029742:Caenorhabditis elegans Proteins; D002118:Calcium / Q000494:pharmacology*; D002352:Carrier Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D007527:Isoenzymes / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D007700:Kinetics; D010743:Phospholipids / Q000494:pharmacology; D010902:Pituitary Gland; D011493:Protein Kinase C / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011955:Receptors, Drug / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D007527:Isoenzymes; D010743:Phospholipids; D012333:RNA, Messenger; D011955:Receptors, Drug; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D011493:Protein Kinase C; D002118:Calcium