The co-mitogenic combination of transforming growth factor beta 1 and bombesin protects protein kinase C-delta from late-phase down-regulation, despite synergy in diacylglycerol accumulation.
Bombesin induces the down-regulation of protein kinase C-delta (PKC-delta) and PKC-epsilon in Swiss 3T3 cells. Simultaneous addition of transforming growth factor beta 1 (TGF beta 1) selectively blocks PKC-delta down-regulation at mid-S-phase, whereas PKC-epsilon levels continue to decline. Northern blot analysis shows that PKC-epsilon levels could be controlled in part at the level of transcription; PKC-delta mRNA levels remained constant at these later times. Bombesin induces a sustained elevation of some species of diacylglycerol (DAG), consistent with the observed loss of PKC-delta and PKC-epsilon. Interestingly, the combination of bombesin and TGF-beta 1 produces an even greater DAG response. Flow cytometric analysis demonstrates that bombesin induces only 15% of the cells to enter the cell cycle, in contrast to the combination of TGF beta 1 plus bombesin which induces 75-80% of the cells to progress through the cycle. The protection of PKC-delta from down-regulation under conditions of sustained DAG elevation correlates with the mitogenic response and implies that the down-regulation process itself is regulated. Consistent with this, it is demonstrated that bombesin plus TGF beta 1 protects PKC-delta from phorbol ester-induced down-regulation.
Olivier
A R
AR
Protein Phosphorylation Laboratory, Imperial Cancer Research Fund, London, U.K.
Hansra
G
G
Pettitt
T R
TR
Wakelam
M J
MJ
Parker
P J
PJ
D016475:3T3 Cells; D000818:Animals; D015152:Blotting, Northern; D001839:Bombesin / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004075:Diglycerides / Q000378:metabolism; D004347:Drug Interactions; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007527:Isoenzymes / Q000096:biosynthesis; D007700:Kinetics; D051379:Mice; D011493:Protein Kinase C / Q000096:biosynthesis*; D064546:Protein Kinase C beta; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D012333:RNA, Messenger / Q000096:biosynthesis; D016196:S Phase; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D004075:Diglycerides; D007527:Isoenzymes; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; C497259:Prkcd protein, mouse; C497256:Prkce protein, mouse; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D051745:Protein Kinase C-delta; D051744:Protein Kinase C-epsilon; D001839:Bombesin