Rapid modulation of the apoptosis regulatory genes, bcl-2 and bax by prolactin in rat Nb2 lymphoma cells.
The Nb2 rat lymphoma represents a useful model for investigation of molecular events coupled to PRL-induced proliferation. Moreover, recent evidence has also demonstrated the utility of this system to study mechanisms linked to programmed cell death (apoptosis). Thus, glucocorticosteroids activate apoptosis in lactogen-dependent Nb2 cells, whereas the addition of PRL abrogates this effect. The present study was conducted to determine whether PRL stimulation in lactogen-dependent Nb2-11 or autonomous Nb2-SFJCD1 cultures alters expression of bcl-2 or bax, genes that suppress or facilitate apoptosis, respectively. We demonstrate that PRL stimulation in stationary Nb2-11 cultures significantly increased the level of bcl-2 messenger RNA (mRNA) within 3 h (15-fold) and its protein product by 6 h, time points previously shown to correspond with G1 cell cycle progression. In Nb2-SFJCD1 cells, bcl-2 mRNA was found to be constitutively present. Addition of PRL to these lactogen-independent cultures further enhanced its expression at the mRNA and protein levels with a kinetic pattern similar to that observed in the PRL-dependent line. Results from stability studies indicated that increased bcl-2 mRNA evoked by PRL in Nb2 cell lines was most likely not attributable to increased stability of its transcripts. Furthermore, the rapid increase in its expression in PRL-stimulated Nb2-11 cells was not altered by inhibition of protein synthesis suggesting a direct action of the hormone. PRL also increased bax mRNA by 8 h in Nb2-11 cultures. However, hormone stimulation markedly attenuated the level of the Bax protein from 2-6 h. In contrast, bax expression in Nb2-SFJCD1 cultures remained unaltered by the addition of the hormone. These results demonstrate that altered expression of bcl-2 and bax are each associated with PRL-stimulated cell cycle progression in Nb2 cells. Moreover, bcl-2 appears to be an immediate-early gene induced by PRL in the hormone-dependent line and may represent an important regulator of early G1 cell cycle progression most likely by suppressing cell death mechanisms.
Leff
M A
MA
Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202-9037, USA.
Buckley
D J
DJ
Krumenacker
J S
JS
Reed
J C
JC
Miyashita
T
T
Buckley
A R
AR
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D003513:Cycloheximide / Q000494:pharmacology; D004355:Drug Stability; D015870:Gene Expression / Q000187:drug effects*; D005809:Genes, Regulator; D019254:Genes, bcl-2; D006801:Humans; D008223:Lymphoma / Q000235:genetics / Q000473:pathology; D051379:Mice; D011388:Prolactin / Q000494:pharmacology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D013997:Time Factors; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein
C494826:BAX protein, human; C494827:Bax protein, mouse; C494828:Bax protein, rat; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D011388:Prolactin; D003513:Cycloheximide