Alterations in pim-1 and c-myc expression associated with sodium butyrate-induced growth factor dependency in autonomous rat Nb2 lymphoma cells.
Whereas Nb2-11 lymphoma cells critically require prolactin (PRL) for growth, Nb2-SFJCD1 subline cells are growth factor independent. Treatment with the differentiating agent, sodium butyrate (NaBT), has been demonstrated previously to lead to growth arrest of Nb2-SFJCD1 cells and a transient reversion to PRL growth requirement following removal of NaBT. In the present study, the relation of NaBT-induced growth arrest to the cell cycle was examined using flow cytometry, and the effect of PRL on expression of the immediate-early proto-oncogenes, pim-1 and c-myc, in NaBT-pretreated cultures was evaluated. Treatment of Nb2-SFJCD1 cells with 2 mM NaBT for 72 h caused growth arrest in the majority of the cells in the G1 phase of the cell cycle, an effect similar to that produced by lactogen deprivation in PRL-dependent Nb2 cultures. The addition of PRL stimulated a concentration-dependent re-entry into the cell cycle. In other experiments, NaBT treatment significantly reduced the steady-state levels of pim-1 and c-myc mRNA. Stimulation with PRL induced a rapid and concentration-dependent biphasic accumulation of each mRNA with similar kinetics. Maximal expression of both proto-oncogenes occurred within 2-4 h and after 12 h. Results from mRNA stability studies suggest that the observed increases in expression of pim-1 and c-myc most likely do not reflect increased stability of the transcripts. The results indicate that NaBT-induced differentiation in autonomous Nb2-SFJCD1 causes growth arrest of the cells in the G1 phase of the cell cycle and reduces the basal levels of pim-1 and c-myc mRNAs. Mitogenic stimulation with PRL reinitiates cell cycle progression characterized by biphasic expression of each proto-oncogene. It is suggested that NaBT is a useful tool for investigation of the malignant progression from growth factor dependency to autonomy in the Nb2 lymphoma paradigm.
Buckley
A R
AR
Department of Pharmacology and Toxicology, University of North Dakota School of Medicine, Grand Forks 58202-9037, USA.
Leff
M A
MA
Buckley
D J
DJ
Magnuson
N S
NS
de Jong
G
G
Gout
P W
PW
D000818:Animals; D015152:Blotting, Northern; D002087:Butyrates / Q000494:pharmacology*; D020148:Butyric Acid; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D005434:Flow Cytometry; D016193:G1 Phase / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000502:physiology; D006133:Growth Substances / Q000494:pharmacology; D056572:Histone Deacetylase Inhibitors; D016399:Lymphoma, T-Cell; D011388:Prolactin / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D051573:Proto-Oncogene Proteins c-pim-1; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D014407:Tumor Cells, Cultured / Q000166:cytology / Q000187:drug effects / Q000201:enzymology
D002087:Butyrates; D006133:Growth Substances; D056572:Histone Deacetylase Inhibitors; D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D020148:Butyric Acid; D011388:Prolactin; C496637:Pim1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051573:Proto-Oncogene Proteins c-pim-1