Mechanisms of deregulation of IFN regulatory factor-1 in ras-transformed fibroblasts.
Interferon (IFN) regulatory factor-1 (IRF-1) deregulation in ras-transformed mouse fibroblasts (RS485) was studied. Treatment with the proteasome inhibitor MG132 did not alter the constitutive IRF-1 protein levels in RS485 but significantly increased them in nontransformed NIH 3T3 cells at 4 h after serum stimulation of synchronized cultures. Because IRF-1 protein levels in NIH 3T3 are minimal at 4 h after serum starvation, the cyclic expression of IRF-1 in NIH 3T3 appears to be partially due to proteasome activity; however, proteasome activity in RS485 did not appear to be defective. In NIH 3T3 and RS485 cells treated with cycloheximide, there were similar rapid drops in IRF-1 protein levels, and the addition of MG132 along with cycloheximide prevented protein loss in both cell lines. Northern blot analyses of synchronized cultures showed that the IRF-1 message closely mirrored the protein expression pattern in both NIH 3T3 and RS485 cells. In synchronized cells treated with the transcription inhibitor actinomycin D, IRF-1 mRNA half-life was only marginally longer in ras-transformed fibroblasts than in the nontransformed cells, and this difference would contribute minimally to protein overexpression. These findings indicate that IRF-1 deregulation in RS485 cells occurs primarily at the transcriptional level.
Attard
Frank A
FA
Department of Pathology, The United States Military Cancer Institute, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
Contente
Sara
S
Yeh
Tze-Jou Annie
TJ
Buchhagen
Dorothy L
DL
Friedman
Robert M
RM
D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D011905:Genes, ras; D050856:Interferon Regulatory Factor-1; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D041681:NIH 3T3 Cells; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D061988:Proteasome Inhibitors; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism
D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D050856:Interferon Regulatory Factor-1; C494258:Irf1 protein, mouse; D007976:Leupeptins; D010750:Phosphoproteins; D061988:Proteasome Inhibitors; D012333:RNA, Messenger; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde