The tumor suppressor interferon regulatory factor 1 interferes with SP1 activation to repress the human CDK2 promoter.
Cell growth control by interferons (IFNs) involves up-regulation of the tumor suppressor interferon regulatory factor 1 (IRF1). To exert its anti-proliferative effects, this factor must ultimately control transcription of several key genes that regulate cell cycle progression. Here we show that the G1/S phase-related cyclin-dependent kinase 2 (CDK2) gene is a novel proliferation-related downstream target of IRF1. We find that IRF1, but not IRF2, IRF3, or IRF7, selectively represses CDK2 gene transcription in a dose- and time-dependent manner. We delineate the IRF1-responsive repressor element between nt -68 to -31 of the CDK2 promoter. For comparison, the tumor suppressor p53 represses CDK2 promoter activity independently of IRF1 through sequences upstream of nt -68, and the CDP/cut/Cux1 homeodomain protein represses transcription down-stream of -31. Thus, IRF1 repression represents one of three distinct mechanisms to attenuate CDK2 levels. The -68/-31 segment lacks a canonical IRF responsive element but contains a single SP1 binding site. Mutation of this element abrogates SP1-dependent enhancement of CDK2 promoter activity as expected but also abolishes IRF1-mediated repression. Forced elevation of SP1 levels increases endogenous CDK2 levels, whereas IRF1 reduces both endogenous SP1 and CDK2 protein levels. Hence, IRF1 represses CDK2 gene expression by interfering with SP1-dependent transcriptional activation. Our findings establish a causal series of events that functionally connect the anti-proliferative effects of interferons with the IRF1-dependent suppression of the CDK2 gene, which encodes a key regulator of the G1/S phase transition.
Xie
Rong-Lin
RL
Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Gupta
Sunita
S
Miele
Angela
A
Shiffman
Dov
D
Stein
Janet L
JL
Stein
Gary S
GS
van Wijnen
Andre J
AJ
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000235:genetics*; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D006801:Humans; D066298:In Vitro Techniques; D050856:Interferon Regulatory Factor-1; D051379:Mice; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011033:Podophyllin / Q000031:analogs & derivatives* / Q000378:metabolism*; D011034:Podophyllotoxin / Q000031:analogs & derivatives; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D013489:Suppression, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; C494258:Irf1 protein, mouse; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D016159:Tumor Suppressor Protein p53; C003170:mitopodozide; D011033:Podophyllin; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D011034:Podophyllotoxin