Rap1 reverses transcriptional repression of TGF-beta type II receptor by a mechanism involving AP-1 in the human pancreatic cancer cell line, UK Pan-1.
The TGF-beta signaling pathway has potent anti-mitogenic effects in epithelial cells and loss of negative growth regulation is often associated with increased tumorigenicity. The human pancreatic ductal adenocarcinoma cell line, UK Pan-1, which expresses DPC4, is not highly responsive to TGF-beta due to transcriptional repression of TGF-beta type II receptor (RII). Here, we show that UK Pan-1 cells transfected with a plasmid to overexpress rap1 protein (UK/rap1) causes an increase in RII transcription and restores sensitivity to TGF-beta growth inhibition. The overexpression of rap1 was associated with diminished ras signaling as measured by ras binding domain (RBD)-binding assays. Electrophoretic mobility shift assays (EMSA) analysis revealed increased binding of nuclear proteins to a previously identified positive regulatory element (PRE1) of the RII promoter in rap1 transfected cells. Competition with an oligo containing the AP-1 consensus site was able to inhibit this binding of nuclear proteins to the PRE1 region. Further EMSA analysis using antibodies to various AP-1 components revealed that junB antibodies partially depleted the increase in binding to the PRE1 seen in UK/rap1 cells while antibodies to other AP-1 constituents such as c-jun, c-fos, and ATF-1 had no effect on binding. Consistent with this data, transient transfection of UK Pan-1 cells with junB resulted in greater RII transcription (twofold) as measured by RII-luciferase assay. Mutation of the AP-1 site inhibited junB-mediated or rap1-mediated increases in RII promoter activity. These data suggest that rap1 signaling may mediate an increase in RII transcription via increased binding of nuclear factors including junB to the PRE1 region of the RII promoter.
Fralix
Kimberly D
KD
Department of Pharmacology, University of Texas Health Science Center, San Antonio 78229, USA.
Zhao
Shujie
S
Venkatasubbarao
Kolaparthi
K
Freeman
James W
JW
D002277:Carcinoma / Q000235:genetics* / Q000378:metabolism; D002455:Cell Division / Q000235:genetics; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D005809:Genes, Regulator / Q000235:genetics*; D006801:Humans; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000235:genetics*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000235:genetics; D020827:rap1 GTP-Binding Proteins / Q000235:genetics* / Q000378:metabolism
D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D012097:Repressor Proteins; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D020928:Mitogen-Activated Protein Kinases; D000077294:Receptor, Transforming Growth Factor-beta Type II; D020827:rap1 GTP-Binding Proteins