Induction of p21WAF1/CIP1 and cyclin D1 expression by the Src oncoprotein in mouse fibroblasts: role of activated STAT3 signaling.
While the activated viral Src oncoprotein, v-Src, induces uncontrolled cell growth, the mechanisms underlying cell cycle deregulation by v-Src have not been fully defined. Previous studies demonstrated that v-Src induces constitutively active STAT3 signaling that is required for cell transformation and recent data have implicated STAT3 in the transcriptional control of critical cell cycle regulators. Here we show in mouse fibroblasts stably transformed by v-Src that mRNA and protein levels of p21 (WAF1/CIP1), cyclin D1, and cyclin E are elevated. Using reporter constructs in transient-transfection assays, the cyclin D1 and p21 promoters were both found to be transcriptionaly induced by v-Src in a STAT3-dependent manner. The kinase activities of cyclin D/CDK4, 6 and cyclin E/CDK2 complexes were only slightly elevated, consistent with the findings that coordinate increases in p21, cyclin D1 and cyclin E resulted in an increase in cyclin/CDK/p21 complexes. Similar results were obtained in NIH3T3 and BALB/c 3T3 cells stably transformed by v-Src, indicating that these regulatory events associated with STAT3 signaling represent common mechanisms independent of cell line or clonal variation. These findings suggest that STAT3 has an essential role in the regulation of critical cell cycle components in v-Src transformed mouse fibroblasts.
Sinibaldi
D
D
Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, University of South Florida College of Medicine, Tampa 33612, USA.
Wharton
W
W
Turkson
J
J
Bowman
T
T
Pledger
W J
WJ
Jove
R
R
D016475:3T3 Cells / Q000378:metabolism / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D002453:Cell Cycle / Q000502:physiology; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D019938:Cyclin D1 / Q000096:biosynthesis* / Q000235:genetics; D019927:Cyclin E / Q000096:biosynthesis / Q000235:genetics; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D015688:Oncogene Protein pp60(v-src) / Q000502:physiology*; D011233:Precipitin Tests; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D050796:STAT3 Transcription Factor; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D015854:Up-Regulation
C493957:Cdkn1a protein, mouse; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D019938:Cyclin D1; D015688:Oncogene Protein pp60(v-src)