Y-box-binding protein 1 confers EGF independence to human mammary epithelial cells.
The epidermal growth factor receptor (EGFR) is linked to poor outcome in breast cancer, and resistance to hormonal therapy is often accompanied by activation of growth factor receptors. To investigate the mechanism(s) by which EGFR becomes activated in breast cancer, we screened a cDNA expression library for genes that mediate EGF-independent proliferation of human mammary epithelial cells (HMECs). We isolated the NSEP1 cDNA encoding Y-box-binding protein 1 (YB-1), a multifunctional transcriptional and translational regulator. This cDNA conferred growth factor independence to HMECs. YB-1-transduced cells overexpressed EGFR, but ErbB-2 (Her-2/neu) levels were unchanged. Moreover, EGFR was constitutively phosphorylated in the absence of exogenous ligand. In these cells, an EGFR-blocking antibody failed to inhibit proliferation, conditioned medium activity could not be detected, and the synthesis of EGFR ligands was reduced compared to parental cells. This suggests that EGFR is activated in a ligand-independent fashion. However, cell growth could be blocked with an ErbB kinase inhibitor, indicating that EGFR signaling plays a major role in YB-1-induced growth factor independence. Taken together, our results demonstrate that YB-1 overexpression can induce EGF independence in HMECs via activation of the EGFR pathway. This could represent one of the mechanisms by which YB-1 contributes to breast tumor aggressiveness.
Berquin
Isabelle M
IM
Department of Pathology, Wake Forest University, Winston-Salem, NC 27157, USA. iberquin@wfubmc.edu
Pang
Bing
B
Dziubinski
Michele L
ML
Scott
Latanya M
LM
Chen
Yong Q
YQ
Nolan
Garry P
GP
Ethier
Stephen P
SP
D000483:Alleles; D015152:Blotting, Northern; D001940:Breast / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism*; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D015723:Gene Library; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008024:Ligands; D008856:Microscopy, Fluorescence; D051839:NFI Transcription Factors; D009361:Neoplasm Invasiveness; D010766:Phosphorylation; D014176:Protein Biosynthesis; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D051840:Y-Box-Binding Protein 1
D022762:CCAAT-Enhancer-Binding Proteins; D018076:DNA, Complementary; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D008024:Ligands; D051839:NFI Transcription Factors; D018719:Erb-b2 Receptor Tyrosine Kinases; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1