HuR contributes to cyclin E1 deregulation in MCF-7 breast cancer cells.
Many cancers overexpress cyclin E1 and its tumor-specific low molecular weight (LMW) isoforms. However, the mechanism of cyclin E1 deregulation in cancers is still not well understood. We show here that the mRNA-binding protein HuR increases cyclin E1 mRNA stability in MCF-7 breast carcinoma cells. Thus, mRNA stabilization may be a key event in the deregulation of cyclin E1 in MCF-7 cells. Compared with MCF10A immortalized breast epithelial cells, MCF-7 cells overexpress full-length cyclin E1 and its LMW isoforms and exhibit increased cyclin E1 mRNA stability. Increased mRNA stability is associated with a stable adenylation state and an increased ratio of cytoplasmic versus nuclear HuR. UV cross-link competition and UV cross-link immunoprecipitation assays verified that HuR specifically bound to the cyclin E1 3'-untranslated region. Knockdown of HuR with small interfering RNA (siRNA) in MCF-7 cells decreased cyclin E1 mRNA half-life (t(1/2)) and its protein level: a 22% decrease for the full-length isoforms and 80% decrease for the LMW isoforms. HuR siRNA also delayed G(1)-S phase transition and inhibited MCF-7 cell proliferation, which was partially recovered by overexpression of a LMW isoform of cyclin E1. Overexpression of HuR in MCF10A cells increased cyclin E1 mRNA t(1/2) and its protein level. Taken together, our data show that HuR critically contributes to cyclin E1 overexpression and its growth-promoting function, at least in part by increasing cyclin E1 mRNA stability, which provides a new mechanism of cyclin E1 deregulation in breast cancer.
Guo
Xun
X
Department of Cell Biology and Physiology, University of New Mexico Health Sciences Center, Albuquerque, NM 87131-0001, USA.
Hartley
Rebecca S
RS
D020413:3' Untranslated Regions; D000954:Antigens, Surface / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000235:genetics*; D017931:DNA Primers; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects; D006801:Humans; D015513:Oncogene Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D016601:RNA-Binding Proteins / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017384:Sequence Deletion; D014466:Ultraviolet Rays
D020413:3' Untranslated Regions; D000954:Antigens, Surface; C475820:CCNE1 protein, human; D019927:Cyclin E; D017931:DNA Primers; D051959:ELAV Proteins; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D015513:Oncogene Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D016601:RNA-Binding Proteins