title: Caspase-mediated cleavage of RNA-binding protein HuR regulates c-Myc protein expression after hypoxic stress.
abstract: Altered expression of RNA-binding proteins modulates gene expression in association with mRNAs encoding many proto-oncogenes, cytokines, chemokines, and proinflammatory factors. Hu antigen R (HuR), a ubiquitously expressed protein, controls a range of cellular functions such as tumor progression, apoptosis, invasion, and metastasis by stabilizing the AU-rich element located at the 3'-untranslated region (UTR) of target mRNAs. Although significant progress has been made in understanding HuR regulation in gene expression, little is known about how HuR undergoes post-translational modifications and recruits target mRNAs during hypoxic stress. Here, we report that during CoCl(2)-induced hypoxic stress, HuR is significantly overexpressed and undergoes caspase-dependent cleavage in head and neck squamous cell carcinoma cells. Unexpectedly, the HuR-cleavage product 1 (HuR-CP1) was found to strongly associate with the 3'-UTR of c-myc mRNA and block mRNA translation. The binding efficiency of HuR to the 3'-UTR of c-myc mRNA was confirmed using ribonucleoprotein immunoprecipitation and site-directed mutagenesis at the AU-rich element sequences of the c-myc mRNA. Overexpression of a non-cleavable isoform, HuR-D226A, revealed a potent dominant-negative effect, repressing cleavage of endogenous HuR and promoting cell viability. Surprisingly, under hypoxia, siRNA knockdown of HuR elevated c-Myc protein expression. These findings suggest an important role for HuR in hypoxia, and we may have revealed a novel post-transcriptional mechanism that controls c-Myc expression in oral cancer progression.
authors.affiliation: Department of Craniofacial Biology, College of Dental Medicine, Medical University of SouthCarolina, Charleston, South Carolina 29425, USA.
authors.forename: Sudha
authors.initials: S
authors.lastname: Talwar
authors.forename: Junfei
authors.initials: J
authors.lastname: Jin
authors.forename: Brittany
authors.initials: B
authors.lastname: Carroll
authors.forename: Angen
authors.initials: A
authors.lastname: Liu
authors.forename: Marion Boyd
authors.initials: MB
authors.lastname: Gillespie
authors.forename: Viswanathan
authors.initials: V
authors.lastname: Palanisamy
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics; D002294:Carcinoma, Squamous Cell / Q000235:genetics / Q000378:metabolism*; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D003035:Cobalt / Q000494:pharmacology; D051959:ELAV Proteins / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D009062:Mouth Neoplasms / Q000235:genetics / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis* / Q000235:genetics; D013312:Stress, Physiological
chemical_list: D020413:3' Untranslated Regions; D051959:ELAV Proteins; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D003035:Cobalt; C018021:cobaltous chloride