title: Repression of caspase-3 and RNA-binding protein HuR cleavage by cyclooxygenase-2 promotes drug resistance in oral squamous cell carcinoma.
abstract: A well-studied RNA-binding protein Hu Antigen-R (HuR), controls post-transcriptional gene regulation and undergoes stress-activated caspase-3 dependent cleavage in cancer cells. The cleavage products of HuR are known to promote cell death; however, the underlying molecular mechanisms facilitating caspase-3 activation and HuR cleavage remains unknown. Here, we show that HuR cleavage associated with active caspase-3 in oral cancer cells treated with ionizing radiation and chemotherapeutic drug, paclitaxel. We determined that oral cancer cells overexpressing cyclooxygenase-2 (COX-2) limited the cleavage of caspase-3 and HuR, which reduced the rate of cell death in paclitaxel resistant oral cancer cells. Specific inhibition of COX-2 by celecoxib, promoted apoptosis through activation of caspase-3 and cleavage of HuR in paclitaxel-resistant oral cancer cells, both in vitro and in vivo. In addition, oral cancer cells overexpressing cellular HuR increased the half-life of COX-2 mRNA, promoted COX-2 protein expression and exhibited enhanced tumor growth in vivo in comparison with cells expressing a cleavable form of HuR. Finally, our ribonucleoprotein immunoprecipitation and sequencing (RIP-seq) analyses of HuR in oral cancer cells treated with ionizing radiation (IR), determined that HuR cleavage product-1 (HuR-CP1) bound and promoted the expression of mRNAs encoding proteins involved in apoptosis. Our results indicated that, cellular non-cleavable HuR controls COX-2 mRNA expression and enzymatic activity. In addition, overexpressed COX-2 protein repressed the cleavage of caspase-3 and HuR to promote drug resistance and tumor growth. Altogether, our observations support the use of the COX-2 inhibitor celecoxib, in combination with paclitaxel, for the management of paclitaxel resistant oral cancer cells.
authors.affiliation: Department of Oral Health Sciences and Center for Oral Health Research, College of Dental Medicine, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: H
authors.initials: H
authors.lastname: Janakiraman
authors.affiliation: Department of Oral Health Sciences and Center for Oral Health Research, College of Dental Medicine, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: House
authors.affiliation: Department of Oral Health Sciences and Center for Oral Health Research, College of Dental Medicine, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: S
authors.initials: S
authors.lastname: Talwar
authors.affiliation: Center for Genomics Medicine, Medical University of South Carolina, Charleston, SC, USA.|Department of Pathology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Courtney
authors.affiliation: Center for Genomics Medicine, Medical University of South Carolina, Charleston, SC, USA.|Library Science and Informatics, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Hazard
authors.affiliation: Center for Genomics Medicine, Medical University of South Carolina, Charleston, SC, USA.|Departments of Medicine and Public Health, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: G
authors.initials: G
authors.lastname: Hardiman
authors.affiliation: Department of Surgery, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: S
authors.initials: S
authors.lastname: Mehrotra
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: P H
authors.initials: PH
authors.lastname: Howe
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: V
authors.initials: V
authors.lastname: Gangaraju
authors.affiliation: Department of Oral Health Sciences and Center for Oral Health Research, College of Dental Medicine, Medical University of South Carolina, Charleston, SC, USA.|Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: V
authors.initials: V
authors.lastname: Palanisamy
mesh_terms: D002294:Carcinoma, Squamous Cell / Q000235:genetics* / Q000473:pathology; D053148:Caspase 3 / Q000378:metabolism*; D051546:Cyclooxygenase 2 / Q000235:genetics*; D006801:Humans; D009062:Mouth Neoplasms / Q000235:genetics* / Q000473:pathology; D016601:RNA-Binding Proteins / Q000378:metabolism*
chemical_list: D016601:RNA-Binding Proteins; D051546:Cyclooxygenase 2; D053148:Caspase 3