Integrin α3β1 controls mRNA splicing that determines cyclooxygenase-2 (Cox-2) mRNA stability in breast cancer cells

Abstract

Recent studies have shown that alterations in mRNA content, achieved through post-transcriptional mechanisms such as alternative splicing or polyadenylation, are critical for regulation of cancer-promoting genes by determining transcript susceptibility to mRNA degradation pathways. However, it remains unclear how cues from the tumor microenvironment trigger this regulation to control genes that drive malignant growth. Expression of integrin α3β1 in breast cancer cells promotes tumor growth and invasion, in part through induction of cyclooxygenase-2 (Cox-2). In the current study, we used RNAi to suppress α3β1 in human MDA-MB-231 breast cancer cells, then utilized exon microarrays to compare global gene expression between control and α3β1-deficient cells. This analysis identified numerous mRNAs, including Cox-2, that show altered expression and/or alternate exon usage (AEU) in α3β1-deficient cells. AEU included patterns predicted to render a mRNA susceptible to degradation, such as 3′-UTR variations or retention of elements that target it for nonsense-mediated decay (NMD). PCR-based analysis of α3β1-deficient cells confirmed changes in Cox-2 mRNA that may target it for NMD, including retention of an intron that harbors premature termination codons and changes within the 3′-UTR. Consistently, Cox-2 mRNA stability was reduced in α3β1-deficient cells, and siRNA-mediated knockdown of UPF1 (an essential NMD factor) in these cells led to Cox-2 mRNA accumulation. Our study identifies α3β1-mediated AEU as a novel paradigm of integrin-dependent gene regulation that may be exploitable as a therapeutic target to inhibit breast cancer.