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

Abstract

It is unknown how cues from the tumor microenvironment can regulate post-transcriptional mechanisms, such as alternative splicing, that control genes that drive malignant growth. The induction of cyclooxygenase 2 (Cox-2) by integrin a3b1 in breast cancer cells can promote tumor progression. We have used RNAi to suppress a3b1 in human MDA-MB-231 breast cancer cells and then investigated changes in global gene expression. Numerous mRNAs, including Cox-2, show altered expression and/or alternative exon usage (AEU) in a3b1-deficient cells. AEU included patterns predicted to render an mRNA susceptible to degradation, such as 39-UTR variations or retention of elements that target an mRNA for nonsense-mediated decay (NMD). PCR-based analysis of a3b1-deficient cells confirmed changes in Cox-2 mRNA that might target it for NMD, including retention of an intron that harbors premature termination codons and changes within the 39-UTR. Moreover, Cox-2 mRNA has reduced stability in a3b1-deficient cells, which is partially reversed by knockdown of the essential NMD factor UPF1. Our study identifies a3b1-mediated AEU as a novel paradigm of integrin-dependent gene regulation that has potential for exploitation as a therapeutic target.

Expression of integrin α3β1 and cyclooxygenase-2 (COX2) are positively correlated in human breast cancer

“…In summary, our finding that expression of integrin α3β1 and COX2 are correlated in human IDC is likely to reflect an important physiological role for the α3β1-dependent regulation of COX2 gene expression that we described previously in cultured breast cancer cells [11,45]. Together, these findings support the concept that targeting α3β1 specifically on tumor cells may provide an alternative strategy of suppressing COX2 that circumvents adverse side effects associated with current COX2 inhibitors.…”

α3β1 Integrin Suppresses Prostate Cancer Metastasis via Regulation of the Hippo Pathway

“…Factors that influence whether α3β1 promotes or restrains tumor progression may include (i) whether the tumor secretes an α3β1 integrin ligand (38), (ii) the stage at which tumor progression is being modeled (39), (iii) the role of α3 integrin in controlling mRNA splicing (41), and (iv) the downstream signaling pathways driving malignant progression. For example, α3β1 promotes Rac activation (42), even as it limits Rho activity, and is required for Rac-driven mammary tumors (40), even as it restrains Rho-driven prostate carcinomas, as we show here.…”

Alternative RNA Structure-Coupled Gene Regulations in Tumorigenesis

“…In breast cancer, RNAi-mediated knockdown of integrin α3β1 in breast cancer cells caused changes in the splicing pattern of cancer-related genes and reduced tumorigenicity [ 70 ]. These changes might alter the 3'UTRs or generate PTCs in the affected genes, causing the mRNAs to be targeted by NMD [ 70 , 71 ]. Particularly, the altered splicing pattern of cyclooxygenase-2 (Cox-2) in α3β1-deficient cells was found to yield NMD-sensitive isoforms, which included a retained intron (and a PTC within the intron) and changed 3'UTRs [ 71 ].…”

“…These changes might alter the 3'UTRs or generate PTCs in the affected genes, causing the mRNAs to be targeted by NMD [ 70 , 71 ]. Particularly, the altered splicing pattern of cyclooxygenase-2 (Cox-2) in α3β1-deficient cells was found to yield NMD-sensitive isoforms, which included a retained intron (and a PTC within the intron) and changed 3'UTRs [ 71 ]. Of note, the induction of Cox-2 by integrin α3β1 was reported to promote tumor progression.…”

“…Of note, the induction of Cox-2 by integrin α3β1 was reported to promote tumor progression. The AS-NMD regulation of Cox-2 was thus proposed to play an important role in the tumorigenesis of breast cancer [ 71 ].…”