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Supplementary Figure Legends 1-5, Table Legend from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Figure 2 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Figure 3 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Table 1 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Figure 5 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Figure 1 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Supplementary Figure 4 from Suppression of Integrin α3β1 in Breast Cancer Cells Reduces Cyclooxygenase-2 Gene Expression and Inhibits Tumorigenesis, Invasion, and Cross-Talk to Endothelial Cells

Integrin receptors for cell adhesion to extracellular matrix have important roles in promoting tumor growth and progression. Integrin α3β1 is highly expressed in breast cancer cells in which it is thought to promote invasion and metastasis; however, its roles in regulating malignant tumor cell behavior remain unclear. In the current study, we used short-hairpin RNA (shRNA) to show that suppression of α3β1 in a human breast cancer cell line, MDA-MB-231, leads to decreased tumorigenicity, reduced invasiveness, and decreased production of factors that stimulate endothelial cell migration. Real-time PCR revealed that suppression of α3β1 caused a dramatic reduction in expression of the cyclooxygenase-2 (COX-2) gene, which is frequently overexpressed in breast cancers and has been exploited as a therapeutic target. Decreased COX-2 was accompanied by reduced prostaglandin E2 (PGE2), a major prostanoid produced downstream of COX-2 and an important effector of COX-2 signaling. shRNA-mediated suppression of COX-2 showed that it has a role in tumor cell invasion and cross-talk to endothelial cells. Furthermore, treatment with PGE2 restored these functions in α3β1-deficient MDA-MB-231 cells. These findings identify a role for α3β1 in regulating two properties of tumor cells that facilitate cancer progression: invasiveness and ability to stimulate endothelial cells. They also reveal a novel role for COX-2 as a downstream effector of α3β1 in tumor cells, thereby identifying α3β1 as a potential therapeutic target to inhibit breast cancer. Cancer Res; 70(15); 6359–67. ©2010 AACR.

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.

Integrin receptors for cell adhesion to extracellular matrix have important roles in promoting tumor growth and progression. Integrin α3β1 is highly expressed in breast cancer cells in which it is thought to promote invasion and metastasis; however, its roles in regulating malignant tumor cell behavior remain unclear. In the current study, we used short-hairpin RNA (shRNA) to show that suppression of α3β1 in a human breast cancer cell line, MDA-MB-231, leads to decreased tumorigenicity, reduced invasiveness, and decreased production of factors that stimulate endothelial cell migration. Real-time PCR revealed that suppression of α3β1 caused a dramatic reduction in expression of the cyclooxygenase-2 (COX-2) gene, which is frequently overexpressed in breast cancers and has been exploited as a therapeutic target. Decreased COX-2 was accompanied by reduced prostaglandin E2 (PGE2), a major prostanoid produced downstream of COX-2 and an important effector of COX-2 signaling. shRNA-mediated suppression of COX-2 showed that it has a role in tumor cell invasion and cross-talk to endothelial cells. Furthermore, treatment with PGE2 restored these functions in α3β1-deficient MDA-MB-231 cells. These findings identify a role for α3β1 in regulating two properties of tumor cells that facilitate cancer progression: invasiveness and ability to stimulate endothelial cells. They also reveal a novel role for COX-2 as a downstream effector of α3β1 in tumor cells, thereby identifying α3β1 as a potential therapeutic target to inhibit breast cancer. Cancer Res; 70(15); 6359–67. ©2010 AACR.