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

Abstract

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 where 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 over-expressed 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 crosstalk 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.

Hypoxia-induced Changes to Integrin α 3 Glycosylation Facilitate Invasion in Epidermoid Carcinoma Cell Line A431

“…5B and 5C). It has been reported that integrin ␣3␤1 promotes radiation-induced migration of meningioma cells and that suppression of integrin ␣3␤1 inhibits tumorigenesis and invasion in breast cancer cells (66). Our transwell assay on the ITGA3 knockdown cells also supported the same conclusion.…”

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

“…Preclinical studies have shown that a3b1 promotes malignant behavior of breast cancer cells in vivo and in vitro (Cagnet et al, 2013;Mitchell et al, 2010;Morini et al, 2000;Scales et al, 2013;Sugiura and Berditchevski, 1999;Wang et al, 2004), as well as skin tumorigenesis in vivo (Sachs et al, 2012), implicating this integrin as a potential therapeutic target to inhibit cancer progression and metastasis (Subbaram and DiPersio, 2011). Laminin-332, a major ECM ligand for a3b1, is often expressed highly in breast cancer cells, where it enhances motility (Carpenter et al, 2009;Carpenter et al, 2008).…”

“…Laminin-332, a major ECM ligand for a3b1, is often expressed highly in breast cancer cells, where it enhances motility (Carpenter et al, 2009;Carpenter et al, 2008). At least some functions of a3b1 in transformed or immortalized cells are attributable to the ability of a3b1 to regulate genes that stimulate invasive growth and/or angiogenesis, including matrix metalloproteinase-9 (MMP-9) (Iyer et al, 2005;Morini et al, 2000) and cyclooxygenase (Cox-2, also known as prostaglandin G/H synthase 2 in human) (Mitchell et al, 2010). In immortalized keratinocytes, a3b1-dependent-induction of MMP-9 occurs through a post-transcriptional mechanism of enhanced mRNA stability (Iyer et al, 2005).…”

“…We previously showed that stable, shRNA-mediated suppression of a3b1 in MDA-MB-231 breast cancer cells reduced expression of the Cox-2 gene and abrogated tumor growth in an orthotopic model (Mitchell et al, 2010). To determine whether acute suppression of a3b1 similarly reduces Cox-2 expression, and whether this regulation extends to other breast cancer lines, we transfected MDA-MB-231 cells or MCF7 cells each with two different siRNAs that target the a3 integrin subunit (hereafter referred to as a3).…”

COX-2 expression correlation with invasion in human breast carcinomas and in cell line MDA-MB-231 in vitro

“…COX-2 is an inducible enzyme that interferes with tumor development and angiogenesis, related to the inhibition of apoptosis through inhibition of the proapoptotic Bax protein and overexpression of the antiapoptotic bcl-2 protein. COX-2 catalyzes the conversion of arachidonic acid to PGE2 and enhances the metastatic phenotype of both breast cancer cells in vitro and breast tumors (Mitchell et al, 2010;Miglietta et al, 2010). PGE2, the catalytic product of COX-2, may promote tumor development and angiogenesis (Boland et al, 2004;Miglietta et al, 2010;Yu et al, 2014).…”