αv Integrin, p38 Mitogen-activated Protein Kinase, and Urokinase Plasminogen Activator Are Functionally Linked in Invasive Breast Cancer Cells

Abstract

We reported previously that endogenous p38 MAPK activity is elevated in invasive breast cancer cells and that constitutive p38 MAPK activity is important for overproduction of uPA in these cells (Huang, S., New, L., Pan, Z., Han, J., and Nemerow, G. R. (2000) J. Biol. Chem. 275, 12266 -12272). However, it is unclear how elevated endogenous p38 MAPK activity is maintained in invasive breast cancer cells. In the present study, we found that blocking ␣ v integrin functionality with a functionblocking monoclonal antibody or down-regulating ␣ v integrin expression with ␣ v -specific antisense oligonucleotides significantly decreased the levels of active p38 MAPK and inhibited cell-associated uPA expression in invasive breast cancer MDA-MB-231 cells. These results suggest a function link between ␣ v integrin, p38 MAPK activity, and uPA expression in invasive tumor cells. We also found that vitronectin/␣ v integrin ligation specifically induced p38 MAPK activation and uPA up-regulation in invasive MDA-MB-231 cells but not in non-invasive MCF7 cells. Finally, using a panel of melanoma cells, we demonstrated that the cytoplasmic tail of ␣ v integrin subunit is required for ␣ v integrin ligation-induced p38 MAPK activation.The degradation of extracellular matrix and basement by tumor-associated proteases is an essential process required for cancer cell invasion and metastasis (1, 2). Urokinase plasminogen activator (uPA) 1 is of particular importance because uPA, through interaction with the uPA receptor (uPAR), facilitates the conversion of plasminogen into plasmin and the activation of metalloproteinases (3, 4). These proteases then allow cancer cells to degrade the surrounding matrix proteins and migrate to the distant sites (5). The overexpression of uPA is detected in various malignancies including breast, prostate, and colon cancers (6 -8). Recent studies (9 -13) have shown further that a high level of uPA in tumors is associated with a rapid disease progression and poor prognosis in breast cancers. In addition, studies performed in experimental models both in vitro and in vivo demonstrate that the levels of uPA are closely associated with the degree of tumor cell invasion (14 -18). Blocking uPA expression or disruption of uPA binding to uPAR has been found to inhibit significantly tumor cell invasion and metastasis in various tumor models (19 -22). From these facts, it is apparent that uPA plays a key role in tumor progression and metastasis.Integrins are heterodimers composed of noncovalently associated ␣ and ␤ subunits. There are at least 14 ␣ and 8 ␤ subunits, forming at least 21 different integrins, which are the major receptors for extracellular matrix proteins (23). The ␣ v integrins are a major subfamily with restricted tissue/cell distribution (23). They have classical integrin functions such as mediating cell attachment and spreading (24, 25), facilitating cell migration (26), and ligand-receptor internalization (27, 28). They also play an important role in tumor progression and metastasis by mediating a...

Urokinase-type plasminogen activator induces proliferation in breast cancer cells

“…It was reported by Sitrin et al that integrins and uPAR are associated via carbohydrate-lectin interaction and that this physical association is necessary for collaboration (23). Recent studies have shown that integrins can activate the p38 MAPK pathway and that · v integrin, p38 MAPK and uPA are functionally linked in breast cancer cells (14). These earlier observations prompted us to investigate whether the p38 MAPK pathway is important for breast cancer cell proliferation.…”

“…Since uPAR lacks transmembrane and intracytoplasmic domain for uPA-induced signal tranduction, uPAR-integrin collaboration is essential. It was demonstrated that endogenous p38 mitogen-associated protein kinase (MAPK) activity is elevated in cultured breast cancer cells and that increased p38 MAPK activity is essential for breast cancer invasiveness by stabilizing uPA mRNA (14,15). Signal transduction via integrin may induce the MAPK pathway, since recent studies have shown that p38 MAPK modulates the proliferation of cancer cells.…”

The possible role of matrix metalloproteinase (MMP)-2 and MMP-9 in cancer, e.g. acute leukemia

“…An integrin receptor strongly involved in angiogenesis and tumor growth is ␣ v ␤ 3 -integrin [67][68][69]. This integrin can bind vitronectin and fibronectin and various other proteins with an arginine-glycine-aspartic acid (RGD) (Arg-Gly-Asp) sequence, like fibrinogen, von Willebrand factor and denatured collagen [62,66].…”

“…This integrin can bind vitronectin and fibronectin and various other proteins with an arginine-glycine-aspartic acid (RGD) (Arg-Gly-Asp) sequence, like fibrinogen, von Willebrand factor and denatured collagen [62,66]. Different reports have correlated expression of integrins with more invasive phenotypes of tumor cells and activation of MT1-MMP and MMP-2 [67,[69][70][71]. An explanation for the activation of MMP-2 is its capacity to bind ␣ v ␤ 3 -integrin through its fibronectin like repeats.…”

No association of breast cancer risk with integrin beta3 (ITGB3) Leu33Pro genotype

“…Although two later case -control studies did not confirm an increased risk of invasive breast cancer among Leu33Pro homozygotes (Ayala et al, 2003;Jin et al, 2004), certain considerations nevertheless favour the possibility that the ITGB3 Leu33Pro polymorphism may influence risk of invasive breast cancer. First, beta 3 integrins are ectopically expressed on breast carcinoma cells where they enhance invasive and metastasiogenic properties of these cells (Murthy et al, 1996;Wewer et al, 1997;Chen et al, 2001Chen et al, , 2004Rolli et al, 2003). Second, the Pro33 vs Leu33 allele enhances integrin-mediated activation of MAPK pathways (Vijayan et al, 2003), crucial for the malignant potential of cancer cells (Johnson and Lapadat, 2002).…”