Urokinase Receptors Promote β1 Integrin Function through Interactions with Integrin α3β1

Abstract

The urokinase receptor (uPAR) is linked to cellular migration through its capacity to promote pericellular proteolysis, regulate integrin function, and mediate cell signaling in response to urokinase (uPA) binding. The mechanisms for these activities remain incompletely defined, although uPAR was recently identified as a cis-acting ligand for the ␤2 integrin CD11b/CD18 (Mac-1). Here we show that a major ␤1 integrin partner for uPAR/uPA signaling is ␣3. In uPAR-transfected 293 cells uPAR complexed (Ͼ90%) with ␣3␤1 and antibodies to ␣3 blocked uPAR-dependent vitronectin (Vn) adhesion. Soluble uPAR bound to recombinant ␣3␤1 in a uPA-dependent manner (K d Ͻ 20 nM) and binding was blocked by a 17-mer ␣3␤1 integrin peptide (␣325) homologous to the CD11b uPARbinding site. uPAR colocalized with ␣3␤1 in MDA-MB-231 cells and uPA (1 nM) enhanced spreading and focal adhesion kinase phosphorylation on fibronectin (Fn) or collagen type I (Col) in a pertussis toxin-and ␣325-sensitive manner. A critical role of ␣3␤1 in uPA signaling was verified by studies of epithelial cells from ␣3-deficient mice. Thus, uPAR preferentially complexes with ␣3␤1, promoting direct (Vn) and indirect (Fn, Col) pathways of cell adhesion, the latter a heterotrimeric G proteindependent mechanism of signaling between ␣3␤1 and other ␤1 integrins.

Calcitonin stimulates the secretion of urokinase‐type plasminogen activator from prostate cancer cells: Its possible implications on tumor cell invasion

“…43 uPA has been shown to break down various components of extracellular matrix, including laminin, fibronectin and collagen through the generation of plasmin. 16 In general, tumor cells of several human malignancies express detectable cell surface-associated uPA and plasmin activity, and this positively correlates with their invasiveness.…”

A direct link between expression of urokinase plasminogen activator receptor, growth rate and oncogenic transformation in mouse embryonic fibroblasts

“…Available data in cultured cancer cells, however, indicate that uPAR overexpression activates cell proliferation by interacting with integrins and with growth factor receptor tyrosine kinases like the EGF and the PDGF receptors (Liu et al, 2002;Kiyan et al, 2005). However, peptide a325 that dissociates uPAR-a3b1 and -a5b1 complexes (Wei et al, 2001;Mazzieri et al, 2006) had no effect on wt MEFs growth rate or ERK activation (data not shown). It is known that overexpression of uPAR in Hep3 cells, for example, modifies the response of the EGF-R to EGF, so that EGF-R was activated in the absence of EGF (Liu et al, 2002).…”

Urokinase-type plasminogen activator induces proliferation in breast cancer cells

“…Previously, we demonstrated this integrin-uPA interaction in tumor-associated macrophages of breast cancer (12). Furthermore, it was demonstrated that integrins (·3ß1) are associated with uPAR in MDA-MB-231 breast cancer cells (13). Since uPAR lacks transmembrane and intracytoplasmic domain for uPA-induced signal tranduction, uPAR-integrin collaboration is essential.…”

“…Whereas, for cell counting, cells were trypsinized and counted using a hemocytometer. It was demonstrated by Wei et al that ·3ß1 integrins are associated with uPAR in MDA-MB-231 breast cancer cells (13). uPAR-dependent functions are blocked by antibodies to ·3 (P1B5).…”