Ligation of Integrin α5β1 Is Required for Internalization of Vitronectin by Integrin αvβ3

• Published in: The Journal of biological chemistry 1997-01, Vol.272 (5), p.2736
• Main Authors: Vivian Pijuan-Thompson, Candece L. Gladson
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.5.2736

Remodeling of the matrix by tumor cells is necessary for tumor invasion. We have shown previously that malignant astrocytomas, in contrast to normal astrocytes, synthesize vitronectin and express integrins α v β 3 and α v β 5 . The activity states of these two integrins are differentially controlled. Thus, we investigated the regulation of the activity of integrins α v β 3 and α v β 5 with regard to their role in vitronectin internalization in U-251MG astrocytoma cell monolayers adherent to fibronectin, collagen, or laminin in serum-free conditions. Binding of [ 125 I]vitronectin occurred in a specific, saturable manner that was partially inhibitable by monoclonal antibodies (mAbs) specific for integrins α v β 3 or α v β 5 . Specific, lysosomally-mediated degradation of [ 125 I]vitronectin was detectable at 1 h and increased over the 24-h assay period. The cell substrate affected the rate of turnover of [ 125 I]vitronectin, which was 3.0 ng/min for cells plated on fibronectin but 0.35 ng/min for cells plated on collagen. Furthermore, although mAbs specific for either integrin α v β 3 or α v β 5 inhibited degradation (30%; combined effect 70%) of [ 125 I]vitronectin by cells plated on fibronectin, only mAb anti-α v β 5 inhibited degradation (70-90%) by cells plated on collagen or laminin. To determine the requirement for integrin α 5 β 1 ligation in order for integrin α v β 3 to internalize its ligand, cells were plated on mAbs anti-integrin α 5 or anti-integrin α 3 . When plated on mAb anti-α 5 , mAbs anti-α v β 3 and anti-α v β 5 both inhibited degradation. However, when plated on mAb anti-α 3 , mAb anti-α v β 3 had no effect whereas mAb anti-α v β 5 inhibited degradation. These data indicate that a signal from integrin α 5 β 1 is necessary for integrin α v β 3 to internalize vitronectin, whereas integrin α v β 5 constitutively internalizes vitronectin.