Enhancing integrin ?1 inserted (I) domain affinity to ligand potentiates integrin ?1?1-mediated down-regulation of collagen synthesis.

ABSTRACT: Integrin ?1?1 binding to collagen IV, which is mediated by the ?1-inserted (I) domain, down-regulates collagen synthesis. When unligated, a salt bridge between Arg(287) and Glu(317) is thought to keep this domain in a low affinity conformation. Ligand binding opens the salt bridge leading to a high-affinity conformation. How modulating integrin ?1?1 affinity alters collagen homeostasis is unknown. To address this question, we utilized a thermolysin-derived product of the ?1?2?1 network of collagen IV (?1?2?1(IV) truncated protomer) that selectively binds integrin ?1?1. We show that an E317A substitution enhanced binding to the truncated protomer, consistent with a previous finding that this substitution eliminates the salt bridge. Surprisingly, we show that an R287A substitution did not alter binding, whereas R287E/E317R substitutions enhanced binding to the truncated protomer. NMR spectroscopy and molecular modeling suggested that eliminating the Glu(317) negative charge is sufficient to induce a conformational change toward the open state. Thus, the role played by Glu(317) is largely independent of the salt bridge. We further show that cells expressing E317A or R287E/E317R substitutions have enhanced down-regulation of collagen IV synthesis, which is mediated by the ERK/MAPK pathway. In conclusion, we have demonstrated that modulating the affinity of the extracellular ?1 I domain to collagen IV enhances outside-in signaling by potentiating ERK activation and enhancing the down-regulation of collagen synthesis.

SUBMITTER: Shi M 

PROVIDER: S-EPMC3471707 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature