Identification and characterization of a novel extracellular matrix protein nephronectin that is associated with integrin α8β1 in the embryonic kidney

Abstract

The epithelial–mesenchymal interactions required for kidney organogenesis are disrupted in mice lacking the integrin α8β1. None of this integrin's known ligands, however, appears to account for this phenotype. To identify a more relevant ligand, a soluble integrin α8β1 heterodimer fused to alkaline phosphatase (AP) has been used to probe blots and cDNA libraries. In newborn mouse kidney extracts, α8β1-AP detects a novel ligand of 70–90 kD. This protein, named nephronectin, is an extracellular matrix protein with five EGF-like repeats, a mucin region containing a RGD sequence, and a COOH-terminal MAM domain. Integrin α8β1 and several additional RGD-binding integrins bind nephronectin. Nephronectin mRNA is expressed in the ureteric bud epithelium, whereas α8β1 is expressed in the metanephric mesenchyme. Nephronectin is localized in the extracellular matrix in the same distribution as the ligand detected by α8β1-AP and forms a complex with α8β1 in vivo. Thus, these results strongly suggest that nephronectin is a relevant ligand mediating α8β1 function in the kidney. Nephronectin is expressed at numerous sites outside the kidney, so it may also have wider roles in development. The approaches used here should be generally useful for characterizing the interactions of novel extracellular matrix proteins identified through genomic sequencing projects.

The interaction of versican with its binding partners

“…Most integrins recognize several ECM proteins. For example, integrin β1 pairs with various α subunits to bind a variety of ECM molecules, such as fibronectin, laminins, collagens, and vitronectin, osteopontin [89], nephronectin [90] and tenascin [91].…”

Integrins in regulation of tissue development and function

“…Some can be ruled out as they are undetectable in kidney, while mice deficient in osteopontin, an α8β1 ligand which is expressed in the kidney, show no apparent abnormal kidney phenotype. Nephronectin is another ligand of α8β1 that is expressed in kidney [90], but it remains to be established which role nephronectin plays in the development and function of the kidney.…”

Age-Related Changes in Cochlear Gene Expression In Normal and Shaker 2 Mice

“…Nephronectin, a component of the basement membrane of several embryonic tissues (Brandenberger et al 2001), interacts with integrin a8b1 in vitro and in embryonic kidney in vivo (Brandenberger et al 2001;Morimura et al 2001). Mice carrying targeted disruption of Itga8 for integrin a8b1 have stereocilia defects, suggesting that integrin a8b1 plays a role in regulating hair-cell differentiation and stereocilia maturation (Littlewood Evans and Muller 2000).…”

“…Mice carrying targeted disruption of Itga8 for integrin a8b1 have stereocilia defects, suggesting that integrin a8b1 plays a role in regulating hair-cell differentiation and stereocilia maturation (Littlewood Evans and Muller 2000). Early in development (E14.5), nephronectin is found in the basal lamina of the otocyst, but later mainly on the apical epithelial surface outside the developing sensory region (Brandenberger et al 2001). Integrin a8b1 is found on the apical surface of auditory and vestibular hair cells from E16 to P0 (Littlewood Evans and Muller 2000).…”