Muscle cell integrins in vitro and in vivo : Identification and characterisation of a novel integrin, α11β1

Abstract: Integrins are heterodimeric receptors composed of non-covalently associated αand β subunits which have distinct functions on different cell types. α7β1integrin is an important laminin receptor in skeletal muscle. The mRNA andprotein expression patterns of α7A and α7B splice variants during mousedevelopment were studied. Distinct patterns of expression of the splice variantswere seen, including sites in non-muscle tissues such as a subset of blood vessels,and sites in central and peripheral nervous systems.A novel β1-associated I-domain containing integrin α-chain wasidentified on cultured human foetal myogenic cells, and found to be upregulatedduring in vitro differentiation. Chromosome mapping localised ITGA11 tohuman chromosome 15q23. Three features distinguished the α11 subunit frompreviously known integrin α-chains: 1) the presence of a unique domain in theextracellular membrane proximal portion of the polypeptide, 2) the motifGFFRS instead of the conserved GFFKR, at the membrane-cytoplasm interface,and 3) a sequence of the cytoplasmic domain containing a putative cleavage sitefor proteolytic enzymes.The expression of α11 mRNA and protein at different embryonic andfoetal developmental stages was studied. Contrary to the expectations, noprominent expression of either α11 mRNA or protein was seen in muscle tissues. α11 subunit mRNA and protein were instead localised to regions adjacent to collagen type II-containing chondrogenic tissues, intervertebral discs, andkeratocytes in cornea. Based on the distribution pattern a role for integrin α11β1in the organisation of interstitial collagens was proposed.