MATN1

Matrilin-1 (MATN1/CMP) is a cartilage extracellular matrix protein that promotes adhesion and spreading of chondrocytes and fibroblasts by binding directly to the integrin α1 subunit of α1β1 integrin (PMID:10196235). This adhesive activity is integrin-specific: blocking antibodies against the α1 or β1 subunits abolish CMP-induced cell adhesion, whereas antibodies to other integrin subunits have little effect, and co-immunoprecipitation of radiolabeled CMP with integrin α1 confirms a direct association (PMID:10196235). Its spreading-promoting function is synergistically enhanced in the presence of native, but not denatured, type II collagen (PMID:10196235). Beyond this integrin-mediated adhesion role, no further mechanistic detail on matrilin-1 in cartilage matrix assembly has been characterized in the available corpus.

1. 1999 Medium

   Established that matrilin-1 is not merely a structural matrix component but an active adhesive ligand, identifying integrin α1β1 as its direct cell-surface receptor and pinpointing the α1 subunit as the binding partner.

   Evidence Cell adhesion/spreading assays on CMP-coated surfaces with integrin subunit-specific blocking antibodies, plus co-immunoprecipitation of radiolabeled CMP with integrin α1 and synergy assays with native type II collagen

   PMID:10196235

   Open questions at the time

   • The CMP domain mediating integrin α1 binding was not mapped
   • The molecular basis of the synergy with native type II collagen was not defined
   • Single-lab finding without independent reciprocal confirmation of the direct α1 interaction

• How matrilin-1 contributes to cartilage matrix assembly and development at the molecular level, and the structural determinants of its receptor and collagen interactions, remain unresolved.
• No structural model of the integrin α1β1 interaction surface
• No in vivo phenotype linking the adhesive activity to cartilage development
• Mechanism of collagen-dependent spreading synergy uncharacterized