• Modulation of a Conserved Cathepsin B-Like Extracellular Matrix Protein Impacts Wing and Egg Formation in Drosphila Melanogaster

      Dinkins, Michael B; Department of Cellular Biology and Anatomy (2011-03)
      Conserved in Bilaterian species, the tubulointerstitial nephritis antigen (TIN-ag) family of cathepsin B-like extracellular matrix proteins has been proposed to have roles in cell adhesion and regulation of basement membrane assembly based on in vitro studies of mammalian family members. Here we examined the single Drosophila ortholog, CG3074, and found conservation of its basement membrane localization as well as a role in cell adhesion. RNAi knockdown resulted in wing blistering and held-out wings following eclosion, consistent with defects in adhesion of wing epithelia and tendon cells to the underlying extracellular matrix, but no defects were detected during pupal development. We were unable to demonstrate a genetic or physical interaction with laminin and CG3074 but did detect genetic interactions with integrins and dystroglycan in the wing. A serine substitutes for cysteine in all TIN-ag family members at the 'active site' of the cathepsin B-like domain and is predicted to render the protein inactive as a protease. Overexpression of the mutant CG3074 S213C, in which the 'catalytic' cysteine of cathepsin is restored, resulted in gain-of-function defects in egg formation and larval development. We provide genetic and biochemical evidence that these defects arise from a neomorphic activity of the S213C protein that supports a role of this highly conserved domain in wildtype CG3074 function. These studies broaden our understanding of TINag family function and identify tissue and pathway models for future studies.