Modulation of a conserved cathepsin b-like extracellular matrix protein impacts wing and egg formation in drosophilia melanogaster

Abstract

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 . ! ··. .· . i· , 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 interac¥ons 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' cy~teine of cathepsin is restor~d, resulted in gain-of-function defects in egg formation and larval development. We provide genetic and biochemical evidence that these ~efects 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.