Abrogation of Tumor Necrosis Factor-alpha converting enzyme inhibits embryonic lung morphogenesis in culture

TNF-alpha converting enzyme (TACE)-mediated cell surface protein ectodomain cleavage constitutes an important cellular regulatory mechanism during mam malian lung development. Herein, we have found that TAPI, a synthetic inhib itor of TACE, inhibits embryonic mouse lung branching morphogenesis in cult ure. To further investigate the biological significance of TACE as a sheddi ng enzyme during early lung organogenesis, we have devised an antisense oli gonucleotide to specifically block endogenous TACE gene expression at both transcriptional and translational levels in embryonic mouse lung explant cu lture. Addition of TACE antisense oligonucleotide resulted in a concentrati on-dependent reduction in lung branching morphogenesis in culture, whereas both scrambled and sense control oligonucleotides showed no adverse effects on lung growth. Furthermore, both aquaporin-5 (Aqp5) and surfactant protei n-C (SP-C) mRNA expression and protein immunoreactivity were significantly inhibited in cultured mouse lungs treated with TACE antisense oligonucleoti de, indicating defective epithelial cell differentiation in embryonic lungs with decreased TACE expression. TACE is known to be involved in the proteo lytic release of TGF-alpha, an EGF family stimuli critical for lung growth and maturation. We therefore tested the possibility that a lack of diffusab le TGF-alpha, due to TACE deficiency, contributes to the inhibitory lung mo rphogenesis in the presence of TACE antisense oligonucleotide in lung cultu re. Soluble TGF-alpha, when included in the lung culture, rescued the TACE antisense oligonucleotide-treated lungs from inhibition of both lung branch ing morphogenesis and lung epithelial cell differentiation, suggesting an i mpaired release of circulating regulators necessary for lung development in the absence of TACE gene expression. Our findings provide evidence that TA CE-mediated membrane protein shedding is indispensable for normal lung bran ching morphogenesis and cytodifferentiation, probably through regulating th e availability of positive cytokines/growth factors essential for lung orga nogenesis such as TGF-alpha.