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 mammalian lung development. Herein, we have found that TAPI, a synthetic inhibitor of TACE, inhibits embryonic mouse lung branching morphogenesis in culture. To further investigate the biological significance of TACE as a shedding enzyme during early lung organogenesis, we have devised an antisense oligonucleotide to specifically block endogenous TACE gene expression at both transcriptional and translational levels in embryonic mouse lung explant culture. Addition of TACE antisense oligonucleotide resulted in a concentration-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 protein-C (SP-C) mRNA expression and protein immunoreactivity were significantly inhibited in cultured mouse lungs treated with TACE antisense oligonucleotide, indicating defective epithelial cell differentiation in embryonic lungs with decreased TACE expression. TACE is known to be involved in the proteolytic release of TGF-alpha, an EGF family stimuli critical for lung growth and maturation. We therefore tested the possibility that a lack of diffusable TGF-alpha, due to TACE deficiency, contributes to the inhibitory lung morphogenesis in the presence of TACE antisense oligonucleotide in lung culture. Soluble TGF-alpha, when included in the lung culture, rescued the TACE antisense oligonucleotide-treated lungs from inhibition of both lung branching morphogenesis and lung epithelial cell differentiation, suggesting an impaired release of circulating regulators necessary for lung development in the absence of TACE gene expression. Our findings provide evidence that TACE-mediated membrane protein shedding is indispensable for normal lung branching morphogenesis and cytodifferentiation, probably through regulating the availability of positive cytokines/growth factors essential for lung organogenesis such as TGF-alpha.