A novel developmentally regulated gene in lung mesenchyme: homology to a tumor-derived trypsin inhibitor

Abstract

We used differential display-PCR (DD-PCR) to identify glucocorticoid-inducible genes that regulate lung development in late gestation. DD-PCR, a method to screen for differentially expressed genes, is based on a comparison of mRNAs isolated from a subset of two or more cell populations by analysis of RT-PCR products on DNA-sequencing gels. We isolated cDNA probes representing mRNAs expressed in primary cultures of rat lung fibroblasts, but not in epithelial cells, on fetal day 20. A day 20 glucocorticoid-treated fibroblast cDNA library was screened with a single probe to isolate the 3.1-kb cDNA late-gestation lung 1( LGL1; GenBank accession no. AF109674 ) encoding a deduced polypeptide of 188 amino acids. Northern analysis confirmed that LGL1is expressed in human, rat, and mouse fetal lungs, induced by glucocorticoid, developmentally regulated in fibroblasts but not detectable in epithelium. In situ hybridization confirmed LGL1 expression in the mesenchyme, but not in the epithelium, of fetal rat lung, kidney, and gut. The predicted LGL1 gene product (lgl1) showed 81% homology to P25TI, a polypeptide trypsin inhibitor recently identified in human glioblastoma and neuroblastoma cells but not detected in normal human tissues. Both lgl1 and P25TI belong to the CRISP family of cysteine-rich extracellular proteins. Trypsin is produced by both normal bronchial epithelial and lung adenocarcinoma cells. Although additional studies will be necessary to clearly establish a functional role for lgl1, we propose that lgl1 has a role in normal lung development that is likely to be via regulation of extracellular matrix degradation.

Lgl1 Is Suppressed in Oxygen Toxicity Animal Models of Bronchopulmonary Dysplasia and Normalizes During Recovery in Air

“…LGL1 was also detected in the fetal heart, intestine, kidney, liver, and spleen (7). We demonstrated antisense LGL1 inhibition of airway branching in rat lung explant culture (9), suggesting that lgl1 stimulates airway branching morphogenesis.…”

“…We cloned LGL1, a GC and developmentally regulated gene encoding a secreted glycoprotein (lgl1) that is, in the lung, expressed predominantly in mesenchyme (7,8).…”

“…We demonstrated antisense LGL1 inhibition of airway branching in rat lung explant culture (9), suggesting that lgl1 stimulates airway branching morphogenesis. Maximal fetal GC-responsive LGL1 expression, however, occurs at gestational d 20 -21 in the rat, when branching of conducting airways is complete (7). At this time, mesenchymal lgl1 concentrates in the smooth muscle ␣-actin-positive myofibroblasts, located adjacent to the epithelium, that regulate the formation of new alveolar units (9).…”

Cochlin in the eye: Functional implications

“…Evidence suggests that FCH domains are involved in antibody-independent host defense. For example, Lgl1 is expressed in fetal lungs coincident with the production of pulmonary surfactant and Lgl1-like surfactant proteins, SP-A and SP-D, that may serve to protect the lung against pathogens (Kaplan et al, 1999). Limulus factor C is a trypsin-type serine protease, activated upon binding to LPS in its zymogen state.…”

Cochlin and glaucoma: A mini-review

“…While the function of the FCH domain in cochlin remains to be elucidated, in other proteins this domain is involved in antibody-independent host defense. For example, Lgl1 is expressed in fetal lungs coincident with the production of pulmonary surfactant and it has been suggested that Lgl1-like surfactant proteins SP-A and SP-D serve to protect the lung from pathogens (Kaplan et al, 1999). Limulus factor C is a trypsin-type serine protease, activated upon binding to lipopolysaccharides in its zymogen state.…”