Effect of tyrosine kinase inhibition on surfactant protein A gene expression during human lung development

Downregulation of the epidermal growth factor receptor by human cytomegalovirus infection in human fetal lung fibroblasts

Epidermal growth factor plays a key role in late fetal lung development and differentiation as well as in regulating surfactant protein A synthesis, which is involved in innate immunity of the lung. Here we show that human cytomegalovirus (HCMV), a known lung pathogen in connatal and postnatal infection of neonates as well as transplant recipients, completely down-regulates EGF receptor (EGF-R) on the surface of human fetal lung fibroblasts. Inhibition of EGF-R synthesis occurs on the transcriptional rather than on the posttranscriptional level. The effect essentially depends on expression of viral immediate early and/or early genes, as binding of ultraviolet light-inactivated virus to the cells had no effect on EGF-R expression. Furthermore, the anti-HCMV drug ganciclovir, which blocks HCMV DNA replication and late gene expression, cannot overcome HCMV-mediated inhibition of EGF-R, suggesting that immediate early or early gene products may be responsible for down-regulation of EGF-R. Interestingly, the glucocorticoid dexamethasone, which is used for its antiinflammatory action to prevent chronic lung disease in preterm infants, promotes HCMV-associated downregulation of the EGF-R by stimulation of viral gene expression. From these data it can be hypothesized that the pathogenesis of HCMV lung infection involves down-regulation of EGF-R and that congenital HCMV infection may cause retardation in lung maturation and surfactant protein synthesis.

Immunocytochemical localization of epidermal growth factor receptor in early embryos of the Japanese medaka fish (Oryzias latipes)

This study was undertaken to localize epidermal growth factor receptor (EGFR) during early development of Japanese medaka embryos using immunocytochemistry. Specific staining was observed in all stages studied. All of the cells of the embryonic disc from the germinal disc (1 cell) through the late high blastula stages stained moderately for EGFR. Beginning with the flat blastula stage, the surface and lateral cells of the embryonic disc and the cells migrating around the yolk stained intensely for EGFR, and this continued throughout the study period. The presence of the keel at the late gastrula stage did not affect the moderate staining of the majority of the embryonic disc cells. When somites first appeared, the keel region stained less intensely than before, but scattered individual cells stained intensely for EGFR. Embryos with 12 somites had a neural tube that was lightly stained except for a few intensely stained individual cells. The neural tube, notochord and somites in 24-somite embryos lacked immunostaining. However, the surface epithelium, aorta, intestinal epithelium and pronephric duct demonstrated EGFR immunostaining. This study demonstrates that EGFR is present during medaka development and supports the hypothesis that EGFR ligands are important during cleavage, gastrulation and early organogenesis.

BR22, a novel protein, interacts with thyroid transcription factor-1 and activates the human surfactant protein B promoter

Surfactant protein (SP)-B expression is restricted to type II pneumocytes and Clara cells in the lung. Previously, a promoter region of human SP-B gene from -64 to -118 has been identified as critical for the tissue-specific expression of this gene. Two cis-elements for thyroid transcription factor (TTF)-1 and hepatocyte nuclear factor (HNF)-3alpha binding were found within this area. Using an oligonucleotide fragment, we incorporated this region sequence into the promoter of a HIS3 reporter gene in yeast. With this modified yeast a human lung complementary DNA (cDNA) library was screened for DNA-binding proteins, other than TTF-1 and HNF-3alpha, that interacted with this promoter segment. A cDNA clone encoding a novel polypeptide, BR22, was identified that activated the reporter gene expression in yeast. This gene is expressed in many tissues and encodes a protein with bipartite nuclear localization signals. Studies using in vivo yeast two-hybrid analysis, in vitro protein-protein interactions, and coimmunoprecipitation analyses demonstrated that BR22 formed a protein complex with TTF-1. In vivo cotransfection studies further indicated that BR22 could act with TTF-1 to synergistically activate the SP-B promoter in mammalian cells. Our data suggest that BR22 is a TTF-1-associated protein. Through a protein-protein interaction with TTF-1, BR22 can form a complex and activate the human SP-B promoter in vivo.

Antisense inhibition of epidermal growth factor receptor decreases expression of human surfactant protein A

Epidermal growth factor (EGF) stimulates surfactant protein A (SP-A) synthesis in fetal lung tissue through ligand binding to the EGF receptor. We hypothesized that inhibition of EGF receptor messenger RNA (mRNA) would block SP-A expression in human fetal lung tissue during alveolar type II cell differentiation in vitro. Midtrimester human fetal lung explants were maintained in serum-free Waymouth's medium for 3 to 5 d in the presence or absence of an antisense 18-mer phosphorothioate oligonucleotide (ON) complementary to the initiation codon region of EGF receptor mRNA. Sense and scrambled ONs similarly modified were used as additional controls. The concentration of EGF receptor mRNA was semiquantitatively determined by reverse transcriptase/polymerase chain reaction (RT-PCR). We found a significant 3-fold decrease in EGF receptor mRNA levels in the antisense-treated groups compared with the control group with no effect in the sense condition. Immunohistochemical staining revealed a decrease in the amount of staining for EGF receptor protein in distal pulmonary epithelial cells in the antisense-treated groups compared with either control or sense conditions. Treatment with antisense EGF receptor ON decreased both SP-A mRNA and protein compared with controls with no effect in the sense condition. The ONs did not affect tissue viability as measured by the release of lactate dehydrogenase. We conclude that selective degradation of EGF receptor mRNA with antisense ON treatment results in a decrease in SP-A expression in human fetal lung. These findings support the critical importance of the EGF receptor for the regulation of SP-A gene expression during human alveolar type II cell differentiation.