PubMed · 9172603
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S Kakuta, S Usutani, M Sirai, M Nagase. 1997. [Selectivity index].. https://pubmed.ncbi.nlm.nih.gov/9172603/
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Neonatal respiratory function depends on the development of a well-formed pulmonary capillary bed. Vascular endothelial growth factor (VEGF) is a potent inducer of endothelial cell growth and angiogenesis. High levels of VEGF protein and messenger RNA (mRNA) have been detected in the developing lung, suggesting that VEGF plays a role in the development of the pulmonary capillary bed. To begin to understand the role of VEGF in human lung development, we explored the regulation of VEGF gene expression and the localization of VEGF protein and mRNA in a model of the developing human lung. VEGF protein and mRNA were detected in midtrimester human fetal lung tissue, and their levels increased with time in explant culture. VEGF protein and mRNA were increased by the maintenance of human fetal lung explants in 2% O2 environments compared with 20% O2 environments. VEGF mRNA levels were found to be increased by cyclic adenosine monophosphate (cAMP) in explants that were incubated in 20% O2, but not in those incubated in 2% O2. Immunostaining for VEGF protein demonstrated localization primarily in airway epithelial cells in midtrimester human fetal lung tissue. Immunostaining for VEGF increased with incubation of human fetal lung explants in 2% and 20% O2. Interestingly, VEGF protein was localized primarily in the basement membrane subjacent to airway epithelial cells after 4 d of incubation in 20% O2. Incubation of tissues in the presence of dibutyryl cAMP resulted in an increase in immunostaining for VEGF, primarily in the basement membranes of prealveolar ducts in 20% O2-treated tissues. In situ hybridization studies indicated that VEGF mRNA was present in both mesenchymal cells and airway epithelial cells. These data suggest that VEGF gene expression is regulated by both oxygen and cAMP in the developing human lung. The detection of VEGF mRNA and protein in distal airway epithelial cells and the detection of VEGF protein in the basement membrane subjacent to the airway epithelial cells suggest that translocation of VEGF protein occurs after its synthesis in the epithelium. Localization of VEGF to the basement membrane of airway epithelial cells may be important for directing capillary development in the human lung.
Anchorage and growth factor independence are cardinal features of the transformed phenotype. Although it is logical that the two pathways must be coregulated in normal tissues to maintain homeostasis, this has not been demonstrated directly. We showed previously that down-modulation of beta1-integrin signaling reverted the malignant behavior of a human breast tumor cell line (T4-2) derived from phenotypically normal cells (HMT-3522) and led to growth arrest in a three-dimensional (3D) basement membrane assay in which the cells formed tissue-like acini (14). Here, we show that there is a bidirectional cross-modulation of beta1-integrin and epidermal growth factor receptor (EGFR) signaling via the mitogen-activated protein kinase (MAPK) pathway. The reciprocal modulation does not occur in monolayer (2D) cultures. Antibody-mediated inhibition of either of these receptors in the tumor cells, or inhibition of MAPK kinase, induced a concomitant down-regulation of both receptors, followed by growth-arrest and restoration of normal breast tissue morphogenesis. Cross-modulation and tissue morphogenesis were associated with attenuation of EGF-induced transient MAPK activation. To specifically test EGFR and beta1-integrin interdependency, EGFR was overexpressed in nonmalignant cells, leading to disruption of morphogenesis and a compensatory up-regulation of beta1-integrin expression, again only in 3D. Our results indicate that when breast cells are spatially organized as a result of contact with basement membrane, the signaling pathways become coupled and bidirectional. They further explain why breast cells fail to differentiate in monolayer cultures in which these events are mostly uncoupled. Moreover, in a subset of tumor cells in which these pathways are misregulated but functional, the cells could be "normalized" by manipulating either pathway.
The basement membrane (BM) underlying the epithelium of the intestine is generally believed to be of both epithelial and mesenchymal origin but the exact contribution of each tissue has not been directly examined in the human. In this study, we have used a newly described procedure to dissociate the human intestine into pure epithelial and corresponding mesenchymal fractions. Northern blot and RT-PCR analyses of the fractions for the presence of transcripts encoding extracellular matrix molecules revealed that the epithelium produces the formal BM molecules such as the alpha 1, alpha 2, and beta 1 chains of laminin-1 and laminin-2 and the alpha 5(IV) and alpha 6(IV) chains of collagen as well as fibronectin, a BM-associated molecule. Interestingly, the alpha 1(IV) chain of collagen, which associates with the alpha 2(IV) chain to form the main BM collagen network, as well as tenascin-C and decorin, two BM-associated molecules, was found to be exclusively of mesenchymal origin. Taken together, these data support the concept that in the human, as in experimental animals, the intestinal BM is composed of components produced from both the epithelium and the mesenchyme.