Modulation of gene expression by hypoxia in human umbilical cord vein endothelial cells: A transcriptomic and proteomic study.

Hypoxia is a characteristic feature of many human pathologies, including cancer. The sustained proliferation rate of tumor cells leads to alterations of the tumor microenvironment, that progressively becomes more acidic, nutrient-deprived, and hypoxic. The reduced partial pressure of oxygen triggers the onset of an adaptive response, aimed at increasing the local oxygen concentration by several complementary actions. Although directly exposed to the blood stream, endothelial cells lining the vascular lumen in tumors also can be exposed to hypoxia and therefore can contribute to the onset of the adaptive response that leads to tumor angiogenesis. Aiming at getting a detailed insight into the oxygen-dependent regulation of the transcriptional program of vascular endothelial cells and at identifying new relevant markers that may be used as targets for therapeutic intervention in tumor angiogenesis, we have performed a broad-range transcriptomic analysis, using the Affymetrix HG-U133A Gene Chips, of mRNA expression levels in human umbilical cord vein endothelial cells (HUVEC), exposed in vitro to hypoxia for different time periods. The transcriptomic analysis was complemented by a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of mRNA levels and alternative splicing for some selected extracellular matrix protein genes, and by a proteomic analysis, using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) and tandem mass spectrometry for protein separation and identification, of hypoxic and normoxic HUVEC whole-cell lysates and subcellular fractions. Our analysis confirmed previous findings on genes whose expression is regulated by oxygen concentration but also identified new genes (e.g., CXCR4, claudin 3, CD24, tetranectin, Del-1, procollagen lysyl hydroxylase 1 and 2) which are transcriptionally upregulated in hypoxic conditions.