Insulin-like growth factor binding protein-4 accumulation is negatively correlated with growth rate in TM-3 cells

Regulation of cell proliferation by insulin-like growth factor 1 in hyperoxia-exposed neonatal rat lung

Hyperoxic exposure of the developing lung leads to characteristic peribronchial and mesenchymal fibroproliferative changes. We hypothesize that O2-induced changes in the neonatal lung are mediated by Insulin-like growth factor 1 (IGF-1) and IGF-1 receptor (IGF-1R). Lung explant cultures were prepared from 3-day-old neonatal rat pups and exposed to room air or 95% O2 for 72 h. Western blots and immunohistochemistry were used to determine if hyperoxia stimulated IGF-1 and IGF-1R, and to identify the cell types involved. Retinoic acid was used to learn if this would inhibit oxygen-induced cell proliferation. Hyperoxia induced a significant increase in thymidine incorporation (control, 54 +/- 9; hyperoxia, 254 +/- 24 dpm/nM DNA; mean +/- SEM; N = 3; P < 0.05). This was inhibited by 5 x 10(-5) M RA (149 +/- 18 dpm/nM DNA; P < 0.05) and by anti-IGF-1 antibody (115 +/- 25 dpm/nM DNA; P < 0.05; N = 3). BrdU labeling in the mesenchymal cells was significantly increased in mesenchymal cells after exposure to oxygen (91% higher than the room air control) but not in epithelial cells. This increase was inhibited in the presence of retinoic acid. Western blots showed IGF-1 protein was increased after 72 h of O2 exposure compared to room air exposure (57 +/- 7 compared to 32 +/- 5 densitometric units; P < 0.05; N = 3). The increase was inhibited when the cultures were exposed to 95% O2 in the presence of anti-IGF-1 antibody (28 +/- 4; P < 0.05; N = 3). IGF-1 protein decreased in the presence of retinoic acid after oxygen exposure but not in room air. Immunostaining of O2-exposed lung showed IGF-1 was most abundant in airway and alveolar epithelial cells. We conclude that hyperoxia increases cell proliferation by stimulating IGF-1 in the neonatal rat lung. Interaction of IGF-1 and IGF-1R is an important cell-cell communication mechanism in the developmental and repair processes of hyperoxic neonatal lung injury.

Analyses of p53 target genes in the human genome by bioinformatic and microarray approaches

The completion of the human genome sequence (International Human Genome Sequence Consortium (2001) Nature 409, 860-921; Venter, J. C., et al. (2001) Science 291, 1304-1351) allows for new ways to analyze global cellular regulatory mechanisms. Here we present a strategy to identify genes regulated by specific transcription factors in the human genome, and apply it to p53. We first collected promoters or introns of all genes available using two methods: GenBank(TM) annotation and a computationally derived transcript map. 4,852 genes analyzed in this way contained at least one p53 consensus binding sequence. Of 13 genes randomly selected for mRNA analysis, 11 were shown to respond to p53 expression. Five promoters were analyzed by chromatin immunoprecipitation, which revealed that all were bound by p53 in vivo. We then analyzed 33,615 unique human genes on cDNA microarrays, identifying 1,501 genes that respond to p53 expression. A parameter was derived that demonstrates that in silico prediction greatly enriches for genes that are activated and repressed by p53 and assists us to suggest other signaling pathways that may be connected to p53. The methods shown here illustrate a novel approach to analysis of global gene regulatory network through the integration of human genomic sequence information and genome-wide gene expression analysis.