Placenta growth factor gene expression is induced by hypoxia in fibroblasts: A central role for metal transcription factor-1

Placenta growth factor (PlGF) is a mitogen for endothelial cells that can p otentiate the growth and permeabilizing effects on endothelium of vascular endothelial growth factor, Here we report that hypoxia induces the expressi on of both PlGF mRNA and protein in immortalized/transformed mouse embryoni c fibroblasts (mEFs) and in NIH 3T3 cells. Importantly, the magnitude of th e induction of PlGF expression by hypoxia is enhanced by the presence? of o ncogenic Pas. To investigate the transcriptional component of hypoxia-induc ible PlGF expression, we cloned and sequenced a 1350-bp fragment of the 5'- flanking region of the mouse gene. Analysis of the promoter region indicate d the presence of putative consensus sequences for known hypoxia-responsive regulatory sites, including metal response elements and Spl-like sites. In the present study, we show that the induction of PlGF expression by hypoxi a is dependent on the presence of the metal response element-binding transc ription factor 1 (MTF-1), Thus, in mEFs with targeted deletions of both MTF -1 alleles, hypoxia-induced increases of PlGF mRNA and protein levels were greatly attenuated compared with those in wild-type mEFs. Moreover, transie nt transfection of a PlGF promoter reporter gene into NM 3T3 cells resulted in hypoxia-responsive transcriptional activation of the reporter, Finally, ectopic expression of MTF-I resulted in increased basal transcriptional ac tivity of a PlGF promoter reporter. Together, these findings demonstrate th at the PlGF gene is responsive to hypoxia and that this response is mediate d by MTF-I. It remains to be determined whether this activation is the resu lt of direct and/or indirect transcriptional activation by MTF-I. The stimu latory effect of oncogenic Pas on the induction of PlGF expression in hypox ic cells suggests that PlGF could be an important proangiogenic factor in t he tumor microenvironment.