Hypoxia upregulates expression of human endosialin gene via hypoxia-inducible factor 2

Abstract

Endosialin is a transmembrane glycoprotein selectively expressed in blood vessels and stromal fibroblasts of various human tumours. It has been functionally implicated in angiogenesis, but the factors that control its expression have remained unclear. As insufficient delivery of oxygen is a driving force of angiogenesis in growing tumours, we investigated whether hypoxia regulates endosialin expression. Here, we demonstrate that endosialin gene transcription is induced by hypoxia predominantly through a mechanism involving hypoxia-inducible factor-2 (HIF-2) cooperating with the Ets-1 transcription factor. We show that HIF-2 activates the endosialin promoter both directly, through binding to a hypoxia-response element adjacent to an Ets-binding site in the distal part of the upstream regulatory region, and indirectly, through Ets-1 and its two cognate elements in the proximal promoter. Our data also suggest that the SP1 transcription factor mediates responsiveness of the endosialin promoter to high cell density. These findings elucidate important aspects of endosialin gene regulation and provide a rational frame for future investigations towards better understanding of its biological significance.

Hypoxia Increases Sirtuin 1 Expression in a Hypoxia-inducible Factor-dependent Manner

“…HIF-2 activation of the Sirt1 promoter is probably influenced by other trans-acting factors, besides Sirt1, because mutations in the candidate EBS that flank HRE5 selectively affect HIF-2-mediated, and not HIF-1-mediated, induction of the isolated Sirt1 promoter. The spatial relationship of the HRE and flanking EBS are consistent with that found in other HIF-2-selective HIF target genes (32)(33)(34). Definitive proof of a role for Ets family members in Sirt1 regulation will require further studies.…”

“…2A). One of these candidate HREs, HRE5, also is flanked by candidate ETS-binding sites (EBS), which have previously been shown to confer HIF-2-selective activation (32)(33)(34). To test whether the proximal SIRT1 promoter would respond to HIF activation, we isolated the human SIRT1 proximal promoter and fused it to firefly luciferase coding sequences for use in transient transfection assays with Hep3B and HT1080 cells.…”

The pericyte and stromal cell marker CD248 (endosialin) is required for efficient lymph node expansion

“…This results in an increase in CD248 expression, via hypoxia inducible factor-2a [9], which in turn is required for full expansion of pLN. This is analogous to the previous studies where lack of CD248 inhibited full expansion of abdominal tumours [8].…”

“…An important role for CD248 within tumour stroma has been highlighted in CD248-deficient mice; abdominal tumours implanted into mice lacking CD248 demonstrated reduced growth, invasion and metastasis [8]. This, coupled with the finding that CD248 expression is regulated by hypoxia inducible factor-2a [9], suggests that CD248 may provide an important link between hypoxia and tissue remodelling allowing synchronisation of these processes.We have previously proposed a role for CD248 in development and infection-dependent activation of SLO stroma [10]. Whether CD248 is required for tissue remodelling was not explored nor was its function.…”

Characteristics of human Ewing/PNET sarcoma models

“…Although the biological function of endosialin is incompletely understood beyond evidence that endosialin may interact with the tumor microenvironment67–7072 and play a role in the expression of PDGF and in pericyte function,70 data support the notion that endosialin may play a role in malignancy. Most importantly, endosialin is expressed in sarcomas with poor prognosis and in advanced sarcoma, opening up the possibility that targeting endosialin could offer a therapeutic avenue for the more than 50% of children and adults suffering from sarcomas whose disease cannot be cured with existing treatment modalities 7374…”