# Regulation of Pleiotrophin and PTPRZ1 Expression by Hypoxia to Restrict Hypoxia-Induced Cell Migration

## TL;DR

This study shows how hypoxia limits cell migration by regulating the expression of PTN and PTPRZ1 in tumor and endothelial cells.

## Contribution

The novel finding is that hypoxia-induced PTN and PTPRZ1 act to restrict hypoxia's stimulatory effects on cell migration.

## Key findings

- Hypoxia increases PTN expression in ανβ3 integrin-expressing cells via HIF and AP-1.
- PTN negatively affects hypoxia-induced cell proliferation and migration.
- PTPRZ1 expression is upregulated by hypoxia and limits HIF-1α activation in endothelial cells.

## Abstract

Hypoxia regulates gene expression to support tumor cell invasion and angiogenesis. Hypoxia-inducible transcription factors (HIFs) play a major role in the hypoxia effects through interactions with other transcription factors, such as AP-1. Pleiotrophin (PTN) acts through protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) and regulates cell migration in a manner that depends on ανβ3 integrin expression. The present study shows that hypoxia or chemical hypoxia increases the PTN expression in endothelial and glioblastoma cells that express ανβ3 integrin in a HIF- and AP-1-dependent manner to negatively impact the stimulatory effect of hypoxia on endothelial cell proliferation and migration. The expression of PTPRZ1 is also enhanced by hypoxia, is HIF-dependent, and limits the activation of HIF-1α in endothelial cells. In conclusion, hypoxia or chemical hypoxia regulates PTN and PTPRZ1 expression to restrict its stimulatory effects on endothelial and cancer cells.

Background/Objectives: In the tumor microenvironment, hypoxia regulates genes that support tumor cell invasion and angiogenesis under the control of the hypoxia-inducible transcription factors (HIFs). Pleiotrophin (PTN) is a secreted protein that activates cell migration in endothelial and cancer cells that express ανβ3 integrin but has inhibitory effects in cells that do not express ανβ3 integrin. In both cases, the protein tyrosine phosphatase receptor zeta 1 (PTPRZ1) seems to mediate the effects of PTN. In the present work, we studied the effect of hypoxia on PTN and PTPRZ1 expression and the functional consequences of this effect. Methods: Western blot, quantitative real-time PCR, and luciferase assays were used to study the impact of hypoxia at the protein, mRNA, and transcriptional levels, respectively. Decoy oligonucleotides (ODNs), siRNA technology, and plasmid overexpression were used to study the involvement of the transcription factors studied. Functional assays were used to study the effect of hypoxia on cell proliferation and migration. Results: Hypoxia increases PTN expression through the transcriptional activation of the corresponding gene in ανβ3 integrin-expressing cells. The transcription factors HIF-1α, HIF-2α, and AP-1 mediate the up-regulation of PTN by hypoxia. Functional assays in endothelial cells from PTN knockout mice or endothelial and cancer cells following the downregulation of PTN expression showed that PTN negatively affects chemical hypoxia-induced cell proliferation and migration. In cancer cells that do not express ανβ3 integrin, hypoxia or chemical hypoxia inhibits PTN expression in a HIF-1α-, HIF-2α-, and AP-1-independent manner. The expression of PTPRZ1 is up-regulated by chemical hypoxia, is HIF-1α- and HIF-2α-dependent, and seems to limit the activation of HIF-1α, at least in endothelial cells. Conclusions: Hypoxia or chemical hypoxia regulates PTN and PTPRZ1 expressions to restrict the stimulatory effects of hypoxia on endothelial and cancer cell migration.