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 ανβ3integrin but has inhibitory effects in cells that do not express ανβ3integrin. 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 ανβ3integrin-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 ανβ3integrin, 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.
背景/目的：在肿瘤微环境中，缺氧通过缺氧诱导转录因子（HIFs）调控支持肿瘤细胞侵袭和血管生成的基因。多效生长因子（PTN）是一种分泌蛋白，在表达ανβ3整合素的内皮细胞和癌细胞中能激活细胞迁移，但对不表达ανβ3整合素的细胞则具有抑制作用。在这两种情况下，蛋白酪氨酸磷酸酶受体Z1（PTPRZ1）似乎介导了PTN的作用。本研究探讨了缺氧对PTN和PTPRZ1表达的影响及其功能后果。方法：分别采用蛋白质印迹、实时定量PCR和荧光素酶报告基因检测技术，在蛋白、mRNA和转录水平研究缺氧的影响。通过诱饵寡核苷酸、siRNA技术和质粒过表达技术，研究相关转录因子的参与机制。采用功能实验分析缺氧对细胞增殖和迁移的影响。结果：在表达ανβ3整合素的细胞中，缺氧通过转录激活相应基因上调PTN表达。转录因子HIF-1α、HIF-2α和AP-1介导了缺氧对PTN的上调作用。对PTN敲除小鼠的内皮细胞或下调PTN表达的内皮细胞与癌细胞进行的功能实验表明，PTN对化学缺氧诱导的细胞增殖和迁移具有负向调控作用。在不表达ανβ3整合素的癌细胞中，缺氧或化学缺氧以不依赖HIF-1α、HIF-2α和AP-1的方式抑制PTN表达。PTPRZ1的表达受化学缺氧上调，该过程依赖HIF-1α和HIF-2α，且似乎能限制HIF-1α的激活（至少在内皮细胞中）。结论：缺氧或化学缺氧通过调控PTN和PTPRZ1的表达，限制缺氧对内皮细胞和癌细胞迁移的刺激作用。
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