Journal of Cell Science：红细胞发育调控新机制

　　

北京大学分子医学所熊敬维教授课题组与珅奥基公司孟坤博士合作的研究成果“Protein Tyrosine Phosphatase PTPN9 Regulates Erythroid Cell Development through STAT3 Dephosphorylation in Zebrafish”（酪氨酸蛋白激酶PTPN9通过去磷酸化STAT3调节斑马鱼的红细胞发育），近日在国际学术杂志Journal of Cell Science在线发表（April 11, 2014 doi: 10.1242/jcs.145367）。

酪氨酸蛋白激酶PTP家族在细胞增殖、分化和迁移相关的信号通路中扮演重要角色。前期研究表明，人PTP9通过去磷酸化不同蛋白，起到促进同型囊泡融合、介导肝细胞中胰岛素信号转导、抑制乳腺癌细胞生长、调控内皮细胞功能等多种作用。PTPN9与STAT3直接相互作用，并且在乳腺癌细胞中调节STAT3去磷酸化。STAT3是一个重要的细胞转录因子，在许多肿瘤中发挥极其重要的作用。STAT3已被报道与肿瘤干细胞密切相关，是治疗和预后的一个重要生物标志物。

熊敬维教授和孟坤博士的研究表明，斑马鱼中的Ptpn9a，而非Ptpn9b，在胚胎形成的红细胞发育中起重要作用。敲除ptpn9a导致STAT3磷酸化水平显著提高，而高水平磷酸化STAT3抑制了GATA1和ZBP-89对红细胞基因表达的调控功能。在人细胞株K562中针对同源蛋白PTPN9的体外实验也得到一致结果。基于以上结果推测，PTPN9通过破坏抑制性复合体pSTAT3- GATA1- ZBP89 而在红细胞生成中起重要作用，这为了解ptpn9a在发育过程造血作用中的机理提供了全新的细胞水平和分子水平的参考，也为STAT3药物开发及肿瘤干细胞治疗的预后提供重要的依据。

该论文的第一作者是北京大学分子医学所的Ye Bu博士，熊敬维教授和孟坤博士为共同通讯作者。

摘要：
Protein tyrosine phosphatases (PTPs) such as SHP-1, SHP-2 and CD45 are involved in hematopoiesis, but the function of many PTPs is not well characterized in vivo. Here we have identified Ptpn9a, an ortholog of human PTPN9, as a crucial regulator of erythroid cell development in zebrafish embryos. ptpn9a, but not ptpn9b, was expressed in the posterior lateral plate mesoderm and intermediate cell mass, two primitive hematopoietic sites during zebrafish embryogenesis. Morpholino-mediated knockdown of ptpn9a depleted erythrocytes by inhibiting erythroid cell maturation without affecting erythroid proliferation and apoptosis. Consistently, both dominant-negative PTPN9C515S and PTPN9 siRNA inhibited erythroid differentiation in human K562 cells. Mechanistically, depletion of PTPN9 in zebrafish embryos in vivo or K562 cells in vitro increased phosphorylated STAT3 (pSTAT3), and the hyper-phosphorylated STAT3 entrapped and prevented GATA1 and ZBP-89 from regulating erythroid gene expression. These findings imply that PTPN9 plays an important role in erythropoiesis by disrupting an inhibitory complex of pSTAT3, GATA1 and ZBP-89, providing new cellular and molecular insights of ptpn9a into developmental hematopoiesis.

结论：
ptpn9a is expressed in the primitive hematopoietic sites during zebrafish embryogenesis. Knockdown of ptpn9a diminishes the number of primitive erythrocytes. ptpn9a knockdown has no effect on erythroid cell proliferation and apoptosis in primitive hematopoiesis. PTPN9 is required for erythroid cell maturation. Increased STAT3 phosphorylation by knockdown of PTPN9 enhances formation of the STAT3-GATA1-ZBP-89 complex. Dephosphorylation of STAT3 by PTPN9 contributes to erythroid cell maturation.