Varghese Leila N, Zhang Jian-Guo, Young Samuel N, Willson Tracy A, Alexander Warren S, Nicola Nicos A, Babon Jeffrey J, Murphy James M
The Walter and Eliza Hall Institute of Medical Research , Parkville, Victoria , Australia and.
Growth Factors. 2014 Feb;32(1):18-26. doi: 10.3109/08977194.2013.874347. Epub 2014 Jan 20.
Activation of the cell surface receptor, c-Mpl, by the cytokine, thrombopoietin (TPO), underpins megakaryocyte and platelet production in mammals. In humans, mutations in c-Mpl have been identified as the molecular basis of Congenital Amegakaryocytic Thrombocytopenia (CAMT). Here, we show that CAMT-associated mutations in c-Mpl principally lead to defective receptor presentation on the cell surface. In contrast, one CAMT mutant c-Mpl, F104S, was expressed on the cell surface, but showed defective TPO binding and receptor activation. Using mutational analyses, we examined which residues adjacent to F104 within the membrane-distal cytokine receptor homology module (CRM) of c-Mpl comprise the TPO-binding epitope, revealing residues within the predicted Domain 1 E-F and A-B loops and Domain 2 F'-G' loop as key TPO-binding determinants. These studies underscore the importance of the c-Mpl membrane-distal CRM to TPO-binding and suggest that mutations within this CRM that perturb TPO binding could give rise to CAMT.
细胞因子血小板生成素（TPO）对细胞表面受体c-Mpl的激活是哺乳动物巨核细胞和血小板生成的基础。在人类中，已确定c-Mpl的突变是先天性无巨核细胞血小板减少症（CAMT）的分子基础。在此，我们表明，c-Mpl中与CAMT相关的突变主要导致细胞表面受体呈递缺陷。相比之下，一种CAMT突变体c-Mpl，即F104S，在细胞表面表达，但显示出TPO结合和受体激活缺陷。通过突变分析，我们研究了c-Mpl膜远端细胞因子受体同源模块（CRM）中与F104相邻的哪些残基构成了TPO结合表位，揭示了预测的结构域1的E-F和A-B环以及结构域2的F'-G'环内的残基是关键的TPO结合决定因素。这些研究强调了c-Mpl膜远端CRM对TPO结合的重要性，并表明该CRM内干扰TPO结合的突变可能导致CAMT。
