Rezgui Dellel, Williams Christopher, Savage Sharon A, Prince Stuart N, Zaccheo Oliver J, Jones E Yvonne, Crump Matthew P, Hassan A Bassim
Cancer Research UK Tumour Growth Control Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford, UK.
J Mol Endocrinol. 2009 Apr;42(4):341-56. doi: 10.1677/JME-08-0154. Epub 2009 Feb 10.
The mannose 6-phosphate/IGF 2 receptor (IGF2R) is comprised of 15 extra-cellular domains that bind IGF2 and mannose 6-phosphate ligands. IGF2R transports ligands from the Golgi to the pre-lysosomal compartment and thereafter to and from the cell surface. IGF2R regulates growth, placental development, tumour suppression and signalling. The ligand IGF2 is implicated in the growth phenotype, where IGF2R normally limits bioavailability, such that loss and gain of IGF2R results in increased and reduced growth respectively. The IGF2R exon 34 (5002A>G) polymorphism (rs629849) of the IGF2 specific binding domain has been correlated with impaired childhood growth (A/A homozygotes). We evaluated the function of the Gly1619Arg non-synonymous amino acid modification of domain 11. NMR and X-ray crystallography structures located 1619 remote from the ligand binding region of domain 11. Arg1619 was located close to the fibronectin type II (FnII) domain of domain 13, previously implicated as a modifier of IGF2 ligand binding through indirect interaction with the AB loop of the binding cleft. However, comparison of binding kinetics of IGF2R, Gly1619 and Arg1619 to either IGF2 or mannose 6-phosphate revealed no differences in 'on' and 'off' rates. Quantitative PCR, (35)S pulse chase and flow cytometry failed to demonstrate altered gene expression, protein half-life and cell membrane distribution, suggesting the polymorphism had no direct effect on receptor function. Intronic polymorphisms were identified which may be in linkage disequilibrium with rs629849 in certain populations. Other potential IGF2R polymorphisms may account for the correlation with childhood growth, warranting further functional evaluation.
甘露糖6-磷酸/胰岛素样生长因子2受体（IGF2R）由15个细胞外结构域组成，这些结构域可结合IGF2和甘露糖6-磷酸配体。IGF2R将配体从高尔基体转运至溶酶体前区室，然后往返于细胞表面。IGF2R调节生长、胎盘发育、肿瘤抑制和信号传导。配体IGF2与生长表型有关，正常情况下IGF2R会限制其生物利用度，因此IGF2R的缺失和增加分别会导致生长增加和减少。IGF2特异性结合域的IGF2R外显子34（5002A>G）多态性（rs629849）与儿童生长发育受损有关（A/A纯合子）。我们评估了第11结构域中Gly1619Arg非同义氨基酸修饰的功能。核磁共振和X射线晶体学结构显示1619远离第11结构域的配体结合区域。Arg1619靠近第13结构域的纤连蛋白II型（FnII）结构域，此前被认为是通过与结合裂隙的AB环间接相互作用来调节IGF2配体结合的修饰因子。然而，比较IGF2R、Gly1619和Arg1619与IGF2或甘露糖6-磷酸的结合动力学发现，“结合”和“解离”速率没有差异。定量PCR、（35）S脉冲追踪和流式细胞术未能证明基因表达、蛋白质半衰期和细胞膜分布发生改变，这表明该多态性对受体功能没有直接影响。已鉴定出内含子多态性，在某些人群中可能与rs629849处于连锁不平衡状态。其他潜在的IGF2R多态性可能解释了与儿童生长的相关性，需要进一步的功能评估。
