Division of Molecular and Clinical Medicine, University of Dundee, Dundee, UK.
MRC Protein Phosphorylation and Ubiquitylation Unit, University of Dundee, Dundee, UK.
Sci Rep. 2017 Dec 15;7(1):17682. doi: 10.1038/s41598-017-17087-6.
Glycogen synthase kinase-3 (GSK3) regulates many physiological processes through phosphorylation of a diverse array of substrates. Inhibitors of GSK3 have been generated as potential therapies in several diseases, however the vital role GSK3 plays in cell biology makes the clinical use of GSK3 inhibitors potentially problematic. A clearer understanding of true physiological and pathophysiological substrates of GSK3 should provide opportunities for more selective, disease specific, manipulation of GSK3. To identify kinetically favourable substrates we performed a GSK3 substrate screen in heart tissue. Rab-GTPase binding effector protein 2 (RABEP2) was identified as a novel GSK3 substrate and GSK3 phosphorylation of RABEP2 at Ser200 was enhanced by prior phosphorylation at Ser204, fitting the known consensus sequence for GSK3 substrates. Both residues are phosphorylated in cells while only Ser200 phosphorylation is reduced following inhibition of GSK3. RABEP2 function was originally identified as a Rab5 binding protein. We did not observe co-localisation of RABEP2 and Rab5 in cells, while ectopic expression of RABEP2 had no effect on endosomal recycling. The work presented identifies RABEP2 as a novel primed substrate of GSK3, and thus a potential biomarker for GSK3 activity, but understanding how phosphorylation regulates RABEP2 function requires more information on physiological roles of RABEP2.
糖原合酶激酶-3（GSK3）通过磷酸化多种底物来调节许多生理过程。GSK3 的抑制剂已被作为几种疾病的潜在治疗方法而产生，然而 GSK3 在细胞生物学中所起的重要作用使得 GSK3 抑制剂的临床应用可能存在问题。对 GSK3 的真正生理和病理生理底物有更清楚的了解，应该为更具选择性、针对特定疾病的 GSK3 操作提供机会。为了鉴定动力学有利的底物，我们在心脏组织中进行了 GSK3 底物筛选。Rab-GTPase 结合效应蛋白 2（RABEP2）被鉴定为一种新的 GSK3 底物，并且 RABEP2 的 Ser200 处的 GSK3 磷酸化在前 Ser204 磷酸化的情况下增强，符合 GSK3 底物的已知共有序列。这两个残基在细胞中都被磷酸化，而只有 GSK3 抑制后 Ser200 磷酸化减少。RABEP2 的功能最初被鉴定为 Rab5 结合蛋白。我们没有观察到 RABEP2 和 Rab5 在细胞中的共定位，而 RABEP2 的异位表达对内体再循环没有影响。目前的工作确定 RABEP2 是 GSK3 的一种新型引发底物，因此是 GSK3 活性的潜在生物标志物，但要了解磷酸化如何调节 RABEP2 的功能，需要更多关于 RABEP2 生理作用的信息。
