Activation/Proliferation-associated Protein 2 (Caprin-2) Positively Regulates CDK14/Cyclin Y-mediated Lipoprotein Receptor-related Protein 5 and 6 (LRP5/6) Constitutive Phosphorylation*
- From the State Key Laboratory of Molecular Biology, Chinese Academy of Sciences Center for Excellence in Molecular Cell Science, Innovation Center for Cell Signaling Network, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
- ↵1 To whom correspondence may be addressed. E-mail: xmsong01{at}sibcb.ac.cn.
- ↵2 To whom correspondence may be addressed. E-mail: lli{at}sibs.ac.cn.
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Edited by Xiao-Fan Wang
Abstract
Low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) are co-receptors for Wnt ligands. Upon ligand binding, LRP5/6 undergo glycogen synthase kinase 3 (GSK3)/casein kinase I (CKI)-mediated phosphorylation at multiple PPP(S/T)P motifs in the intracellular domain, which is essential for canonical Wnt signal transduction. On the other hand, in the Wnt-off state, the mitosis-specific CDK14-Cyclin Y kinase complex phosphorylates Ser-1490 of LRP5/6 at G2/M, thereby priming the receptor for Wnt-induced phosphorylation. However, it remains unclear how CDK14/Cyclin Y is recruited to LRP5/6 and whether there are other cofactors involved in this process. Previously, we identified Caprin-2 as a positive regulator of canonical Wnt signaling by promoting GSK3-depedent LRP5/6 phosphorylation upon Wnt stimulation. Here we uncovered that Caprin-2 positively regulates constitutive LRP5/6 Ser-1490 phosphorylation by complexing with CDK14/Cyclin Y. Caprin-2-mediated LRP5/6 phosphorylation is cell cycle-dependent in a pattern similar to that of CDK14/Cyclin Y-dependent LRP5/6 phosphorylation. Moreover, knockdown of Caprin-2 disrupts not only the interaction between CDK14 and Cyclin Y but also the interaction between CDK14/Cyclin Y and LRP6. Overall, our findings revealed an unrecognized role of Caprin-2 in facilitating LRP5/6 constitutive phosphorylation at G2/M through forming a quaternary complex with CDK14, Cyclin Y, and LRP5/6.
Footnotes
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↵* This work was supported by the National Natural Science Foundation of China (Grants 31530094, 31230044 and 31100532) and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grants XDB19000000 and XDA12010301). The authors declare that they have no conflicts of interest with the contents of this article.
- Received June 21, 2016.
- Revision received November 3, 2016.
- © 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
