DKK1 Activates the PI3K/AKT Pathway via CKAP4 to Balance the Inhibitory Effect on Wnt/-Catenin Signaling and Regulates Wnt3a-Induced MSC Migration

Wnt/beta-catenin signaling plays a crucial role in the migration of mesenchymal stem cells (MSCs). However, our study has revealed an intriguing phenomenon where Dickkopf-1 (DKK1), an inhibitor of Wnt/beta-catenin signaling, promotes MSC migration at certain concentrations ranging from 25 to 100 ng/mL while inhibiting Wnt3a-induced MSC migration at a higher concentration (400 ng/mL). Interestingly, DKK1 consistently inhibited Wnt3a-induced phosphorylation of LRP6 at all concentrations. We further identified cytoskeleton-associated protein 4 (CKAP4), another DKK1 receptor, to be localized on the cell membrane of MSCs. Overexpressing the CRD2 deletion mutant of DKK1 (Delta CRD2), which selectively binds to CKAP4, promoted the accumulation of active beta-catenin (ABC), the phosphorylation of AKT (Ser473) and the migration of MSCs, suggesting that DKK1 may activate Wnt/beta-catenin signaling via the CKAP4/PI3K/AKT cascade. We also investigated the effect of the CKAP4 intracellular domain mutant (CKAP4-P/A) that failed to activate the PI3K/AKT pathway and found that CKAP4-P/A suppressed DKK1 (100 ng/mL)-induced AKT activation, ABC accumulation, and MSC migration. Moreover, CKAP4-P/A significantly weakened the inhibitory effects of DKK1 (400 ng/mL) on Wnt3a-induced MSC migration and Wnt/beta-catenin signaling. Based on these findings, we propose that DKK1 may activate the PI3K/AKT pathway via CKAP4 to balance the inhibitory effect on Wnt/beta-catenin signaling and thus regulate Wnt3a-induced migration of MSCs. Our study reveals a previously unrecognized role of DKK1 in regulating MSC migration, highlighting the importance of CKAP4 and PI3K/AKT pathways in this process. [GRAPHICS]