Wnt5a induces ROR1 to associate with 14-3-3ζ for enhanced chemotaxis and proliferation of chronic lymphocytic leukemia cells.

Abstract

Wnt5a can activate Rho GTPases in chronic lymphocytic leukemia cells by inducing the recruitment of ARHGEF2 to ROR1. Mass spectrometry on immune-precipitates of Wnt5a-activated ROR1 identified 14-3-3ζ, which was confirmed by co-immunoprecipitation. The capacity of Wnt5a to induce ROR1 to complex with 14-3-3ζ could be blocked in CLL cells treated with cirmtuzumab, a humanized mAb targeting ROR1. Silencing 14-3-3ζ via siRNA impaired the capacity of Wnt5a to: (1) induce recruitment of ARHGEF2 to ROR1, (2) enhance in vitro exchange activity of ARHGEF2, and (3) induce activation of RhoA and Rac1 in CLL cells. Furthermore, CRISPR/Cas9 deletion of 14-3-3ζ in ROR1-negative CLL cell-line MEC1, and in MEC1 cells transfected to express ROR1 (MEC1-ROR1), demonstrated that 14-3-3ζ was necessary for the growth/engraftment advantage of MEC1-ROR1 over MEC1 cells. We identified a binding motif (RSPS857SAS) for 14-3-3ζ on ROR1. Site-directed mutagenesis of ROR1 demonstrated that serine-857 was required for the recruitment of 14-3-3ζ and ARHGEF2 to ROR1, and activation of RhoA and Rac1. Collectively, this study reveals that 14-3-3ζ plays a critical role in Wnt5a/ROR1 signaling leading to enhanced CLL migration and proliferation.Leukemia accepted article preview online, 03 May 2017. doi:10.1038/leu.2017.132.

https://www.ncbi.nlm.nih.gov/pubmed/28465528

Wnt5a induces ROR1 to complex with HS1 to enhance migration of chronic lymphocytic leukemia cells.

Abstract

ROR1 is a conserved, oncoembryonic surface-antigen expressed in chronic lymphocytic leukemia (CLL). We found that ROR1 associates with Hematopoietic-lineage-cell-Specific protein 1 (HS1) in freshly-isolated CLL cells or in CLL cells cultured with exogenous Wnt5a. Wnt5a also induced HS1 tyrosine phosphorylation, recruitment of ARHGEF1, activation of RhoA, and enhanced chemokine-directed migration; such effects could be inhibited by cirmtuzumab, a humanized anti-ROR1 mAb. We generated truncated forms of ROR1 and found its extra-cellular cysteine-rich domain or kringle domain was necessary for Wnt5a-induced HS1 phosphorylation. Moreover, the cytoplamic, and more specifically the proline-rich domain (PRD), of ROR1 was required for it to associate with HS1 and allow for F-actin polymerization in response to Wnt5a. Accordingly, we introduced single amino-acid substitutions of proline (P) to alanine (A) in the ROR1 PRD at positions 784, 808, 826, 841, or 850 in potential SH3-binding motifs. In contrast to wild-type ROR1, or other ROR1P⇒A mutants, ROR1P(841)A had impaired capacity to recruit HS1 and ARHGEF1 to ROR1 in response to Wnt5a. Moreover, Wnt5a could not induce cells expressing ROR1P(841)A to phosphorylate HS1 or activate ARHGEF1, and was unable to enhance CLL-cell motility. Collectively, these studies indicate HS1 plays an important role in ROR1-dependent Wnt5a-enhanced chemokine-directed leukemia-cell migration.Leukemia accepted article preview online, 03 May 2017. doi:10.1038/leu.2017.133.

https://www.ncbi.nlm.nih.gov/pubmed/28465529