Identification of proteins that interact with Siglec-6

Siglec-6 is a glycoprotein overexpressed on chronic lymphocytic leukemia (CLL) cell. We have shown that Siglec-6 promotes migration and adhesion of CLL cells towards CLL bone marrow stromal cells. To elucidate the mechanistic pathway involved in Siglec-6 dependent migration, we performed mass spectrometry proteomics analysis on MEC1-002 CLL cell line pulled down with a Siglec-6 targeted antibody, which revealed that Siglec-6 interacts with DOCK8, a guanine nucleotide exchange factor. Interaction of Siglec-6 with its ligand promotes DOCK8 dependent Cdc42 activation, WASP protein recruitment and F-actin polymerization. Therapeutically, Siglec-6 leukemic cells can be eliminated with a Siglec-6 targeted bispecific antibody in vitro and in vivo.