Abstract 1542: CD38 is physically associated with CD49d and enhances CD49d-mediated adhesion of B-Cell chronic lymphocytic leukemia cells

Abstract

Abstract CD49d, a recently identified negative prognosticator in chronic lymphocytic leukemia (CLL), is an adhesion molecule mediating microenvironmental interactions of CLL cells in bone marrow and lymph nodes. Through CD49d-dependent adhesion to VCAM-1 and fibronectin (FN), CLL cells receive survival support that renders them less susceptible to conventional therapies. The closely associated expression of CD49d with CD38, another negative prognosticator in CLL, and the propensity of CD38 to associate and functionally cooperate with other molecules, prompted us to investigate whether: i) CD38/CD49d physical interactions may also occur on CLL cell membranes; ii) CD38 may potentiate the CD49d-mediated adhesion in CLL. Confocal microscopy and biochemical approaches were used to study the membrane organization of CD49d and CD38 in CLL cells. The CLL-derived CD49d+CD38- cell line Mec-1, and a subclone in which CD38 expression was induced by viral transduction (Mec-1/CD38) were utilized for adhesion experiments. Co-capping experiments in CD49d+/CD38+ CLL cells demonstrated a membrane relationship between CD38 and CD49d. Anti-CD49d monoclonal antibodies (mAbs) induced capping in approximately 75% of CLL cells, with a 80% redistribution of CD38 in the context of the capping area. The CD38/CD49d lateral association was confirmed by immunoprecipitation experiments with anti-CD49d mAbs and subsequent painting of immunoprecipitates using anti-CD38 mAbs. CD38/CD49d association was also maintained after engagement of CD49d with its natural ligands, as witnessed by co-localization of CD49d and CD38 in uropods of CLL cells adhered and spread onto VCAM-1 and FN. To investigate whether the CD38/CD49d association had also a functional meaning, adhesion assays on VCAM-1-coated plates were performed with the Mec-1 cell model. Mec-1/CD38 showed a marked increase in VCAM-1 adhesion compared to Mec-1 (mean values of adhered cells relative to control=5.4 vs. 2.3 and 5.4 vs. 1.9 after 15 and 30 minutes, respectively; p=0.01). Moreover, phase-contrast and immunofluorescence microscopy highlighted clear differences in the morphology of adhered cells, with Mec-1/CD38 cells characterized by a more complex pattern of uropods than Mec-1, and a clear co-localization of CD38 and CD49d in adhesion sites. Notably adhesion of Mec-1/CD38 cells to VCAM-1 resulted in higher levels of phosphorylation of the guanidine nucleotide exchange factor for Rho proteins Vav-1 and, subsequently, of higher F-actin polymerization, as compared to non transfected Mec-1 cells. CD49d and CD38 are physically associated on CLL cells membranes. CD38 directly contributes in enhancing CD49d-dependent adhesion to VCAM-1. Post-translationally modified proteins involved in CD49d-mediated cell adhesion will be quantified on CD49d-expressing CLL cells with different CD38 levels using Reverse Phase Microarray technology. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1542. doi:10.1158/1538-7445.AM2011-1542