Regulation of CD45-induced signaling by galectin-1 in Burkitt lymphoma B cells

It has been well established that Galectin-1 (GAL1), a beta-galactoside-bin ding protein, regulates the viability of lymphoid cells. However, the signa ling pathway governed by the binding of GAL1 to the cell membrane is not un derstood. As a first step towards the elucidation of GAL1-initiated signali ng events leading to a reduced viability of Burkitt lymphoma B cells, we tr ied to characterize the initial events induced by the binding of GAL1 to it s receptor. This characterization was performed in BL36 cells, a Burkitt ly mphoma cell line sensitive to GAL1, The results were as follows: (1) when s olubilized cell membrane lysates were affinity bound to immobilized GAL1 an d eluted by competition, the tyrosine phosphatase glycoprotein CD45 was fou nd in the eluate, highlighting the role of CD45 as a receptor of GAL1; (2) the phosphatase activity of cell membranes diminished after incubation with GAL1; (3) immunoprecipitation experiments demonstrated that the phosphotyr osine kinase Lyn was dysregulated in cells that have been cultured in mediu m containing 700 nM GAL1, and (4) that the ratio between two isoforms of Ly n was modified during the treatment with GAL1. The regulation of Lyn theref ore seems to be a key event in the action of GAL1.