REGULATED EXPRESSION OF A 16-KD GALECTIN-LIKE PROTEIN IN ACTIVATED RAT MACROPHAGES

We investigated the presence of a galectin-like protein in rat mononuc lear cells using a polyclonal antibody raised against a soluble lactos e-binding lectin purified from adult chicken liver that immunoreacted strongly with a broad protein band of about 16 kd in Western blot assa ys, Immunochemical studies revealed a constitutive expression of this protein in mononuclear cells mainly in the macrophage (M phi) populati on, Subcellular localization was assessed by Western blot assays of th e cytosolic and membrane fractions of different cell populations studi ed: (1) spleen mononuclear cells, (2) T cell-enriched, (3) B cell- and M phi-enriched populations, and (4) peritoneal cells, processed in th e presence of lactose, In broad agreement with immunocytochemical stud ies of nonpermeabilized and permeabilized cells, Western blot assays s uggest that this protein is localized mainly in the cytoplasmic compar tment but also associated with the cell surface, By flow cytometric an alyses we detected about a 14% of ED1 double-positive cells correspond ing to M phi s that constitutively express this galectin-like protein associated with their cell surface, The cytosolic fraction obtained fr om the M phi-enriched cell population showed hemagglutinating activity specifically inhibited by beta-galactoside-related sugars. Moreover, this galectin-like protein was retained in a lactosyl-Sepharose matrix and specifically eluted with lactose, In this work, evidence is also provided to show that different stimuli are able to modulate the expre ssion of the galectin-like protein, Expression was upregulated in infl ammatory and activated M phi s, revealing a significant increase in ph orbol ester- and formylmethionine oligopeptide-treated cells, Both sti muli involving protein kinase C activation pathway have been able not only to up-regulate the total expression of this protein but also to m odulate its subcellular localization.