Variations in the cytoskeletal interaction and posttranslational modification of the CD44 homing receptor in macrophages.

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Abstract
Murine CD44 is a cell surface glycoprotein that is thought to play a role in leukocyte migration. We studied the structure and expression of CD44 on two populations of macrophages: those that reside in the peritoneum of unprimed mice, and those that have been elicited to migrate into the peritoneum by the intraperitoneal injection of agents that cause localized inflammatory responses. Our studies reveal structural variations in both the extracellular and intracellular domains of CD44 expressed by these two macrophage populations. The form of CD44 in elicited macrophages has an apparent molecular mass that is approximately 5 kD greater and more heterogenous than that in resident macrophages. This structural changes is posttranslational, extracellular, and apparently reflects increases in N-linked glycosylation. It is also specific for CD44 and does not occur with several other glycoproteins examined. This novel regulation of glycosylation may play an important role in the ability of CD44 to bind to different substrates, particularly lectin-like ligands. In addition, we demonstrate that CD44 in resident macrophages is divided into two pools, one containing nonphosphorylated, cytoskeletally associated CD44, and one containing phosphorylated, unassociated CD44. In contrast, CD44 on the surface of elicited macrophages does not associate with the cytoskeleton. The attachment of CD44 to the cytoskeleton involves either direct or indirect association with actin. The regulated association of CD44 with the cytoskeleton suggests that it may influence or be influenced by macrophage mobility.