An Antibody to the Tetraspan Membrane Protein CD9 Promotes Neurite Formation in a Partially α3β1 Integrin-Dependent Manner

Abstract

The tetraspan cell surface glycoprotein, CD9, has been implicated in cellular signaling during growth and differentiation in the hematopoietic and nervous systems. Because CD9 expression is induced early in development in sensory and sympathetic neuroblasts, we investigated the role of CD9 in neurite outgrowth. We plated dissociated cells from neonatal sympathetic ganglia on immobilized anti-CD9 antibodies or antibodies against other cell surface molecules. We show here that B2C11, an anti-CD9 antibody that has been shown previously to activate Schwann cells in vitro, promotes robust neurite outgrowth from sympathetic neurons that is greater than that on other antibody surfaces and is comparable to neurite outgrowth on a collagen substratum. In addition, B2C11 causes dramatic morphological changes in neurons and glia from dissociated ganglia, including a flattening of these cells.Because CD9 interacts with integrins in many cell types including Schwann cells, and specifically with the ␣3␤1 integrin in some cells, we tested whether the effect of B2C11 on neurite outgrowth is mediated by this integrin. An anti-␣3␤1 antibody, Ralph 3-1, attenuates the extent of neurite outgrowth on B2C11 and collagen, but not on laminin. Because the ␣3␤1 integrin has been shown to mediate neurite outgrowth on different substrates, these results provide a functional significance for the CD9-␣3␤1 interaction; downstream signaling may be activated by this cis interaction on the cell surface in response to external cues that promote neurite outgrowth.

Absence of CD9 Enhances Adhesion-Dependent Morphologic Differentiation, Survival, and Matrix Metalloproteinase-2 Production in Small Cell Lung Cancer Cells

“…Anti-CD9 mAb increased neurite outgrowth in mouse cerebellar neurons (24). In addition, anti-CD9 mAb promoted neurite formation of rat sympathetic neurons in an integrin a 3 h 1 -dependent manner (25). Because CD9 + NCI-H446 morphologically differentiated as well as the CD9…”

Functional analysis of SIRPα in the growth cone

“…The substantial co-localization and co-fractionation of SIRP␣ and CD81 suggest that a large proportion of SIRP␣ and CD81 may reside together in LMDs that are physically and functionally distinct from 'standard rafts' and also contain adhesion molecules (Hemler, 2003). This is of particular interest in view of recent findings that critically implicate LMDs and tetraspanins (including CD81) in neurite outgrowth and turning (Schmidt et al, 1996;Banerjee et al, 1997;Stipp and Hemler, 2000;Guirland et al, 2004). It may suggest SIRP␣ involvement in growth control.…”

Functional Association of CD9 with the Fcγ Receptors in Macrophages

“…CD9 was reported to be associated with various integrin family molecules, CD5, CD19, and other TM4SF proteins on the cell surface and has been postulated to participate in the regulation of cell growth, motility, and signaling (8 -16). Besides monocytes/ macrophages, CD9 is expressed on certain hematopoietic lineage cells such as platelets, subpopulations of lymphocytes, eosinophils, and basophils and on some other cell lineages such as endothelial cells, myoblasts, and neuroblasts (8,15,16). Additionally, CD9 is expressed in oocytes, and CD9-deficient female mice showed serious sterility caused by a defect in the gamete fusion process (17)(18)(19)(20).…”