Engagement of CD44 modulates cyclooxygenase induction, VEGF generation, and cell proliferation in human vascular endothelial cells

Abstract

CD44 is a receptor for hyaluronic acid and is found on the surface of hematopoetic cells and in mesenchymal tissue. It is also expressed on endothelial cells (EC). Cyclooxygenase (COX) is the rate-limiting enzyme in the production of prostaglandins in EC. Here we show that engagement of CD44 with signaling monoclonal antibodies (mAbs) or its natural ligand hyaluronic acid induces COX-2 and prostacyclin (PGI 2 ) formation in human EC. This induction was blocked by mAbs that have been shown to inhibit CD44-mediated intracellular signaling. COX-1 induction was not observed after CD44 ligation. CD44-stimulated COX-2 activation/PGI 2 production was accompanied by the production of the potent endothelial mitogen, vascular endothelial growth factor (VEGF) and was inhibited by a neutralizing VEGF antibody. Moreover, this COX-2 induction was also associated with an increase in EC proliferation that was inhibited by the blocking anti-CD44 mAbs and a COX-2-specific inhibitor. This is the first study to show that engagement of CD44 with mAbs or its natural ligand induces COX-2, generates VEGF, and thus leads to an increase in EC proliferation. Results from this study may have important and widespread implications for the development of novel therapeutic agents for modulating blood vessel growth during ischemic heart disease, during inflammation, or around solid tumors.Key words: vascular endothelial growth factor • prostacyclin • COX he cell adhesion molecule CD44 is involved in a variety of important biological events such as embryogenesis, hematopoiesis, lymphocyte homing and activation, inflammatory reactions, and tumor dissemination (1-4). CD44 represents a large protein family, which includes the standard form or CD44 with a molecular mass of 85-90 kDa, and a multiplicity of isoforms generated by alternative splicing of transcripts and subsequent variable glycosylation (reviewed in ref 5). These high molecular mass variants are rarely expressed on normal cells. CD44 is the principal cell surface receptor for extracellular matrix glycosaminoglycan hyaluronan (HA). CD44-HA-mediated cell adhesion is important in several pathophysiological processes such as inflammation and metastatic spread of cancer cells. In this context, it has been recognized that CD44 can function as a signaling receptor in a variety of cell types (6). Cell stimulation by monoclonal anti-CD44 antibody or natural CD44 ligands activate signaling pathways that culminate in cell proliferation, cytokine secretion, chemokine gene expression, and cytolytic effector functions. Normal endothelial cells (EC) express low levels of CD44, but expression is up-regulated by activation with, for example, cytokines, and by culturing of these cells (7). Expression is also increased on the vasculature of solid tumors (7,8). Expression of CD44 on EC is associated with homing and migration of leukocytes (i.e., inflammation and migration). In addition, it has been demonstrated that CD44 plays some role in new blood vessel formation (angiogenesis), although its pre...

Low Molecular Weight Hyaluronan Activates Cytosolic Phospholipase A2α and Eicosanoid Production in Monocytes and Macrophages

“…These findings suggest that elevated HA levels in bronchoalveolar lavage and lung tissue in asthma or its local overproduction by tumor environment might stimulate monocyte-derived or tissue-resident macrophages to release AA and AA-derived eicosanoids through activation of cPLA 2 ␣. HA has been reported to increase PGE 2 production in human umbilical vein endothelial cells and in vivo in HA-treated mice, which was associated with simultaneous elevation of COX2 expression (76,77). Here, we showed that, even though COX2 expression was significantly increased in human monocytes and BMDM (Fig.…”

Involvement of Endothelial CD44 during in Vivo Angiogenesis

“…16 Our finding that the angiogenic response in the Matrigel assay was decreased in the CD44-null mice, led us to re-explore the effects of acute antibody inhibition by studying the activity of another well characterized anti-CD44 antibody, IM7.8.1. 22 The specificity of this antibody was confirmed by the fact it bound to wild-type but not CD44-null ECs (data not shown). IM7.8.1 inhibited the binding of murine ECs to HA ( Figure 7A) but had no effects on cell proliferation, migration, or susceptibility to apoptotic stress (Figure 7, B-D).…”

“…[15][16][17][18][19][20][21][22] Although there is evidence for the activity of RHAMM during in vivo angiogenesis, 16 the involvement of CD44 in the formation of blood vessels has not been estab-…”

OPN/CD44v6 overexpression in laryngeal dysplasia and correlation with clinical outcome

“…Addressing CD44 as a functional receptor for OPN would be important to explore the molecular mechanism underlying dysplastic changes induced by the OPN/CD44 axis. It is known that CD44 triggering stimulates diverse signalling pathways, including activation of ERK (Bourguignon et al, 2005), RAC (Teramoto et al, 2005), and RHO (Bourguignon et al, 2003), as well as secretion of soluble factors, like cytokines and metalloproteinases (Zhang et al, 2002;Bourguignon et al, 2003;Murphy et al, 2005). These pathways are potentially involved in dysplastic changes induced by OPN/CD44v6.…”