Differential expression and responsiveness of chemokine receptors (CXCR1–3) by human microvascular endothelial cells and umbilical vein endothelial cells

Abstract

The basis for the angiogenic effects of CXC chemokines such as interleukin 8 (IL-8) and for angiostatic chemokines such as interferon-inducible protein 10 (IP-10) has been difficult to assess. We recently reported, based on an RNase protection assay, that human umbilical vein endothelial cells (HUVECs) did not express detectable mRNA for the IL-8 receptors CXCR1 and CXCR2. This raised the possibility of heterogeneity of receptor expression by different endothelial cell (ECs) types. Since systemic angiogenesis induced by IL-8 would more likely involve microvessel ECs, we investigated CXC receptor expression on human microvascular dermal endothelial cells (HMECs). By confocal microscopy and immunofluorescence we observed that HMECs consistently expressed high levels of CXCR1 and CXCR4 (mean fluorescence intensity of 261+/-22.1 and 306.2+/-19, respectively) and intermediate levels of CXCR3 and CXCR2 (173.9+/-30. 2 and 156+/-30.9, respectively). In contrast, only a small proportion of HUVEC preparations expressed low levels of CXCR1, -2, and -3 (66+/-19.9; 49+/-15, and 81.4+/-17.9, respectively). However, both HMECs and HUVECs expressed equal levels of CXCR4. As expected, HMECs had more potent chemotactic responses to IL-8 than HUVECs, and this was correlated with the levels of IL-8 receptors on the ECs. Antibodies to CXCR1 and CXCR2 each had inhibitory effects on chemotaxis of HMECs to IL-8, indicating that both IL-8 receptors contributed to the migratory response of these cells toward IL-8. Assessment of the functional capacity of CXCR3 unexpectedly revealed that HMECs migrated in response to relatively higher concentrations (100-500 ng/ml) of each of the 'angiostatic' chemokines IP-10, ITAC, and MIG. Despite this, the 'angiostatic' chemokines inhibited the chemotactic response of HMECs to IL-8. IL-8 and SDF-1alpha but not IP-10 induced calcium mobilization in adherent ECs, suggesting that signaling events associated with calcium mobilization are separable from those required for chemotaxis. Taken together, our data indicated that functional differences among EC types is dependent on the level of the expression of CXC chemokine receptors. Whether this heterogeneity in receptor expression by ECs reflects distinct differentiation pathways remains to be established.

Suppression of metastatic hemangiosarcoma by a parvovirus MVMp vector transducing the IP-10 chemokine into immunocompetent mice

“…This possibility is raised by the recently reported capacity of human IP -10 for inhibiting endothelial cell growth, although the expression of the IP-10 receptor CXCR3 by normal and transformed endothelial cells is still a matter of controversy. 27,51,52 H5V cell cultures failed to express CXCR3 and were not sensitive to the MVMpmediated production of IP-10 (present work and Ref. [27 ]).…”

Interleukin-8/CXCL8 is a growth factor for human lung cancer cells

“…The role of each of these receptors in IL-8-mediated activity remains controversial. Previous studies have shown that the angiogenic effects of IL-8 in human microvascular endothelial cells and NSCLC were mediated by CXCR2 (Addison et al, 2000;Salcedo et al, 2000;Heidemann et al, 2003). The chemotactic response of melanoma cells to IL-8 was mediated by CXCR1 (Ramjeesingh et al, 2003), and the mitogenic activity of IL-8 was mediated by both CXCR1 and CXCR2 in colon cancer (Li et al, 2001), but only by CXCR1 in monocytes (Browning et al, 2000).…”

Transient inflammatory response induced by apoptotic cells is an important mediator of melanoma cell engraftment and growth

“…4 IL-8 is expressed in tumor cells and the IL-8 receptors CXCR1 and CXCR2, which are also receptors for the chemokines MIP-2 and GRO␣, are largely expressed in neutrophils. 47 Although expression of CXCR2 has also been reported in endothelial cells, 48,49 evidence has clearly shown that neutrophils are necessary mediators of the angiogenic response induced by CXCR2 agonists in vivo. 50 In wound-healing studies, angiogenesis begins immediately after injury and peaks after 7 days.…”