1 and markedly augments VCAM-1 expression induced by TNF or IL-1 (1-6). These changes favor the binding of eosinophils and T cells to endothelial cells (ECs). In addition, IL-4-treated ECs secrete the chemokine MCP-1 (7) and selectively stimulate transendothelial migration of eosinophils in vitro (8). The effects of IL-4 on EC differ from those on hematopoietic cell types in that IL-4 is not an endothelial mitogen or survival factor.IL-13 is another pleiotropic immunoregulatory cytokine (9, 10) that shares a number of biological properties with IL-4 (11-16). IL-13, like IL-4, selectively induces VCAM-1 in cultured human ECs (17, 18). IL-13 has been shown recently to stimulate tyrosine phosphorylation of the IL-4-binding subunit of the 140-kD IL-4 receptor (IL-4R) in a number of hematopoietic cell types (19), suggesting that IL-4 and IL-13 may activate a common tyrosine kinase. Two recent findings further suggest that the IL-13-binding subunit of the IL-13 receptor (IL-13R) may share at least one subunit with the IL-4R: ( a ) the IL-4 mutant protein Y124D, which inhibits IL-4-dependent reactions (20) also inhibits effects of IL-13 (21, 22); and ( b ) IL-13 competes with radiolabeled IL-4 for binding to some cells (21-24).The IL-2 receptor (IL-2R) ␥ chain is a functional component of the IL-4R in lymphocytes, required for tyrosine phosphorylation of the insulin receptor substrate-1 in response to IL-4 (25) and for IL-4-induced cell proliferation (26). The (IL-2R) ␥ chain, recently renamed the common ␥ chain ( ␥ c chain), is also a common receptor component of many other members of the cytokine receptor superfamily including , [30][31][32]34). It is not known if IL-13 can signal through ␥ c , but some cell lines of hematopoietic origin are known to respond to IL-4 and IL-13 in the absence of ␥ c (24,35). This evidence suggests two distinct signaling pathways for IL-4, one involving ␥ c , and an alternate pathway, shared with IL-13, that does not use ␥ c .Previous work by our laboratory has shown that IL-4 activates a protein tyrosine kinase that phosphorylates the IL-4R binding subunit in cultured human ECs and that activation of this protein tyrosine kinase may play a part in the signaling pathway leading to increased VCAM-1 expression in response to . We now show that IL-13, like IL-4, causes the activation of a protein tyrosine kinase in ECs that phosphorylates IL-4R, that both cytokines activate JAK2 and the Stat6 transcription factor, and that these responses cannot involve ␥ c , since this protein is not expressed in ECs.
MethodsCell isolation and culture. ECs were isolated and cultured as described previously (37,38). ECs used in these experiments were of passage levels 2 to 5 and were free of detectable CD45 ϩ leukocytes. PHA- 1. Abbreviations used in this paper: EC, endothelial cell; JAK, Janus kinase; RT, reverse transcription; Stat, signal transducer and activator of transcription; VCAM-1, vascular cell adhesion molecule-1.