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The role of the kinase insert domain-containing receptor (KDR) in the Ca2+ mobilization in human umbilical vein endothelial cells (HUVEC) was determined by preparing a polyclonal mouse antibody against the first three immunoglobulin-like domains of KDR. The serum was found to inhibit vascular endothelial cell growth factor (VEGF165) binding to the KDR and signaling through Ca2+ in HUVEC. The inhibition of KDR plus the lack of response to placental growth factor suggests that the binding of VEGF165 to KDR does not translate into a Ca2+ response.

The structure of the alpha-subunit of bovine kidney epithelial Na+ channel (alpha-bENaC) obtained from the renal collecting duct is 75-85% similar to the rat and human homolog. Alpha-bENaC has an open-reading frame which produces a protein containing 697 amino acids. The expression of alpha-bENaC in Xenopus oocytes causes a Na+ current which is unaffected by an increase in the concentration of adenosine 3,5'-cyclic monophosphate but increases if protein kinase C is stimulated. The cloning and amino acid sequence of alpha-bENaC cDNA is given.

We have previously reported that junctional adhesion molecule 2 (JAM2) adheres to T cells through heterotypic interactions with JAM3. An examination of the cation dependence of JAM2 adhesion to HSB cells revealed a Mn(2+)-enhanced binding component indicative of integrin involvement. Using neutralizing integrin antibodies, we have defined an interaction between JAM2 and alpha(4)beta(1) in T cells. The interaction is readily amenable to drug intervention as demonstrated by the ability of TBC 772, an alpha(4)-specific inhibitor, to attenuate the Mn(2+)-enhanced component. Intriguingly, the engagement of alpha(4)beta(1) by JAM2 is only enabled following prior adhesion of JAM2 with JAM3 and is not detectable in cells where JAM3 expression is absent. Supporting this observation, we show that neutralizing JAM3 serum and soluble JAM3 ectodomain inhibit not only JAM2 binding to JAM3 but also prevent JAM2/alpha(4)beta(1) interactions in T cells. We further define the first Ig-like fold of JAM2 as being competent in binding both JAM3 and alpha(4)beta(1) counter-receptors. Mutagenesis of the only acidic residue in the C-D loop of this Ig fold, namely Asp-82, has no bearing on alpha(4)beta(1) interactions, and thus JAM2 deviates somewhat from the mechanism used by other immunoglobulin superfamily cell adhesion molecules to engage integrin.