Studies on protein kinases in two human rectocolic cell lines by polyacrylamide gel electrophoresis

Characterization of the vasoactive intestinal peptide (VIP) binding sites: a biochemical and an immunological approach

The initial event of VIP action is its interaction with a specific receptor at the surface of a target cell. The understanding of the fine mechanism of action of VIP requires the characterization and of course the purification of the receptor. The understanding of the mechanism which regulates the number of receptor sites at the cell surface, if it occurs, is also a way to characterize the properties of VIP receptor. In this paper we report a number of data which represent several attempts to characterize VIP receptor in a human colonic adenocarcinoma cell (HT 29 cells). We have characterized a monoclonal antibody which partially inhibits 125I-VIP binding to HT 29 cells. We have specifically cross-linked, on intact HT 29 cells, a major polypeptide of Mr-64,000 with 125I-VIP using DTSP or DSS as cross-linking reagents. This polypeptide behaves like a high affinity binding site for VIP. We have demonstrated that VIP is rapidly internalized in HT 29 cells (in less than 10 minutes) and that simultaneously VIP receptors were no more detectable on the cell surface by cross-linking experiments. This suggests that VIP is internalized together with its receptor.

Covalent cross-linking of vasoactive intestinal peptide (VIP) to its receptor in intact colonic adenocarcinoma cells in culture (HT 29)

[125I]Monoiodinated vasoactive intestinal peptide (125I-VIP) was cross-linked with human colonic adenocarcinoma cells (HT29 cells) grown as a monolayer using dithiobis(succinimidylpropionate) as cross-linking reagent. The cross-linked polypeptides were separated by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. A major polypeptide of Mr = 67 000 was characterized and it behaved like a high-affinity binding site for VIP according to the following data. The concentration of native VIP (0.5 nM) giving half-maximum inhibition of 125I-VIP covalent cross-linking with this polypeptide was very similar to that giving half-maximum displacement of 125I-VIP on HT 29 cells (0.6 nM). Glucagon or insulin was unable to inhibit the labelling of the Mr-67 000 component. In our experimental conditions neither specific 125I-VIP binding nor covalent labelling was observed with monolayers of Madin Darby canine kidney epithelial cells (MDCK cells) or African green monkey kidney fibroblasts (Vero cells) while the Mr-67 000 polypeptide was also characterized with human rectal adenocarcinoma cells (HRT 18 cells), known to possess the VIP receptor. Preincubation of HT 29 cells with native VIP at 37 degrees C, before 125I-VIP binding and subsequent cross-linking reaction, decreased the labelling of the Mr-67 000 polypeptide up to 80%. Assuming one molecule of 125I-VIP cross-linked per polypeptide, we have characterized, for the first time, a major polypeptide of Mr = 64 000, which belongs to the high-affinity VIP binding site of an intestinal human cell line.