PT  - JOURNAL ARTICLE
AU  - Turner, J T
AU  - Bollinger, D W
AU  - Toews, M L
TI  - Vasoactive intestinal peptide receptor/adenylate cyclase system: differences between agonist- and protein kinase C-mediated desensitization and further evidence for receptor internalization.
DP  - 1988 Nov 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 417--423
VI  - 247
IP  - 2
4099  - http://jpet.aspetjournals.org/content/247/2/417.short
4100  - http://jpet.aspetjournals.org/content/247/2/417.full
SO  - J Pharmacol Exp Ther1988 Nov 01; 247
AB  - In this study we have characterized and compared the regulation of the HT29 cell vasoactive intestinal peptide receptor/adenylate cyclase system (VIP-R/AC) by the VIP-R agonist peptide histidineisoleucineamide (PHI) and by activators of protein kinase C (PKC) including phorbol 12-myristate, 13-acetate (PMA) and mezerein. Preincubation with either PHI or PKC activator decreased maximum VIP-stimulated AC activity and decreased the number of cell surface VIP-R. A [125I]VIP binding assay using solubilized VIP-R of the plasma membrane and light vesicle fractions from sucrose density step gradients was developed as a more direct measure of VIP-R internalization. Preincubation with PHI or PMA decreased plasma membrane fraction [125I]VIP binding and increased binding in the light vesicle fraction, thus providing the most direct evidence to date for translocation of VIP-R per se from the plasma membrane to another, presumably intracellular, compartment. Two experimental approaches differentiated between agonist and PKC activator regulation of VIP-R/AC. The protein kinase inhibitors H-7 and staurosporine blocked mezerein-, but not PHI-, induced losses of cell surface VIP-R. Also, down-regulation of PKC did not block PHI-induced loss of cell surface VIP-R. Thus, although both agonist and PKC activators can lead to desensitization and internalization of VIP-R, PKC is apparently not involved in the mechanisms of agonist-induced desensitization.