2004 Global Researcher Conference Proceeding

April 09 - 11, 2004

Conference: 2004 Global Researcher Conference
Title: G15 reveals coupling of the V2 receptor to PLC that is refractory to receptor desensitization
Authors: Innamorati, Giulio; Piccirillo, Rosanna; Schiaffino, Maria Vittoria
Institutions: Vita Salute University School of Medicine, Scientific Institute San Raffaele

The V2 vasopressin receptor (V2R) couples to Gs and Gq/11 in the principal cells of the kidney. Among the mutations found in patients suffering of NDI is arginine 137 substituted to histidine (V2R-R137H). Contrary to many other mutations which cause NDI due to a loss of function of the receptor, this mutation determines constitutive activation of the V2R. However, the cell reacts to V2R hyperactivity by terminating receptor signaling. Analogous to what would occur to the wild type (WT) receptor occupied by AVP, phosphorylation and arrestin binding desensitize and internalize V2R-R137H.

V2R-R137H was expressed along with the WT receptor in COS cells to measure their ability to activate phospholipase C (PLC). Similar to what was observed for Gs coupling, while the stimulated WT receptor promoted IP3 accumulation, the V2R-R137H did not respond to saturating concentration of AVP and the level of intracellular IP3 remained at basal. As expected, V2R signaling to PLC was affected by arrestin binding. Supplementing the limited amount of native ß-arrestins present in COS cells, a 60% reduction of V2R-WT signaling to PLC was obtained by over-expression of either ß-arrestins isoforms.

G15 is another Gq/11 class member coupling a wide variety of receptors to PLC in co-transfected system. When G15 was over-expressed, the IP3 production stimulated by the V2R-WT was amplified, showing that the V2R can activate also this G-protein. Surprisingly, in a similar experiment, V2R-R137H coupling to G15 was found as functional as for the occupied WT receptor. Thus, it appears that G15 can circumvent receptor desensitization. This hypothesis was confirmed by experiments in which V2R-WT coupling to G15 resisted over-expression of ß-arrestins.

Gs and Gq/11 are members of the family of G proteins. V2R couples with Gs in the principal cells in the kidney collecting duct. Unlike most other V2R mutations, the mutant, V2R-R137H can be activated without binding to AVP. However, the principal cells react to this V2R-R137H hyperactivity by terminating its ability to send signals. The V2R-R137H then moves from the cell membrane to the cell interior.

Innamorati, et al., tested the ability of V2R-R137H to activate phospholipase C (PLC). They found that this mutant V2R could not activate PLC. The researchers also found that G15, a Gq/11 class member, can be activated by V2R. Surprisingly, V2R-R137H could also couple with G15. This indicates that G15 is able to couple with V2R-R137H despite the fact that V2R-R137H is desensitized by the cell.