Alpha‐1D‐Adrenoceptors Lacking Their Carboxyl Terminus Inhibit The MAPK/ERK Pathway in Rat‐1 Fibroblasts

Human alpha‐1D‐adrenoceptors are G protein‐coupled receptors that mediate the actions of adrenaline and noradrenaline participating in the maintenance of homeostasis as well as in the physiopathology of some diseases, such as hypertension and benign prostatic hyperplasia. There is a growing interest in investigating the function of their regulatory domains, such as the carboxyl tail. However, studies focused on the participation of this domain are limited. The objective of this work was to study the role of the human alpha‐1D‐adrenoceptor carboxyl tail in activation of the mitogen‐activated protein kinase pathway. To accomplish this, we assessed changes in extracellular signal‐regulated kinase (ERK) phosphorylation using biochemical and biophysical approaches. We found that Rat‐1 fibroblast expressing amino and carboxyl termini‐truncated (ΔNΔC) alpha‐1D‐adrenoceptor mutants were hardly able to activate the MAP kinase pathway in response to noradrenaline. Furthermore, expression of this mutant also decreased ERK activation induced by activation of other endogenous G protein‐coupled receptors and receptor tyrosine kinases, i. e., this mutant receptor alters downstream step(s) in the mitogen‐activated protein kinase pathway. As part of the mechanism, we showed that alpha‐1D‐adrenoceptor‐mediated ERK activation is PKC‐dependent. Moreover, we identified the inhibition of two key elements in the pathway downstream PKC: Raf‐1 and MEK1. In addition, we found that over‐expression of the alpha‐1D‐adrenoceptor third intracellular loop cannot mimic the effect of the carboxyl tail truncation, but is enough to activate ERK pathway. Our data indicate that both the alpha‐1D‐adrenoceptor carboxyl terminus and the third intracellular loop play roles in ERK signaling. Support or Funding Information This research was partially supported by Grants from PAPIIT‐DGAPA‐UNAM and CONACYT.