Le. Heasley et al., HORMONAL-REGULATION OF MAP KINASE IN CULTURED RAT INNER MEDULLARY COLLECTING TUBULE CELLS, The American journal of physiology, 267(3), 1994, pp. 60000366-60000373
Mitogen-activated protein (MAP) kinase is a widely expressed protein s
erine/threonine kinase that serves as a convergence point for many sig
naling pathways including receptor tyrosine kinases, G protein-coupled
receptors, and protein kinase C (PKC). The hormonal regulation of MAP
kinase was studied in cultured established rat inner medullary collec
ting tubule (RIMCT) cells. Neither vasopressin nor beta-adrenergic ago
nists stimulated MAP kinase, despite clear stimulation of adenosine 3'
,5'-cyclic monophosphate (cAMP)-dependent protein kinase. In contrast,
carbachol, ATP, and epidermal growth factor (EGF), which are known to
antagonize vasopressin action in the RIMCT, stimulated the MAP kinase
pathway. This stimulation was mimicked by the phorbol ester, 12-O-tet
radecanoylphorbol-13-acetate, which directly activates PKC. The potenc
y with which EGF and carbachol activated MAP kinase was similar to the
potency with which they inhibited vasopressin-stimulated cAMP accumul
ation. To assess the role of G(i) proteins in these stimulatory events
, RIMCT cells were pretreated with pertussis toxin to inhibit G(i)-med
iated signaling. Pertussis toxin did not influence ATP- or EGF-stimula
ted MAP kinase, but completely inhibited carbachol stimulation, sugges
ting that G(i) proteins mediate muscarinic stimulation. Prolonged expo
sure of RIMCT cells to high phorbol ester concentrations to downregula
te PKC ablated carbachol- and ATP-stimulated MAP kinase, but not EGF-s
timulated MAP kinase, suggesting that PKC is a component of the networ
k involved in MAP kinase activation by purinergic and muscarinic agoni
sts. Investigation of the sidedness of the hormonal stimulations indic
ated that EGF-stimulated MAP kinase was highly polarized, occurring ex
clusively from the basolateral surface, whereas carbachol stimulated M
AP kinase similarly from either cell surface. Thus EGF, ATP, and carba
chol, three hormones that negatively influence vasopressin-stimulated
water transport in the collecting duct, signal MAP kinase activation t
hrough distinct mechanisms. The findings highlight the MAP kinases and
their upstream activators as a potential pathway, in addition to PKC,
involved in hormonal regulation of vasopressin action in the collecti
ng duct.