Lysophosphatidic Acid Stimulates Brush Border Na+/H+ Exchanger 3 (NHE3) Activity by Increasing Its Exocytosis by an NHE3 Kinase A Regulatory Protein-dependent Mechanism

Abstract

Na+/H+exchanger 3 (NHE3) kinase A regulatory protein (E3KARP) has been implicated in cAMP- and Ca2+-dependent inhibition of NHE3. In the current study, a new role of E3KARP is demonstrated in the stimulation of NHE3 activity. Lysophosphatidic acid (LPA) is a mediator of the restitution phase of inflammation but has not been studied for effects on sodium absorption. LPA has no effect on NHE3 activity in opossum kidney (OK) proximal tubule cells, which lack expression of endogenous E3KARP. However, in OK cells exogenously expressing E3KARP, LPA stimulated NHE3 activity. Consistent with the stimulatory effect on NHE3 activity, LPA treatment increased the surface NHE3 amount, which occurred by accelerating exocytic trafficking (endocytic recycling) to the apical plasma membrane. These LPA effects only occurred in OK cells transfected with E3KARP. The LPA-induced increases of NHE3 activity, surface NHE3 amounts, and exocytosis were completely inhibited by pretreatment with the PI 3-kinase inhibitor, LY294002. LPA stimulation of the phosphorylation of Akt was used as an assay for PI 3-kinase activity. LY294002 completely prevented the LPA-induced increase in Akt phosphorylation, which is consistent with the inhibitory effect of LY294002 on the LPA stimulation of NHE3 activity. The LPA-induced phosphorylation of Akt was the same in OK cells with and without E3KARP. These results show that LPA stimulates NHE3 in the apical surface of OK cells by a mechanism that is dependent on both E3KARP and PI 3-kinase. This is the first demonstration that rapid stimulation of NHE3 activity is dependent on an apical membrane PDZ domain protein. Na+/H+exchanger 3 (NHE3) kinase A regulatory protein (E3KARP) has been implicated in cAMP- and Ca2+-dependent inhibition of NHE3. In the current study, a new role of E3KARP is demonstrated in the stimulation of NHE3 activity. Lysophosphatidic acid (LPA) is a mediator of the restitution phase of inflammation but has not been studied for effects on sodium absorption. LPA has no effect on NHE3 activity in opossum kidney (OK) proximal tubule cells, which lack expression of endogenous E3KARP. However, in OK cells exogenously expressing E3KARP, LPA stimulated NHE3 activity. Consistent with the stimulatory effect on NHE3 activity, LPA treatment increased the surface NHE3 amount, which occurred by accelerating exocytic trafficking (endocytic recycling) to the apical plasma membrane. These LPA effects only occurred in OK cells transfected with E3KARP. The LPA-induced increases of NHE3 activity, surface NHE3 amounts, and exocytosis were completely inhibited by pretreatment with the PI 3-kinase inhibitor, LY294002. LPA stimulation of the phosphorylation of Akt was used as an assay for PI 3-kinase activity. LY294002 completely prevented the LPA-induced increase in Akt phosphorylation, which is consistent with the inhibitory effect of LY294002 on the LPA stimulation of NHE3 activity. The LPA-induced phosphorylation of Akt was the same in OK cells with and without E3KARP. These results show that LPA stimulates NHE3 in the apical surface of OK cells by a mechanism that is dependent on both E3KARP and PI 3-kinase. This is the first demonstration that rapid stimulation of NHE3 activity is dependent on an apical membrane PDZ domain protein. Na+/H+ exchanger 3 Na+/H+ exchanger regulatory factor NHE3 kinase A regulatory protein phosphatidylinositol lysophosphatidic acid acetoxymethyl ester of 2′7′-bis(carboxyethyl)5–6-carboxyfluorescein phosphate-buffered saline brush border opossum kidney extracellular signal-regulated kinase vesicular stomatitis virus G-protein Na+/H+ exchanger 3 (NHE3)1 plays an essential role in NaCl and NaHCO3 absorption in ileum, colon, gallbladder, and proximal tubule of kidney (1Donowitz M. Tse M. Barrett K.E. Donowitz M. Gastrointestinal Transport Molecular Physiology: Current Topics in Membranes. 50. Academic Press, San Diego2000: 437-498Google Scholar, 2Brett C.L. Wei Y. Donowitz M. Rao R. Am. J. Physiol. 2002; 282: C1031-C1041Crossref PubMed Scopus (147) Google Scholar, 3Numata M. Orlowski J. J. Biol. Chem. 2001; 276: 17387-17394Abstract Full Text Full Text PDF PubMed Scopus (218) Google Scholar). NHE3 cycles between the plasma membrane and recycling endosomal compartment under basal conditions (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 5Donowitz M. Janecki A. Akhter S. Cavet M.E. Sanchez F. Lamprecht G. Khurana S. Yun C.H.C. Ann. N. Y. Acad. Sci. 2000; 915: 30-42Crossref PubMed Scopus (45) Google Scholar, 6Lee-Kwon W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 7Akhter S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, 8Kurashima K. Szabo E.Z. Lukacs G. Orlowski J. Grinstein S. J. Biol. Chem. 1998; 273: 20828-20836Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar, 9D'Souza S. Garcia-Cabado A., Yu, F. Teter K. Lukacs G. Skorecki K. Orlowski J. Grinstein S. J. Biol. Chem. 1998; 273: 2035-2043Abstract Full Text Full Text PDF PubMed Scopus (204) Google Scholar). NHE3 is both rapidly stimulated and inhibited by several growth factors, neurotransmitters, and hormones that are released as part of digestion (1Donowitz M. Tse M. Barrett K.E. Donowitz M. Gastrointestinal Transport Molecular Physiology: Current Topics in Membranes. 50. Academic Press, San Diego2000: 437-498Google Scholar). These act by altering the amount of the NHE3 in the plasma membrane, as well as by changes in the NHE3 turnover number (1Donowitz M. Tse M. Barrett K.E. Donowitz M. Gastrointestinal Transport Molecular Physiology: Current Topics in Membranes. 50. Academic Press, San Diego2000: 437-498Google Scholar). For instance, growth factor and sodium absorption by the of NHE3 in the brush border X. S. G. A. Donowitz M. J. Physiol. 2001; PubMed Scopus Google Scholar). In transfected with the surface NHE3 are stimulated by treatment with growth factor (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar). In opossum kidney proximal tubule cells exogenously transfected with the treatment with increased the surface NHE3 amount and NHE3 activity K. J. 2001; PubMed Scopus Google Scholar, Y. M. X. M. Am. J. Physiol. 2001; PubMed Google by an increase in of surface NHE3 is a mechanism in the stimulation of NHE3 activity by growth and 3-kinase has been implicated in stimulation of several plasma membrane of and NHE3 (1Donowitz M. Tse M. Barrett K.E. Donowitz M. Gastrointestinal Transport Molecular Physiology: Current Topics in Membranes. 50. Academic Press, San Diego2000: 437-498Google Scholar, A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 5Donowitz M. Janecki A. Akhter S. Cavet M.E. Sanchez F. Lamprecht G. Khurana S. Yun C.H.C. Ann. N. Y. Acad. Sci. 2000; 915: 30-42Crossref PubMed Scopus (45) Google Scholar, 6Lee-Kwon W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 7Akhter S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, 8Kurashima K. Szabo E.Z. Lukacs G. Orlowski J. Grinstein S. J. Biol. Chem. 1998; 273: 20828-20836Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar, 9D'Souza S. Garcia-Cabado A., Yu, F. Teter K. Lukacs G. Skorecki K. Orlowski J. Grinstein S. J. Biol. Chem. 1998; 273: 2035-2043Abstract Full Text Full Text PDF PubMed Scopus (204) Google Scholar, S. Chem. Full Text Full Text PDF Scopus Google Scholar, 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus (204) Google Scholar). PI 3-kinase is with of to the plasma membrane. of PI 3-kinase results in increased of and of the of the protein kinase Akt W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, Li Y. PubMed Google Scholar). PI 3-kinase and Akt are in the to plasma and a Akt stimulates S. Chem. Full Text Full Text PDF Scopus Google Scholar, Li A. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). PI 3-kinase the basal and stimulated of plasma membrane NHE3 amount and NHE3 activity. In and OK cells, basal NHE3 activity and surface amount are by by the PI 3-kinase and LY294002 (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 7Akhter S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar). the growth growth increase of NHE3 activity in cells, and is inhibited by PI 3-kinase (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, S. Tse M.E. Donowitz M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Consistent with W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google that of PI 3-kinase and Akt stimulated NHE3 activity in by the NHE3 amount in the plasma membrane, and a of PI 3-kinase the same effect in OK cells W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar). These results that PI 3-kinase and Akt which is stimulated by PI and in the stimulation of exocytosis of NHE3 in and E3KARP, which are PDZ and an domain C.H.C. S. M. S. Tse Donowitz M. Acad. Sci. S. A. PubMed Scopus Google Scholar). been implicated in inhibition of NHE3 activity C.H.C. S. M. S. Tse Donowitz M. Acad. Sci. S. A. PubMed Scopus Google only E3KARP is in dependent inhibition of NHE3 W. Park Yun Donowitz M. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). These PDZ domain with NHE3 PDZ and with which to the and as an protein for protein kinase Lamprecht A. J. Biol. Chem. 1998; 273: Full Text Full Text PDF PubMed Scopus Google Scholar). both and E3KARP NHE3 to protein kinase for the inhibition of NHE3 activity protein kinase The protein kinase phosphorylation of NHE3 is for of NHE3 M. Lamprecht G. N. S. Donowitz M. Yun C.H.C. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). has not been studied PDZ domain are in rapid stimulation of NHE3 activity and in the recycling of NHE3 to the plasma membrane. Lysophosphatidic acid (LPA) is an mediator Y. K.E. 2002; PubMed Scopus Google Scholar, 2002; PubMed Scopus Google Scholar, K. N. G. 2002; PubMed Scopus Google Scholar, O. Biol. PubMed Scopus Google Scholar). is a released by and LPA is released in the of in the and proximal LPA restitution and A. A. Ann. N. Y. Acad. Sci. 1998; PubMed Scopus Google Scholar, A. Full Text Full Text PDF PubMed Scopus Google Scholar, N. J. J. 2000; Full Text PDF PubMed Scopus Google Scholar). In opossum kidney proximal tubule cells, LPA on a the of PI 3-kinase and the extracellular signal-regulated kinase Full Text Full Text PDF PubMed Scopus Google Scholar). In study, the first that LPA stimulates sodium by NHE3 activity and the amount of NHE3 on the plasma membrane. This by stimulation of exocytic trafficking by of PI 3-kinase. E3KARP but not is for LPA-induced stimulation of NHE3 activity and increase of NHE3 in the plasma membrane. This is the demonstration of E3KARP in rapid stimulation of sodium absorption. on the with the vesicular stomatitis virus G-protein cells by J. of as S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, Tse Donowitz M. J. Biol. Chem. Full Text PDF PubMed Google were in with sodium and in a were for Na+/H+ exchanger activity by cells to an acid of NaCl for by an as Tse Donowitz M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). A of expressing E3KARP was by of cells with a E3KARP. was with as S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google and cells were in growth to the to the were to Na+/H+ activity in OK was the acetoxymethyl ester of Molecular as S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, Tse Donowitz M. J. Biol. Chem. Full Text PDF PubMed Google Scholar). OK cells were on and were in for was studied K. J. 2001; PubMed Scopus Google Scholar, Y. M. X. M. Am. J. Physiol. 2001; PubMed Google Scholar). For and cells were in and for were with which was to for the the of the was to the to and Na+/H+ activity were as the of changes in the were by to and M.E. Akhter S. Sanchez F. Donowitz M. Tse Am. J. Physiol. PubMed Google Scholar). In Na+/H+ activity was as the of a of as by The of NHE3 on the plasma membrane were by of surface as S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, M.E. Akhter S. Sanchez F. Donowitz M. Tse Am. J. Physiol. PubMed Google Scholar). OK cells as were for and to LPA for the were were with phosphate-buffered saline and in and were to in for with cells were with to the were with phosphate-buffered saline and in of 3 3 and by for was by for the NHE3 was with for and the were in to The to which surface were with The and surface were by and to membrane. with the were with a as the and as the and were by O. Yun M.E. A.J. Tse Donowitz M. Am. J. Physiol. Google Scholar). The of NHE3 protein were by and was by a the assay by W. Park Yun Donowitz M. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). were with for and were to with J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google for and with phosphate-buffered saline was by with The were with were in and were and for NHE3 as exocytic of on the surface were first by pretreatment with as with Y. M. X. M. Am. J. Physiol. 2001; PubMed Google Scholar, J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). were with phosphate-buffered saline with and The apical surface was to in for for cells were with and with LPA for were with and with The which surface was by and the was to and with as the E3KARP is in stimulation of an OK expressing both and E3KARP as under The expression of and E3KARP in the were in E3KARP is in cells but not in OK is in OK cells in The of E3KARP expression is in cells in the cells W. Park Yun Donowitz M. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). is in cells, in to the expression of endogenous in cells W. S. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). factors, growth factor and growth increase NHE3 activity in cells and in and stimulates NHE3 in OK cells (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 7Akhter S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar, K. J. 2001; PubMed Scopus Google Scholar, Y. M. X. M. Am. J. Physiol. 2001; PubMed Google Scholar). as an of the of the restitution phase of NHE3 activity in proximal tubule cells, and cells with LPA for and NHE3 activity. in LPA treatment increase in cells, in In NHE3 activity was not by LPA treatment in cells The and of the LPA-induced stimulation of NHE3 activity were in LPA increased NHE3 activity as as and the increased to LPA NHE3 in a to with no effect This of LPA on NHE3 activity is to the of LPA on of OK cells Full Text Full Text PDF PubMed Scopus Google Scholar). These results show that LPA stimulates NHE3 activity by an and effects of LPA on NHE3 cells were with LPA for the and the of was cells were with the of LPA for For of were the by a of the LPA-induced increase of NHE3 activity was of an increase of amount of plasma membrane NHE3 the surface NHE3 by surface membrane were by with and were by with in treatment with LPA for not the surface of NHE3 in cells In in cells, LPA treatment an increase in apical membrane NHE3 protein in a consistent with the stimulation of NHE3 activity by LPA treatment in of LPA increased the amount of surface NHE3. The LPA-induced increase in the surface NHE3 amount occurred without in NHE3 These results that the LPA-induced of NHE3 is of the increase of the amount of surface NHE3. The increase in surface NHE3 amount of a in an increase in exocytic of NHE3. which mechanism was in the increase of surface NHE3 amount, the of and exocytosis of NHE3 in cells were the exocytic plasma membrane were by pretreatment with Y. M. X. M. Am. J. Physiol. 2001; PubMed Google Scholar). were with LPA for by of surface NHE3 NHE3 that was in and on the plasma membrane treatment with treatment with LPA for of NHE3 were increased in cells LPA increased the NHE3 exocytic trafficking by on These results that exocytic trafficking of NHE3 for the LPA-induced increase of surface NHE3 amount with of LPA the of apical membrane were with treatment with LPA for cells were to which surface NHE3 the of NHE3 that was on the apical membrane and was Consistent with a J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google was increased NHE3 plasma membrane treatment with for In LPA treatment for no effect on the amount of NHE3 and on These results that of NHE3 is not in the LPA-induced increase of surface NHE3 PI 3-kinase has been implicated in basal and stimulated of NHE3 activity in and cells and basal NHE3 activity in OK cells on of PI and and stimulation of PI 3-kinase (4Janecki A.J. Janecki M. Akhter S. Donowitz M. J. Biol. Chem. 2000; 275: 8133-8142Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar, 5Donowitz M. Janecki A. Akhter S. Cavet M.E. Sanchez F. Lamprecht G. Khurana S. Yun C.H.C. Ann. N. Y. Acad. Sci. 2000; 915: 30-42Crossref PubMed Scopus (45) Google Scholar, 6Lee-Kwon W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google Scholar, 7Akhter S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar). W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google that of PI 3-kinase and Akt stimulated basal NHE3 activity by surface NHE3 in PI 3-kinase and Akt were in the LPA-induced of the effect of the PI 3-kinase inhibitor, on the LPA-induced NHE3 in in pretreatment with inhibited basal NHE3 activity by which is consistent with in OK cells S. Kovbasnjuk O. Li X. Cavet M. Noel J. Arpin M. Hubbard A. Donowitz M. Am. J. Physiol. 2002; 283: C927-C940Crossref PubMed Scopus (60) Google Scholar). In LY294002 pretreatment completely the LPA-induced stimulation of NHE3 activity. These results that PI 3-kinase is for the LPA-induced stimulation of as well as in basal NHE3 activity. LPA stimulates the NHE3 activity the of NHE3 on the apical plasma membrane in cells the increase of surface NHE3 the of PI the effect of LY294002 on the surface NHE3 in in the of NHE3 on the plasma membrane were increased by LPA LY294002 pretreatment completely the LPA-induced increase of surface NHE3 LY294002 a but in basal surface NHE3 These changes in surface NHE3 the inhibitory effect of LY294002 on the as well as NHE3 activity. The LPA-induced increase of surface NHE3 amount is of exocytic trafficking of NHE3 to the apical plasma membrane A and the effect of LY294002 pretreatment on the LPA-induced increase of exocytic trafficking of NHE3. in the LPA-induced increase of exocytic trafficking was completely prevented by pretreatment with LY294002. This that PI 3-kinase plays a role in the increase of NHE3 exocytosis to the apical plasma membrane. In LY294002 pretreatment the basal of exocytic trafficking of NHE3 in the of LPA The mechanism of the E3KARP of LPA stimulation of NHE3 is not The was that E3KARP increased the LPA stimulation of PI 3-kinase as the mechanism by which E3KARP to LPA stimulation of NHE3. The assay used for PI 3-kinase activity was of Akt as as amount of the phosphorylation of Akt treatment with LPA in both and cells by for which and for Akt in in both and cells, Akt was by of LPA with phosphorylation The Akt phosphorylation was to the of stimulation of Akt phosphorylation to basal Akt and the of basal Akt phosphorylation were in and The LPA-induced phosphorylation of Akt was prevented by pretreatment with consistent with the inhibitory effect of LY294002 on NHE3 activity and the exocytic trafficking of NHE3. PI 3-kinase activity is for the LPA-induced stimulation of NHE3 activity and exocytic trafficking of results show that PI not E3KARP is for LPA stimulation of NHE3. has been implicated in growth of and in NHE3 J. Grinstein S. J. Biol. 2001; PubMed Scopus Google Scholar, G. J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In OK cells, of as well as of PI has been Full Text Full Text PDF PubMed Scopus Google Scholar). is in the LPA-induced NHE3 the effect of a of on the of NHE3 in in basal NHE3 activity and the NHE3 were not by pretreatment with that the LPA-induced phosphorylation is not by LY294002 treatment not These results show that the LPA-induced phosphorylation is by a mechanism that is not PI 3-kinase LPA of is not in LPA stimulation of NHE3. LPA in OK cells, only of which are in NHE3 and PI 3-kinase In LPA was to NHE3 activity and to increase the of NHE3 on the plasma membrane by exocytic These were dependent on the of E3KARP. of NHE3 that by E3KARP C.H.C. S. M. S. Tse Donowitz M. Acad. Sci. S. A. PubMed Scopus Google the LPA stimulation of NHE3 activity only occurred in the of E3KARP and not This in an effect of E3KARP has only been W. Park Yun Donowitz M. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google for inhibition of kinase stimulation of NHE3 Y. F. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google and of Donowitz M. 2001; PubMed Scopus Google Scholar). The Ca2+-dependent inhibition of NHE3 was of of E3KARP but not with the protein In E3KARP with and to for the E3KARP In and E3KARP both inhibition of both which protein kinase to the PDZ domain is that the of E3KARP to of of a protein in LPA that is for NHE3 the for the E3KARP of the LPA-induced NHE3 has not been These show that E3KARP is to exocytic trafficking recycling) of NHE3. A role for PDZ in trafficking of has been only of is plasma membrane A. M. B. J. M. G. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). In and to increases plasma membrane and to a S. J. 2001; PubMed Scopus Google Scholar). In kidney cells, the PDZ domain of and are for of the acid are for membrane the PDZ to and membrane of A. M. B. J. M. G. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). PDZ domain is with increased exocytic trafficking of S. J. 2001; PubMed Scopus Google Scholar). of the and to PDZ J. M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar, S. Y. A. K. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). are in which exocytic trafficking of to PDZ The of in of kidney cells is increased by an increased of exocytic trafficking that the PDZ domain A. M. B. J. M. G. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). increases exocytic trafficking of the and J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, A. M. PubMed Scopus Google Scholar). In the of increased trafficking M. J. Biol. Chem. 2001; 276: Full Text Full Text PDF PubMed Scopus Google Scholar). PDZ domain protein the of In the current study, demonstrated that LPA the exocytic but not of NHE3 in the of E3KARP. This is the first that exocytic of NHE3 by a mechanism that is dependent on a PDZ protein. PI 3-kinase is for exocytic trafficking of NHE3 under basal and conditions in PI 3-kinase and Akt been to increase the plasma membrane amount and activity of NHE3 in W. Johns D.C. Cha B. Cavet M. Park J. Tsichlis P. Donowitz M. J. Biol. Chem. 2001; 276: 31296-31304Abstract Full Text Full Text PDF PubMed Scopus (47) Google the current demonstrated that PI 3-kinase activity was increased by LPA Akt activity to PI 3-kinase and that stimulation of PI 3-kinase activity was for LPA to NHE3 activity and exocytic The assay for PI 3-kinase not by PI as is the and not opossum kidney PI 3-kinase. the of PI 3-kinase in stimulation of that rapid growth factor stimulation of NHE3 activity and amount were with an increase in PI 3-kinase amount and activity S. Tse M.E. Donowitz M. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google not that was an increase in the apical membrane PI 3-kinase that was for LPA stimulation of NHE3 activity. are that of PI 3-kinase in the recycling endosomal are the PI 3-kinase plays an essential role in the LPA-induced stimulation of the LPA-induced Akt is not by the expression of E3KARP, with the E3KARP of the LPA-induced NHE3 The lack of Akt that the Akt is in LPA stimulation of NHE3 activity, and is that LPA-induced stimulation of NHE3 by a PI but an LPA-induced rapid stimulation of sodium absorption in has not been LPA is an mediator that is increased in amount a in inflammation and has been to in the restitution phase of inflammation Y. K.E. 2002; PubMed Scopus Google Scholar). sodium absorption and is not that stimulation of sodium absorption part of the The of the LPA stimulation of NHE3 on which is of Full Text Full Text PDF PubMed Scopus Google Scholar). LPA to in the stimulation of sodium absorption that in the treatment of In a that LPA the inflammation and in the acid of A. J. G. 2002; PubMed Scopus Google Scholar). to LPA stimulation of NHE3 activity is to the inflammation and The mechanism by which E3KARP increases LPA-induced exocytic trafficking of NHE3 is not is that E3KARP increases in LPA-induced that are to exocytosis of NHE3 to the apical plasma membrane. LPA plasma membrane and in cells has been to and and Y. K.E. 2002; PubMed Scopus Google Scholar, 2002; PubMed Scopus Google Scholar, K. N. G. 2002; PubMed Scopus Google Scholar). in cells, LPA rapidly PI 3-kinase in OK and in OK cells with a effect and growth factor 3-kinase and a O. Biol. PubMed Scopus Google Scholar, Full Text Full Text PDF PubMed Scopus Google Scholar, A. A. P. A. G. Acad. Sci. S. A. 1998; PubMed Scopus Google Scholar, K. Am. J. Physiol. 276: Google Scholar). of are to LPA stimulation of NHE3 is not the of PI 3-kinase. However, demonstrated that not by LPA in OK cells is in stimulation of NHE3. In study, demonstrated that LPA increased activity and phosphorylation, LPA of with not LPA stimulation of that is not in NHE3 is which LPA-induced are by E3KARP, the of E3KARP with and protein kinase W. Park Yun Donowitz M. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, Y. F. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, K. Yun J. Biol. Chem. 2000; 275: Full Text Full Text PDF PubMed Scopus Google that E3KARP in LPA-induced NHE3 with a that is by for the E3KARP of the LPA-induced NHE3 is that E3KARP NHE3 by a in exocytic and M. 2001; PubMed Scopus Google Scholar, A. M. Biol. 2002; PubMed Scopus Google several of and in which PDZ to act as the recycling compartment to the plasma to for is that E3KARP act as a by of the exocytic with of of PI the LPA stimulation of NHE3 prevented by the that PI as by Akt activity was not by the of E3KARP that the effect of E3KARP on LPA stimulation of NHE3 was on the exocytic that are of Akt LPA stimulation of NHE3 which in the in the exocytic trafficking by LPA are for LPA-induced NHE3 are to Tse and of and for the of