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Vasopressin‐Induced Phosphorylation of PKB/Akt in the Rat Inner Medullary Collecting Duct
Author(s) -
Jacob Vinitha Anne,
Pisitkun T,
Yu MJ,
Knepper MA
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a905-c
Subject(s) - protein kinase b , phosphorylation , ly294002 , pi3k/akt/mtor pathway , chemistry , medicine , endocrinology , microbiology and biotechnology , kinase , biology , signal transduction , biochemistry
Our studies in isolated IMCD cell suspensions have demonstrated that vasopressin suppresses the MAPK pathway (decreased phosphorylation of ERK1/2 and MEK1 with increased phosphorylation of c‐Raf at the inhibitory site S259). Because protein kinase B (Akt) was implicated in S259 c‐Raf phosphorylation, we investigated whether Akt is activated by vasopressin. Semi‐quantitative immunoblotting of IMCD suspensions from rats was carried out after exposure to 1 nM vasopressin analog (dDAVP) or the vehicle in a pH/temperature‐controlled chamber for 1, 2, 5, 10, 15, and 30 min. dDAVP increased the phosphorylation of Akt at T308 and S473 (both sites associated with activation of kinase activity). The phosphorylation of PDK‐1, an upstream regulator of Akt, also increased in response to dDAVP. Confocal images of the IMCD showed a marked increase in pT308 Akt in the apical region of the cells after 1nM dDAVP. Redistribution of aquaporin‐2 to the apical plasma membrane confirmed the action of dDAVP. An inhibitor of PI3K (LY294002, 25 μM) blocked the increase in pT308 and pS473 of Akt. However, this inhibitor did not alter pS259 c‐Raf abundance. Finally, glycogen synthase kinase‐3β, another potential downstream target of Akt, did not exhibit a significant response to dDAVP at any point during the time course. In conclusion, dDAVP activates Akt via PI3K and PDK‐1 but the inhibition of the MAPK pathway does not depend on Akt activation.