Akt Kinase Phosphorylation of Inositol 1,4,5-Trisphosphate Receptors

• Published in: The Journal of biological chemistry 2006-02, Vol.281 (6), p.3731-3737
• Main Authors: Khan, M. Tariq, Wagner, Larry, Yule, David I., Bhanumathy, Cunnigaiper, Joseph, Suresh K.
• Format: Article
• Language: English
• Subjects: Alanine - chemistry; Amino Acid Motifs; Amino Acid Sequence; Animals; Apoptosis; Calcium - metabolism; Calcium Channels - metabolism; Calcium-Transporting ATPases - metabolism; Caspase 3; Caspases - metabolism; Cell Line; Chlorocebus aethiops; CHO Cells; Chromones - pharmacology; COS Cells; Cricetinae; Detergents - pharmacology; DNA, Complementary - metabolism; Enzyme Activation; Glutamic Acid - chemistry; Humans; Immunoprecipitation; Inositol 1,4,5-Trisphosphate Receptors; Microcirculation - metabolism; Molecular Sequence Data; Morpholines - pharmacology; Octoxynol - pharmacology; Phosphatidylinositol 3-Kinases - metabolism; Phosphorylation; Proto-Oncogene Proteins c-akt - metabolism; Receptors, Cytoplasmic and Nuclear - metabolism; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Serine - chemistry; Staurosporine - pharmacology; Time Factors; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M509262200

A consensus RXRXX(S/T) substrate motif for Akt kinase is conserved in the C-terminal tail of all three inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) isoforms. We have shown that IP3R can be phosphorylated by Akt kinase in vitro and in vivo. Endogenous IP3Rs in Chinese hamster ovary T-cells were phosphorylated in response to Akt activation by insulin. LnCAP cells, a prostate cancer cell line with constitutively active Akt kinase, also showed a constitutive phosphorylation of endogenous type I IP3Rs. In all cases, the IP3R phosphorylation was diminished by the addition of LY294002, an inhibitor of phosphatidylinositol 3-kinase. Mutation of IP3R serine 2681 in the Akt substrate motif to alanine (S2681A) or glutamate (S2681E) prevented IP3R phosphorylation in COS cells transfected with constitutively active Akt kinase. Analysis of the Ca2+ flux properties of these IP3R mutants expressed in COS cell microsomes or in DT40 triple knock-out (TKO) cells did not reveal any modification of channel function. However, staurosporine-induced caspase-3 activation in DT40 TKO cells stably expressing the S2681A mutant was markedly enhanced when compared with wild-type or S2681E IP3Rs. We conclude that IP3 receptors are in vivo substrates for Akt kinase and that phosphorylation of the IP3R may provide one mechanism to restrain the apoptotic effects of calcium.