350 Biochemical Society Transactions (2004) Volume 32, part 2 Physiological functions of protein kinase B/Akt Z.-Z. Yang, O. Tschopp, A. Baudry, B. D ¨ ummler, D. Hynx and B.A. Hemmings 1 Friedrich Miescher Institute for Biomedical Research, Maulbeerstrasse 66, CH-4058, Basel, Switzerland Abstract The genetic manipulation of mice has become an essential and elegant method for studying the function of proteins in physiology, and for testing the veracity of information obtained from cell culture experi- ments. During the past few years, a variety of transgenic and knockout mouse models of PKB (protein kinase B)/Akt have been generated and investigated. In this paper, we focus on the phenotypes of these PKB/Akt overexpression and mutant mice that may help to elucidate the functions exerted by PKB/Akt in mammals. Introduction Three PKB (protein kinase B)/Akt isoforms have been identified in mice and humans (for reviews, see [1–4]). These three PKB/Akt proteins, although encoded by distinct genes localized on different chromosomes, have approx. 80% amino acid identity and similar domain structures. Moreover, the differences between corresponding isoforms in humans and mice are subtle (between two and ten amino acid changes), which makes it feasible to determine the functions of PKB/Akt kinases in human physiology by studying them in the mouse. Stimulation by numerous growth factors, cytokines, hormones and neurotransmitters can activate PKB/Akt in a phosphoinositide 3-kinase-dependent manner (reviewed in [2,4]). Through receptor tyrosine kinases, these stimuli cause phosphoinositide 3-kinase activation, and generation of the membrane phospholipid PtdIns(3,4,5)P 3 . PtdIns(3,4,5)P 3 then recruits PKB/Akt to the membrane, where it becomes phosphorylated at Thr 308 and Ser 473 (for PKBα/Akt1) by two upstream kinases, phosphoinositide-dependent kinase 1 and a yet to be identified Ser 473 kinase. These processes of membrane targeting and activation of PKB/Akt can be facilitated and mimicked by adding the myristoyla- tion signal sequence of Lck/Src to the N-terminus of PKB/Akt (Myr-PKB/Akt) or by mutation of the two regulatory sites of PKB/Akt to acidic residues (PKB T308D/S473D in PKBα/Akt1) [4,5]. Myristoylation of PKB/Akt promotes constitutive membrane attachment and activation, and the T308D/S473D double mutant of PKB is constitutively active [4,5]. Based on these observations, Myr-PKB/Akt and PKB T308D/S473D have been commonly used for vector construction to generate transgenic mice [5]. Key words: Akt, gene knockout, protein kinase B, transgenic mouse model. Abbreviations used: DKO, double knockout, GBM, glioblastoma multiforme; α-MHC, α-myosin heavy chain; PKB, protein kinase B; PPAR, peroxisome proliferator-activated receptor; PTEN, phosphatase and tensin homologue deleted on chromosome 10. 1 To whom correspondence should be addressed (e-mail hemmings@ fmi.ch). PKB/Akt transgenic mice Overexpression of PKB/Akt in tissues The first PKB/Akt transgenic mouse model was reported in 2000 [6]. Since then, more than 10 PKB/Akt transgenic mouse lines have been produced. Constructs of PKB/Akt and the tissues targeted are summarized in Table 1. At least two mouse lines have been generated for the thymus, heart, pancreas and mammary glands. A single line has been generated for the prostate. Tissue-specific promoters were used to drive overexpression of PKB/Akt in these different tissues. PKB/Akt was either myristoylated for membrane targeting (activation) or mutated to double Asp (T308D/S473D) for constitutive activation. Hypertrophy and increased contractility with PKB/Akt overexpression in the heart The α-MHC (α-myosin heavy chain) promoter has been utilized extensively to drive transgenic expression exclusively in cardiac myocytes [23]. Three of the four PKB/Akt trans- genic mouse lines directly use this promoter to drive PKB/ Akt overexpression in the heart. In the fourth line, PKB/Akt transcription is under the control of a tetracycline-responsive promoter that reacts to α-MHC-directed expression of the tetracycline-controlled transactivator [7–11]. The most readily apparent phenotype of these mice was sudden death of some founders with massive cardiac dilatation [7]. Viable derived transgenic mouse lines showed cardiac hypertrophy, with an approx. 2-fold increase in heart weight. The increase in heart weight was associated with larger cardiac myocytes [7,9,10]. These mice also showed a remarkable increase in cardiac contractility and a reduction in infarct size after ischaemia/reperfusion compared with wild-type controls [7,10]. Overexpression of PKB/Akt in the heart also caused higher p70 S6K phosphorylation, and reduced AMP-activated protein kinase activity [7,9,11]. The transcriptional effects of this chronic activation of PKB/Akt in the heart were analysed using DNA microarrays to determine altered gene expression profiles. Of the C  2004 Biochemical Society