Role of PI3 kinase gamma in excitation-contraction coupling and heart disease.

Class I phosphoinositide 3-kinases (PI3Ks) are enzymes with both protein and lipid kinase activities that have ubiquitous cellular functions. In the heart, subclass IA PI3Ks, PI3K-alpha and beta, regulate cell growth, apoptosis, cell division and cell size, whereas PI3Kgamma, the only member of subclass IB, has been shown to regulate myocardial contractility. Loss of p110gamma, the catalytic subunit of PI3Kgamma, enhances cardiac excitation-contraction coupling by modulating cyclic adenosine monophosphate (cAMP) levels in subcellular domains containing the sarcoplasmic reticulum (SR) leading to increased cAMP-mediated phosphorylation of phospholamban. The ability of p110gamma to modulate cAMP is likely mediated by the protein-protein interactions with the cAMP-degrading enzymes, phosphodiesterases, independent of its lipid kinase activity. PI3Kgamma also plays a key role in modulating the cAMP response and desensitization of beta-adrenergic receptors. Loss of p110gamma gamma leads to acute decompensation and rapid progression into heart failure in response to pathological biomechanical stress while lipid kinase-dead mutants were relatively resistant suggesting that elevated intracellular cAMP (and its secondary effects) is an important predisposing factor for heart failure. The commercial availability of specific PI3Kgamma inhibitors may be used as therapeutic agents in inflammatory and cardiovascular diseases. In this review article, we discuss the key role of PI3Kgamma gamma in regulating cAMP, Ca(2+) cycling, beta-adrenergic signaling and myocardial structure and function in heart disease.