The acquisition of resistance to apoptosis, the cell's intrinsic suicide program, is essential for cancers to arise and progress and is a major reason behind treatment failures. We show in this article that small molecule antagonists of the -1 receptor inhibit tumor cell survival to reveal caspase-dependent apoptosis. antagonist-mediated caspase activation and cell death are substantially attenuated by the prototypic -1 agonists (؉)-SKF10,047 and (؉)-pentazocine. Although several normal cell types such as fibroblasts, epithelial cells, and even receptor-rich neurons are resistant to the apoptotic effects of antagonists, cells that can promote autocrine survival such as lens epithelial and microvascular endothelial cells are as susceptible as tumor cells. Cellular susceptibility appears to correlate with differences in receptor coupling rather than levels of expression. In susceptible cells only, antagonists evoke a rapid rise in cytosolic calcium that is inhibited by -1 agonists. In at least some tumor cells, antagonists cause calcium-dependent activation of phospholipase C and concomitant calcium-independent inhibition of phosphatidylinositol 3-kinase pathway signaling. Systemic administration of antagonists significantly inhibits the growth of evolving and established hormone-sensitive and hormone-insensitive mammary carcinoma xenografts, orthotopic prostate tumors, and p53-null lung carcinoma xenografts in immunocompromised mice in the absence of side effects. Release of a receptor-mediated brake on apoptosis may offer a new approach to cancer treatment.

The cardiac phosphoprotein phospholemman (PLM) regulates the cardiac sodium pump, activating the pump when phosphorylated and inhibiting it when palmitoylated. Protein palmitoylation, the reversible attachment of a 16 carbon fatty acid to a cysteine thiol, is catalyzed by the Asp-His-His-Cys (DHHC) motif-containing palmitoyl acyltransferases. The cell surface palmitoyl acyltransferase DHHC5 regulates a growing number of cellular processes, but relatively few DHHC5 substrates have been identified to date. We examined the expression of DHHC isoforms in ventricular muscle and report that DHHC5 is among the most abundantly expressed DHHCs in the heart and localizes to caveolin-enriched cell surface microdomains. DHHC5 coimmunoprecipitates with PLM in ventricular myocytes and transiently transfected cells. Overexpression and silencing experiments indicate that DHHC5 palmitoylates PLM at two juxtamembrane cysteines, C40 and C42, although C40 is the principal palmitoylation site. PLM interaction with and palmitoylation by DHHC5 is independent of the DHHC5 PSD-95/Discslarge/ZO-1 homology (PDZ) binding motif, but requires a ∼120 amino acid region of the DHHC5 intracellular C-tail immediately after the fourth transmembrane domain. PLM C42A but not PLM C40A inhibits the Na pump, indicating PLM palmitoylation at C40 but not C42 is required for PLM-mediated inhibition of pump activity. In conclusion, we demonstrate an enzyme-substrate relationship for DHHC5 and PLM and describe a means of substrate recruitment not hitherto described for this acyltransferase. We propose that PLM palmitoylation by DHHC5 promotes phospholipid interactions that inhibit the Na pump.phospholemman | sodium pump | palmitoylation | DHHC | ion transport P rotein palmitoylation, the reversible attachment of a 16 carbon fatty acid to a cysteine thiol via a thioester bond, is catalyzed by Asp-His-His-Cys motif-containing palmitoyl acyltransferases (DHHC-PATs); there are 23 human isoforms (1). These zinc-finger-containing enzymes typically have four transmembrane (TM) domains, with a conserved ∼50 amino acid cysteine-rich cytosolic core located between TM2 and -3, which contains a conserved DHHC motif, the active site. In contrast, the intracellular amino and carboxyl termini are poorly conserved, and likely contribute to DHHC isoform substrate selectivity (1). DHHC-PATs are expressed throughout the secretory pathway, but DHHC5 is widely recognized as one of very few cell-surfacelocalized PATs (2, 3). The final four amino acids of DHHC5 form a canonical class II PSD-95/Discs-large/ZO-1 homology (PDZ) binding motif, which interacts with postsynaptic density protein 95 (PSD-95) (2), although PSD-95 is not itself a DHHC5 substrate.An appreciation is now growing that protein palmitoylation turns over rapidly (in minutes) for certain proteins (4-8). For example, dynamic surface membrane protein palmitoylation by DHHC5 underlies a novel form of endocytosis, massive endocytosis (MEND), in which up to 70% of the cell surface membrane is internalized (7, 8). Calci...

AMPK (AMP-activated protein kinase) is a heterotrimetric enzyme that is expressed in many tissues, including the heart and vasculature, and plays a central role in the regulation of energy homoeostasis. It is activated in response to stresses that lead to an increase in the cellular AMP/ATP ratio caused either by inhibition of ATP production (i.e. anoxia or ischaemia) or by accelerating ATP consumption (i.e. muscle contraction or fasting). In the heart, AMPK activity increases during ischaemia and functions to sustain ATP, cardiac function and myocardial viability. There is increasing evidence that AMPK is implicated in the pathophysiology of cardiovascular and metabolic diseases. A principle mode of AMPK activation is phosphorylation by upstream kinases [e.g. LKB1 and CaMK (Ca2+/calmodulin-dependent protein kinase], which leads to direct effects on tissues and phosphorylation of various downstream kinases [e.g. eEF2 (eukaryotic elongation factor 2) kinase and p70 S6 kinase]. These upstream and downstream kinases of AMPK have fundamental roles in glucose metabolism, fatty acid oxidation, protein synthesis and tumour suppression; consequently, they have been implicated in cardiac ischaemia, arrhythmias and hypertrophy. Recent mechanistic studies have shown that AMPK has an important role in the mechanism of action of MF (metformin), TDZs (thiazolinediones) and statins. Increased understanding of the beneficial effects of AMPK activation provides the rationale for targeting AMPK in the development of new therapeutic strategies for cardiometabolic disease.