In response to numerous pathologic stimuli, the myocardium undergoes a hypertrophic response characterized by increased myocardial cell size and activation of fetal cardiac genes. We show that cardiac hypertrophy is induced by the calcium-dependent phosphatase calcineurin, which dephosphorylates the transcription factor NF-AT3, enabling it to translocate to the nucleus. NF-AT3 interacts with the cardiac zinc finger transcription factor GATA4, resulting in synergistic activation of cardiac transcription. Transgenic mice that express activated forms of calcineurin or NF-AT3 in the heart develop cardiac hypertrophy and heart failure that mimic human heart disease. Pharmacologic inhibition of calcineurin activity blocks hypertrophy in vivo and in vitro. These results define a novel hypertrophic signaling pathway and suggest pharmacologic approaches to prevent cardiac hypertrophy and heart failure.

Members of the myocyte enhancer factor-2 (MEF2) family of transcription factors associate with myogenic basic helix-loop-helix transcription factors such as MyoD to activate skeletal myogenesis. MEF2 proteins also interact with the class II histone deacetylases HDAC4 and HDAC5, resulting in repression of MEF2-dependent genes. Execution of the muscle differentiation program requires release of MEF2 from repression by HDACs, which are expressed constitutively in myoblasts and myotubes. Here we show that HDAC5 shuttles from the nucleus to the cytoplasm when myoblasts are triggered to differentiate. Calcium/calmodulin-dependent protein kinase (CaMK) signalling, which stimulates myogenesis and prevents formation of MEF2-HDAC complexes, also induces nuclear export of HDAC4 and HDAC5 by phosphorylation of these transcriptional repressors. An HDAC5 mutant lacking two CaMK phosphorylation sites is resistant to CaMK-mediated nuclear export and acts as a dominant inhibitor of skeletal myogenesis, whereas a cytoplasmic HDAC5 mutant is unable to block efficiently the muscle differentiation program. Our results highlight a mechanism for transcriptional regulation through signal- and differentiation-dependent nuclear export of a chromatin-remodelling enzyme, and suggest that nucleo-cytoplasmic trafficking of HDACs is involved in the control of cellular differentiation.

Autophagy is primarily considered a non-selective degradation process induced by starvation. Nutrient-independent basal autophagy, in contrast, imposes intracellular QC by selective disposal of aberrant protein aggregates and damaged organelles, a process critical for suppressing neurodegenerative diseases. The molecular mechanism that distinguishes these two fundamental autophagic responses, however, remains mysterious. Here, we identify the ubiquitin-binding deacetylase, histone deacetylase-6 (HDAC6), as a central component of basal autophagy that targets protein aggregates and damaged mitochondria. Surprisingly, HDAC6 is not required for autophagy activation; rather, it controls the fusion of autophagosomes to lysosomes. HDAC6 promotes autophagy by recruiting a cortactin-dependent, actin-remodelling machinery, which in turn assembles an F-actin network that stimulates autophagosome-lysosome fusion and substrate degradation. Indeed, HDAC6 deficiency leads to autophagosome maturation failure, protein aggregate build-up, and neurodegeneration. Remarkably, HDAC6 and F-actin assembly are completely dispensable for starvation-induced autophagy, uncovering the fundamental difference of these autophagic modes. Our study identifies HDAC6 and the actin cytoskeleton as critical components that define QC autophagy and uncovers a novel regulation of autophagy at the level of autophagosome-lysosome fusion.

Skeletal muscle differentiation is controlled by associations between myogenic basic-helix-loop-helix and MEF2 transcription factors. We show that chromatin associated with muscle genes regulated by these transcription factors becomes acetylated during myogenesis and that class II histone deacetylases (HDACs), which interact with MEF2, specifically suppress myoblast differentiation. These HDACs do not interact directly with MyoD, yet they suppress its myogenic activity through association with MEF2. Elevating the level of MyoD can override the repression imposed by HDACs on muscle genes. HDAC-mediated repression of myogenesis also can be overcome by CaM kinase and insulin-like growth factor (IGF) signaling. These findings reveal central roles for HDACs in chromatin remodeling during myogenesis and as intranuclear targets for signaling pathways controlled by IGF and CaM kinase.

Compared to normal cells, cancer cells strongly upregulate glucose uptake and glycolysis to give rise to increased yield of intermediate glycolytic metabolites and the end product pyruvate. Moreover, glycolysis is uncoupled from the mitochondrial tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) in cancer cells. Consequently, the majority of glycolysis-derived pyruvate is diverted to lactate fermentation and kept away from mitochondrial oxidative metabolism. This metabolic phenotype is known as the Warburg effect. While it has become widely accepted that the glycolytic intermediates provide essential anabolic support for cell proliferation and tumor growth, it remains largely elusive whether and how the Warburg metabolic phenotype may play a role in tumor progression. We hereby review the cause and consequence of the restrained oxidative metabolism, in particular in tumor metastasis. Cells change or lose their extracellular matrix during the metastatic process. Inadequate/inappropriate matrix attachment generates reactive oxygen species (ROS) and causes a specific type of cell death, termed anoikis, in normal cells. Although anoikis is a barrier to metastasis, cancer cells have often acquired elevated threshold for anoikis and hence heightened metastatic potential. As ROS are inherent byproducts of oxidative metabolism, forced stimulation of glucose oxidation in cancer cells raises oxidative stress and restores cells’ sensitivity to anoikis. Therefore, by limiting the pyruvate flux into mitochondrial oxidative metabolism, the Warburg effect enables cancer cells to avoid excess ROS generation from mitochondrial respiration and thus gain increased anoikis resistance and survival advantage for metastasis. Consistent with this notion, pro-metastatic transcription factors HIF and Snail attenuate oxidative metabolism, whereas tumor suppressor p53 and metastasis suppressor KISS1 promote mitochondrial oxidation. Collectively, these findings reveal mitochondrial oxidative metabolism as a critical suppressor of metastasis and justify metabolic therapies for potential prevention/intervention of tumor metastasis.

Myocyte enhancer factor-2 (MEF2) transcription factors control muscle-specific and growth factor-inducible genes. We show that hypertrophic growth of cardiomyocytes in response to phenylephrine and serum is accompanied by activation of MEF2 through a posttranslational mechanism mediated by calcium, calmodulindependent protein kinase (CaMK), and mitogen-activated protein kinase (MAPK) signaling. CaMK stimulates MEF2 activity by dissociating class II histone deacetylases (HDACs) from the DNA-binding domain. MAPKs, which activate MEF2 by phosphorylation of the transcription activation domain, maximally stimulate MEF2 activity only when repression by HDACs is relieved by CaMK signaling to the DNA-binding domain. These findings identify MEF2 as an endpoint for hypertrophic stimuli in cardiomyocytes and demonstrate that MEF2 mediates synergistic transcriptional responses to the CaMK and MAPK signaling pathways by signal-dependent dissociation from HDACs.M yocyte enhancer factor-2 (MEF2) transcription factors (1) participate in diverse gene regulatory programs, including those for muscle and neural differentiation, cardiac morphogenesis, blood vessel formation, and growth factor responsiveness (reviewed in ref.2). The four MEF2 factors, MEF2A, -B, -C, and -D, share high homology in an amino-terminal MADS (MCMI, Agamous, Deficiens, Serum response factor) domain that mediates DNA-binding and dimerization and an adjacent MEF2-specific domain that influences DNA-binding affinity and interaction with transcriptional cofactors (2). The carboxyl-terminal regions of MEF2 factors, which are more divergent, act as transcription activation domains (TADs).Studies in T cells and fibroblasts have shown that the mitogenactivated protein kinases (MAPKs) p38 and ERK5 stimulate transcriptional activity of MEF2 factors by phosphorylating conserved sites in their TADs (3-12). Calcium, calmodulindependent protein kinase (CaMK), and calcineurin also stimulate MEF2 activity (13,14), but the underlying mechanisms are unknown. It is also unclear whether MAPK, CaMK, and calcineurin pathways cross-talk or act in parallel to activate MEF2.Most studies of MEF2 activation by extracellular signaling have focused on cells that are highly responsive to mitogens. Whether MEF2 retains the ability to respond to growth factor signals in terminally differentiated muscle cells, which are permanently postmitotic, and whether MEF2 is activated in muscle cells by the same signaling pathways as in other cell types has not been determined. In cardiac myocytes, growth factor signals evoke a hypertrophic response characterized by cell enlargement, activation of immediate early genes, reactivation of fetal cardiac muscle genes, and sarcomere assembly (reviewed in ref. 15).To investigate the mechanisms that regulate MEF2 activity in response to extracellular signals and to test whether MEF2 retains its ability to respond to growth factor signals in terminally differentiated muscle cells, we sought to determine whether MEF2 could be activated by hypertrophic signals ...

Breast cancer is the most common cancer and the second leading cause of cancer-related deaths in American women. Paclitaxel

PICK1 is a protein kinase C (PKC) ␣-binding protein initially identified using the yeast two-hybrid system. Here we report that PICK1 contains a PDZ domain that interacts specifically with a previously unidentified PDZ-binding domain (QSAV) at the extreme COOH terminus of PKC␣ and that mutation of a putative carboxylate-binding loop within the PICK1 PDZ domain abolishes this interaction. The PDZ-binding domain in PKC␣ is absent from other PKC isoforms that do not interact with PICK1. We also demonstrate that PICK1 can homooligomerize through sequences that are distinct from the carboxylate-binding loop, suggesting that self-association and PKC␣ binding are not mutually exclusive. A Caenorhabditis elegans PICK1-like protein is also able to bind to PKC␣, suggesting a conservation of function through evolution. Association of PKC␣ with PICK1 provides a potential mechanism for the selective targeting of PKC␣ to unique subcellular sites.