CREB expression in cardiac fibroblasts and CREM expression in ventricular myocytes

Activation of gene expression by the cAMP-dependent signaling pathway is regulated by members of the cAMP response element binding protein (CREB) family consisting of CREB, CREM, and ATF-1. It is decisively for the understanding of the heart function as to which type of heart cells expresses CREB and/or CREM. Ventricular myocytes and fibroblasts of young (3 months) and old (24 months) rat hearts were separately investigated to analyse CREB, CREM, and phospho-CREB. Western blot showed CREB expression exclusively in fibroblasts but CREM was predominantly detected in ventricular myocytes. CREB-positive nuclei in heart sections were only revealed in fibroblasts. CREB was activated by forskolin (10 microM), PMA (500 nM), and cyclical mechanical strain (1 Hz, 5% elongation) in fibroblasts. The number of CREB-positive myocytes in old rats was larger than in young rats. But CREB could not be activated by forskolin (10 microM) in all myocytes. Our results suggest that the expression of CREB depends on the cell type and the age of the animal. We discuss that modulation of gene expression as it occurs with a age could be affected by the change within the CREB family members.     

Role of cAMP and phosphodiesterase signaling in liver health and disease

Liver disease is a significant health problem worldwide with mortality reaching around 2 million deaths a year. Non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are the major causes of chronic liver disease. Pathologically, NAFLD and ALD share similar patterns of hepatic disorders ranging from simple steatosis to steatohepatitis, fibrosis and cirrhosis. It is becoming increasingly important to identify new pharmacological targets, given that there is no FDA-approved therapy yet for either NAFLD or ALD. Since the evolution of liver diseases is a multifactorial process, several mechanisms involving parenchymal and non-parenchymal hepatic cells contribute to the initiation and progression of liver pathologies. Moreover, certain protective molecular pathways become repressed during liver injury including signaling pathways such as the cyclic adenosine monophosphate (cAMP) pathway. cAMP, a key second messenger molecule, regulates various cellular functions including lipid metabolism, inflammation, cell differentiation and injury by affecting gene/protein expression and function. This review addresses the current understanding of the role of cAMP metabolism and consequent cAMP signaling pathway(s) in the context of liver health and disease. The cAMP pathway is extremely sophisticated and complex with specific cellular functions dictated by numerous factors such abundance, localization and degradation by phosphodiesterases (PDEs). Furthermore, because of the distinct yet divergent roles of both of its effector molecules, the cAMP pathway is extensively targeted in liver injury to modify its role from physiological to therapeutic, depending on the hepatic condition. This review also examines the behavior of the cAMP-dependent pathway in NAFLD, ALD and in other liver diseases and focuses on PDE inhibition as an excellent therapeutic target in these conditions.     

Essential role of A-kinase anchor protein 121 for cAMP signaling to mitochondria

A-Kinase anchor proteins (AKAPs) immobilize and concentrate protein kinase A (PKA) isoforms at specific subcellular compartments. Intracellular targeting of PKA holoenzyme elicits rapid and efficient phosphorylation of target proteins, thereby increasing sensitivity of downstream effectors to cAMP action. AKAP121 targets PKA to the cytoplasmic surface of mitochondria. Here we show that conditional expression of AKAP121 in PC12 cells selectively enhances cAMP.PKA signaling to mitochondria. AKAP121 induction stimulates PKA-dependent phosphorylation of the proapoptotic protein BAD at Ser(155), inhibits release of cytochrome c from mitochondria, and protects cells from apoptosis. An AKAP121 derivative mutant that localizes on mitochondria but does not bind PKA down-regulates PKA signaling to the mitochondria and promotes apoptosis. These findings indicate that PKA anchored by AKAP121 transduces cAMP signals to the mitochondria, and it may play an important role in mitochondrial physiology.     

A pivotal role for CXCL12 signaling in HPV-mediated transformation of keratinocytes: clues to understanding HPV-pathogenesis in WHIM syndrome

The WHIM syndrome, which features high susceptibility to human papillomavirus (HPV) infection, is a rare immunodeficiency associated with autosomal dominant heterozygous mutations of the CXCR4 chemokine receptor. CXCL12 and its receptors, CXCR4 and CXCR7, are linked to tumorigenesis, and we reported that abnormal expression of CXCL12 in epidermal keratinocytes correlates with HPV infection. However, the HPV-related pathologies observed in WHIM patients remain mechanistically unexplained. We show that keratinocytes immortalized by oncogenic HPV16 or HPV18 upregulate CXCL12 and its receptors in a manner dependent upon expression of the viral proteins E6 and E7. Autocrine signaling activated by CXCL12-engagement of its receptors controls motility and survival of the infected cells. Strikingly, expression of a WHIM syndrome-related gain-of-function CXCR4 mutant confers transforming capacity to HPV18-immortalized keratinocytes. These results establish a pivotal role for CXCL12 signaling in HPV-mediated transformation and provide a mechanistic basis for understanding HPV pathogenesis in WHIM syndrome.     

CREB and cAMP response element-mediated gene expression in the ischemic brain

Cerebral ischemia triggers robust phosphorylation of cAMP response element-binding protein (CREB) and CRE-mediated gene expression in neurons. Glutamate receptor activation and subsequent calcium influx may activate CREB shortly after ischemia. CREB activation leads to expression of genes encoding neuroprotective molecules, such as the antiapoptotic protein Bcl-2, and contributes to survival of neurons after ischemic insult. Recent studies have suggested that CREB may be involved in acquisition of ischemic tolerance, a phenomenon that occurs after sublethal ischemic stress. CREB activation is also involved in the survival of newborn neurons in the dentate gyrus of the hippocampus after ischemia. Therefore, CREB-related therapeutics may be promising for brain protection and endogenous neurogenesis and could promote functional recovery in ischemic stroke patients. This minireview summarizes our current understanding for the role of CREB in regulating CRE-mediated gene expression during cerebral ischemia.     

CSCDB: the cAMP and cGMP signaling components database

Adenylate cyclases, guanylate cyclases, cyclic nucleotide phosphodiesterases, and cyclic nucleotide-binding proteins constitute the core of cAMP and cGMP signaling components. Using a combination of BLAST and profile search methods, we found that cyclic nucleotide-binding proteins exhibited diverse domain architectures. In addition to the domain architectures involved in the characterized functional groups, a cyclic nucleotide-binding domain was also fused to various domains involved in pyridine nucleotide-disulfide oxidoreductase, acetyltransferase, thioredoxin reductase, glutaminase, rhodanese, ferredoxin, and diguanylate cyclase, implying the versatile functions of cyclic nucleotide-binding proteins. We constructed the CSCDB database to accumulate the components of cAMP and cGMP signaling pathways in the complete genomes. User-friendly interfaces were created for easier browsing, searching, and downloading the data. Besides harboring the sequence itself, each entry provided detailed annotation information, such as sequence features, chromosomal localization, functional domains, transmembrane region, and sequence similarity against several major databases. Currently, CSCDB contains 4234 entries covering 466 organisms, including 35 eukaryotes, 382 bacteria, and 29 archaea. CSCDB can be freely accessible on the web at http://cscdb.com.cn.