Cyclic AMP (cAMP) and cGMP regulate a myriad of cellular functions, such as metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system. Considerable effort over the last 20 years has allowed identification of the cellular components involved in the synthesis of cyclic nucleotides, as well as effectors of cyclic nucleotide-mediated signaling. More recently, a central role for cyclic nucleotide phosphodiesterase (PDE) has also been elaborated in many cell types, including those involved in regulating the activities of the cardiovascular system. In this review, we introduce the PDE families whose members are expressed in cells of the cardiovascular system including cardiomyocytes, vascular smooth muscle cells, and vascular endothelial cells. Because cell behavior is a dynamic process influenced by numerous factors, we will attempt to emphasize how changes in the activity, expression, and targeting of PDE influence cyclic nucleotide-mediated regulation of the behavior of these cells.The cyclic nucleotides cAMP and cGMP regulate a myriad of cellular functions, including metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system (Antoni, 2000;Klein, 2002). Although early work identified cAMP and cGMP as second messengers and led to the discovery of the proteins involved in coordinating the synthesis, degradation, and cellular actions of cyclic nucleotides, early models describing how these systems allowed cyclic nucleotide-mediated regulation of multiple cellular functions underestimated the levels of flexibility and specialization involved. In this context, recent work has identified large numbers of receptor (Marchese et al., 1999;Lucas et al., 2000), adenylyl cyclase (Hanoune and Defer, 2001), guanylyl cyclase (Garbers, 1999;Lucas et al., 2000), heterotrimeric G-protein (Marchese et al., 1999), and cyclic nucleotide phosphodiesterase (PDE) (Beavo and Reifsnyder, 1990;Beavo, 1995;Conti et al., 1995;Manganiello and Degerman, 1999;Conti, 2000;Conti and Jin, 2000;Houslay and Kolch, 2000;Soderling and Beavo, 2000;Francis et al., 2001;Houslay and Adams, 2003) protein families. Although many of the cellular effects of cAMP and cGMP are coordinated through their activation of cyclic nucleotide-dependent protein kinases (Lincoln et al., 1995), several other effectors are now known. Thus, cyclic nucleotidegated ion channels (Yau, 1994), cAMP-activated guanine nucleotide exchange factors (de Rooij et al., 1998;Kawasaki et al., 1998), and cyclic nucleotide PDEs have each been shown to transduce cyclic nucleotide-encoded information (Beavo and Reifsnyder, 1990;Beavo, 1995;Conti et al., 1995;Manganiello and Degerman, 1999;Conti, 2000;Conti and Jin, 2000;Houslay and Kolch, 2000;Soderling and Beavo, 2000;Francis et al., 2001;Houslay and Adams, 2003). More recently, an appreciation of the impact of regulated anchoring/targeting of cyclic nucleotide-regulated proteins to discrete subcell...

Epithelial-mesenchymal-transition (EMT) is a fundamental cellular process that is critical for normal development and tumor metastasis. The transforming growth factor beta (TGFβ) is a potent inducer of EMT like effects, but the mechanisms that regulate TGFβ-induced EMT remain incompletely understood. Using the widely employed NMuMG mammary epithelial cells as a model to study TGFβ-induced EMT, we report that TGFβ downregulates the levels of the SUMO E3 ligase PIAS1 in cells undergoing EMT. Gain and loss of function analyses indicate that PIAS1 acts in a SUMO ligase dependent manner to suppress the ability of TGFβ to induce EMT in these cells. We also find that TGFβ inhibits sumoylation of the PIAS1 substrate SnoN, a transcriptional regulator that antagonizes TGFβ-induced EMT. Accordingly, loss of function mutations of SnoN sumoylation impair the ability of SnoN to inhibit TGFβ-induced EMT in NMuMG cells. Collectively, our findings suggest that PIAS1 is a novel negative regulator of EMT and reveal that inhibition of the PIAS1-SnoN sumoylation pathway represents a key mechanism by which TGFβ induces EMT, with important implications in normal development and tumor metastasis.

Angiogenesis is necessary during embryonic development and wound healing but can be detrimental in pathologies, including cancer. Because initiation of angiogenesis involves migration and proliferation of vascular endothelial cells (VECs) and cAMPelevating agents inhibit these events, such agents may represent a novel therapeutic avenue to controlling angiogenesis. Intracellular cAMP levels are regulated by their synthesis by adenylyl cyclases and hydrolysis by cyclic nucleotide phosphodiesterases (PDEs). In this report, we show that human VECs express variants of PDE2, PDE3, PDE4, and PDE5 families and demonstrate that the levels of these enzymes differ in VECs derived from aorta, umbilical vein, and microvascular structures. Selective inhibition of PDE2 did not increase cAMP in any VECs, whether in the absence or presence of forskolin, but it did inhibit migration of all VECs studied. Inhibition of PDE4 activity decreased migration, and in conjunction with forskolin, increased cAMP in all VECs studied. PDE3 inhibition potentiated forskolin-induced increases in cAMP and inhibited migration in VECs derived from aorta and umbilical vein but not in microvascular VECs. In experiments with combinations of PDE2, PDE3, and PDE4 inhibitors, a complex interaction between the abilities of these agents to limit human VEC migration was observed. Overall, our data are consistent with the hypothesis that PDE subtype inhibition allows different effects in distinct VEC populations and indicate that these agents may represent novel therapeutic agents to limit angiogenesis in complex human diseases.

The transcriptional modulator SnoN controls a diverse set of biological processes, including cell proliferation and differentiation. The mechanisms by which SnoN regulates these processes remain incompletely understood. Recent studies have shown that SnoN exerts positive or negative regulatory effects on transcription. Because post-translational modification of proteins by small ubiquitin-like modifier (SUMO) represents an important mechanism in the control of the activity of transcriptional regulators, we asked if this modification regulates SnoN function. Here, we show that SnoN is sumoylated. Our data demonstrate that the SUMO-conjugating E2 enzyme Ubc9 is critical for SnoN sumoylation and that the SUMO E3 ligase PIAS1 selectively interacts with and enhances the sumoylation of SnoN. We identify lysine residues 50 and 383 as the SUMO acceptor sites in SnoN. Analyses of SUMO "loss-of-function" and "gain-of-function" SnoN mutants in transcriptional reporter assays reveal that sumoylation of SnoN contributes to the ability of SnoN to repress gene expression in a promoter-specific manner. Although this modification has little effect on SnoN repression of the plasminogen activator inhibitor-1 promoter and only modestly potentiates SnoN repression of the p21 promoter, SnoN sumoylation robustly augments the ability of SnoN to suppress transcription of the myogenesis master regulatory gene myogenin. In addition, we show that the SnoN SUMO E3 ligase, PIAS1, at its endogenous levels, suppresses myogenin transcription. Collectively, our findings suggest that SnoN is directly regulated by sumoylation leading to the enhancement of the ability of SnoN to repress transcription in a promoterspecific manner. Our study also points to a physiological role for SnoN sumoylation in the control of myogenin expression in differentiating muscle cells.

Epithelial-mesenchymal transition (EMT) is a fundamental cellular process in epithelial tissue development, and can be reactivated in cancer contributing to tumor invasiveness and metastasis. The cytokine transforming growth factor-β (TGFβ) is a key inducer of EMT, but the mechanisms that regulate TGFβ-induced EMT remain incompletely understood. Here, we report that knockdown of the ubiquitin ligase Smurf2 promotes the ability of TGFβ to induce EMT in a three-dimensional cell culture model of NMuMG mammary epithelial cells. In other studies, we identify Smurf2 as a target of the small ubiquitin like modifier (SUMO) pathway. We find that the SUMO-E2 conjugating enzyme Ubc9 and the SUMO E3 ligase PIAS3 associate with Smurf2 and promote its sumoylation at the distinct sites of Lysines 26 and 369. The sumoylation of Smurf2 enhances its ability to induce the degradation of the TGFβ receptor and thereby suppresses EMT in NMuMG cells. Collectively, our data reveal that Smurf2 acts in a sumoylationregulated manner to suppress TGFβ-induced EMT. These findings have significant implications for our understanding of epithelial tissue development and cancer. Cell Death and Differentiation (2016) 23, 876-888; doi:10.1038/cdd.2015; published online 18 December 2015Epithelial-mesenchymal transition (EMT) is an essential process in epithelial tissue morphogenesis in the developing organism and contributes to postnatal events including mammary postnatal gland development as well as wound healing.1,2 Importantly, EMT can be reactivated during cancer and may contribute to tumor invasiveness.3 Epithelial cells undergoing EMT change phenotypically from cuboidal to fibroblastic morphology, lose epithelial markers including E-cadherin, gain mesenchymal markers, and display increased cell motility and invasiveness. 4,5 The secreted factor transforming growth factor-β (TGFβ) has emerged as a potent inducer of EMT with key roles in development and cancer.6 Thus, there has been interest in the mechanisms that mediate TGFβ-induced EMT.Smurf2 (Smad (Sma and mad) ubiquitination regulatory factor-2) is a HECT (for homology to E6 carboxy terminus domain)-containing E3 ubiquitin ligase that specifies substrates for ubiquitination and degradation by the proteasome.7,8 Smurf2 regulates key biological processes during development and homeostasis including cell polarity, cell cycle, and senescence in an E3 ligase-dependent or -independent manner.9-15 The biological functions of Smurf2 occur via regulation of signaling pathways including the TGFβ-Smad signaling pathway. [16][17][18][19][20][21][22][23] However, the role of Smurf2 in TGFβ-induced EMT has remained to be determined.Sumoylation refers to the covalent attachment of the small ubiquitin-like modifier (SUMO), to protein substrates by the SUMO pathway.24 SUMO is linked to its substrates by an iso-peptide bond between C-terminal carboxyl group of SUMO and ε-amino group of a lysine residue in the substrate. The SUMO E2 conjugating enzyme Ubc9, the second enzyme of a three-step catalytic cascade...