Abstract-␤-Adrenergic agonists stimulate cardiac contractility and simultaneously blunt this response by coactivating NO synthase (NOS3) to enhance cGMP synthesis and activate protein kinase G (PKG-1). cGMP is also catabolically regulated by phosphodiesterase 5A (PDE5A). PDE5A inhibition by sildenafil (Viagra) increases cGMP and is used widely to treat erectile dysfunction; however, its role in the heart and its interaction with ␤-adrenergic and NOS3/cGMP stimulation is largely unknown. In nontransgenic (control) murine in vivo hearts and isolated myocytes, PDE5A inhibition (sildenafil) minimally altered rest function. However, when the hearts or isolated myocytes were stimulated with isoproterenol, PDE5A inhibition was associated with a suppression of contractility that was coupled to elevated cGMP and increased PKG-1 activity. In contrast, NOS3-null hearts or controls with NOS inhibited by N G -nitro-Larginine methyl ester, or soluble guanylate cyclase (sGC) inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one, showed no effect of PDE5A inhibition on ␤-stimulated contractility or PKG-1 activation. This lack of response was not attributable to altered PDE5A gene or protein expression or in vitro PDE5A activity, but rather to an absence of sGC-generated cGMP specifically targeted to PDE5A catabolism and to a loss of PDE5A localization to z-bands. Re-expression of active NOS3 in NOS3-null hearts by adenoviral gene transfer restored PDE5A z-band localization and the antiadrenergic efficacy of PDE5A inhibition. These data support a novel regulatory role of PDE5A in hearts under adrenergic stimulation and highlight specific coupling of PDE5A catabolic regulation with NOS3-derived cGMP attributable to protein subcellular localization and targeted synthetic/catabolic coupling. Key Words: PDE5 Ⅲ phosphodiesterase Ⅲ sildenafil Ⅲ nitric oxide synthase Ⅲ contractility Ⅲ z-band B eta-adrenergic regulation of cardiac contraction is coupled to elevations in adenosine (cAMP) and guanosine (cGMP) cyclic nucleotides. Increased cAMP enhances contractility 1,2 by activating protein kinase A (PKA), whereas concomitant stimulation of cGMP opposes this in part by activating protein kinase G (PKG-1). 3,4 The latter response is thought to be attributable to stimulation of soluble guanylate cyclase (sGC) by NO. 3-9 Cyclic GMP is also synthesized by receptor GC (rGC) coupled to natriuretic peptide stimulation, and both sources can modulate cardiac function and structure, particularly in hearts stimulated by neurohormones or mechanical stress. 3-5,10 -13 cGMP is also regulated by catabolic phosphodiesterases such as phosphodiesterase 5A (PDE5A), and PDE5A inhibition by sildenafil (Viagra; SIL) and similar compounds augments cGMP in vascular tissue and is the primary therapy for erectile dysfunction. 14,15 However, the role for PDE5A in regulating cardiac function has remained unclear. 16 -18 Such clarification has become increasingly important because PDE5A inhibitors are poised to become chronic treatments for diseases such as pul...

Elevated levels of prostaglandin E 2 (PGE 2 ) are often found in colorectal cancers. Thus, nonsteroidal anti-inflammatory drugs, including selective cyclooxygenase-2 (COX-2) inhibitors, are among the most promising chemopreventive agents for colorectal cancer. However, their long-term use is restricted by the occurrence of adverse events believed to be associated with a global reduction in prostaglandin production. In the present study, we evaluated the chemopreventive efficacy of targeting the terminal synthase microsomal PGE 2 synthase 1 (mPGES-1), which is responsible for generating PGE 2 , in two murine models of intestinal cancer. We report for the first time that genetic deletion of mPGES-1 in Apc-mutant mice results in marked and persistent suppression of intestinal cancer growth by 66%, whereas suppression of large adenomas (>3 mm) was almost 95%. This effect occurred despite loss of Apc heterozygosity and B-catenin activation. However, we found that mPGES-1 deficiency was associated with a disorganized vascular pattern within primary adenomas as determined by CD31 immunostaining. We also examined the effect of mPGES-1 deletion on carcinogen-induced colon cancer. The absence of mPGES-1 reduced the size and number of preneoplastic aberrant crypt foci (ACF). Importantly, mPGES-1 deletion also blocked the nuclear accumulation of B-catenin in ACF, confirming that B-catenin is a critical target of PGE 2 procarcinogenic signaling in the colon. Our data show the feasibility of targeting mPGES-1 for cancer chemoprevention with the potential for improved tolerability over traditional nonsteroidal anti-inflammatory drugs and selective COX-2 inhibitors. [Cancer Res 2008;68(9):3251-9]