Protein kinase A phosphorylation of tau-serine 214 reorganizes microtubules and disrupts the endothelial cell barrier.

Intracellular cAMP is compartmentalized to near membrane domains in endothelium, where it strengthens endothelial cell barrier function. Phosphodiesterase 4D4 (PDE4D4) interacts with the spectrin membrane skeleton and prevents cAMP from accessing microtubules. Expression of a dominant-negative PDE4D4 peptide enables cAMP to access microtubules, where it results in phosphorylation of the nonneuronal microtubule-associated protein tau at serine 214.

Type 5 phosphodiesterase expression is a critical determinant of the endothelial cell angiogenic phenotype.

Type 5 phosphodiesterase (PDE5) inhibitors increase endothelial cell cGMP and promote angiogenesis. However, not all endothelial cell phenotypes express PDE5. Indeed, whereas conduit endothelial cells express PDE5, microvascular endothelial cells do not express this enzyme, and they are rapidly angiogenic.

The novel functions of cGMP-specific phosphodiesterase 5 and its inhibitors in carcinoma cells and pulmonary/cardiovascular vessels.

PDE5 is a key enzyme involved in the regulation of cGMP-specific signaling pathways in normal physiological processes such as smooth muscle contraction and relaxation. For this reason, inhibition of the enzyme can alter those pathophysiological conditions associated with a lowering cGMP level in tissues. For example, selective PDE5 inhibitors, such as sildenafil (Viagra, Pfizer), tadalafil (Cialis, Lilly-ICOS), and vardenafil (Levitra, Bayer), have been successfully used to treat the condition of human erectile dysfunction.

Chemoprevention of bicyclol against hepatic preneoplastic lesions.

Oral administration of 100 and 200 mg/kg body weight/day of 4,4-dimethoxy-5,6,5', 6'-dimethylene-dioxy-2-hydroxymethyl-2'-carbonyl biphenyl, Bicyclol, inhibited rat hepatic preneoplastic lesions induced by diethylnitrosamine (DEN). Bicyclol reduced densities of number and area of gamma-glutamyltransferase positive foci, indexes for neoplastic hyperplasia; and also suppressed protein expressions for glutathione S transferase P isoform (GST-P) and alpha-fetal protein and mRNA for N-ras, c-myc and PKCalpha genes. With increases of total microsomal P450 and specific CYP2B1 activities in normal rat liver, Bicyclol enhanced particularly the denitrosation of DEN, a low toxic pathway of metabolism.

Chemosensitizing multiple drug resistance of human carcinoma by Bicyclol involves attenuated p-glycoprotein, GST-P and Bcl-2.

Bicyclol, a second generation of synthetic hepatoprotectant being used in China for anti-hepatitis therapy, shows chemosensitizing effect on reverting multiple drug resistance (MDR) of cytostatic agents in two established MDR carcinoma cell lines, vincristine resistant human stomatic epidermoid carcinoma VinRKB and adriamycin resistant human breast carcinoma AdrRMCF-7. The reversal rate of drug resistance was calculated from the changes of the IC50 of cell growth inhibition. Bicyclol at the concentration of 25, 50, 100 microM induced 2.

8-chloroadenosine induced HL-60 cell growth inhibition, differentiation, and G(0)/G(1) arrest involves attenuated cyclin D1 and telomerase and up-regulated p21(WAF1/CIP1).

8-Chloroadenosine, an active dephosphorylated metabolite of the antineoplastic agent 8-chloroadenosine 3',5'-monophosphate (8-Cl-cAMP), induces growth inhibition in multiple carcinomas. Here we report that 8-chloroadenosine inhibits growth in human promyelocytic leukemia HL-60 cells by a G(0)/G(1) phase arrest and terminates cell differentiation along the granulocytic lineage. The mechanism of 8-chloroadenosine-induced G(0)/G(1) arrest is independent of apoptosis.

Suppression of cyclic GMP-specific phosphodiesterase 5 promotes apoptosis and inhibits growth in HT29 cells.

Phosphodiesterase 5 (PDE5) is a major isoform of cGMP phosphodiesterase in a variety of human tumor cell lines and plays a key role in regulating intracellular cGMP concentrations ([cGMP]i). Here, we demonstrate that suppression of PDE5 gene expression by antisense pZeoSV2/ASP5 plasmid transfection results in a sustained increase in [cGMP]i, growth inhibition, and apoptosis in human colon tumor HT29 cells. With stable transfection, antisense transcripts exhibited a specific suppression in PDE5 activity, mRNA levels, and a 93 kDa hPDE5A1 protein.

Activation and induction of cyclic AMP phosphodiesterase (PDE4) in rat pulmonary microvascular endothelial cells.

Regulation of the rolipram-sensitive cAMP-specific phosphodiesterase 4 (PDE4) gene family was studied in rat pulmonary microvascular endothelial cells (RPMVECs). Total PDE4 hydrolysis was increased within 10 min after addition of forskolin (10 microM), reached a maximum at 20-40 min, and then gradually declined in the cells. A similar activation of PDE4 activity was observed using a protein kinase A (PKA) activator, N(6)-monobutyryl cAMP.

Regulation of cyclic AMP in rat pulmonary microvascular endothelial cells by rolipram-sensitive cyclic AMP phosphodiesterase (PDE4).

We report here studies on the regulation of the metabolism of adenosine 3',5'-monophosphate (cAMP) in established and primary cultures of rat pulmonary microvascular endothelial cells (RPMVEC). Inhibition by rolipram, a selective inhibitor of cAMP phosphodiesterase (PDE) of the PDE4 gene family, was required to achieve maximal cAMP accumulation induced by direct or receptor-mediated adenylate cyclase activation when measured by [3H]-adenine prelabeling. Rolipram increased cAMP accumulation more effectively than did forskolin, isoproterenol, or adenosine derivatives alone, although extensive synergy was seen with combined agents.