title: Suppression of cyclic GMP-specific phosphodiesterase 5 promotes apoptosis and inhibits growth in HT29 cells.
abstract: 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. In cloned antisense cells, prolongation of the cell growth doubling times correlate positively with suppressed PDE5 activity and increased [cGMP]i. The growth inhibition in PDE5 antisense clones is due to an increased apoptotic rate and delayed cell-cycle progression. These results corroborate previous findings with the PDE5 inhibitor exisulind and its derivatives showing that sustained [cGMP]i induces apoptosis and growth inhibition in tumor cells. Furthermore, an inducible mitotic inhibitor p21WAF1/CIP1 has been found to account for the delay of cell-cycle progression in PDE5 antisense clones at G2/M phase. A proteolytic cleavage of p21WAF1/CIP1 in the antisense clones is also increased at the later stage of serum stimulation. The protein kinase G (PKG) inhibitor, KT5823, can prevent the cleavage of p21(WAF1/CIP). These data substantiate a pivotal role for PDE5 as a modulator of apoptosis and cell-cycle progression for human carcinoma via a mechanism involving the activation of [cGMP]i/PKG signaling pathways.
authors.affiliation: Department of Pharmacology, University of South Alabama College of Medicine, Mobile, Alabama 36688, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Zhu
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Vemavarapu
authors.forename: W Joseph
authors.initials: WJ
authors.lastname: Thompson
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Strada
mesh_terms: D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000037:antagonists & inhibitors*; D000230:Adenocarcinoma / Q000201:enzymology / Q000473:pathology*; D017209:Apoptosis; D015153:Blotting, Western; D002227:Carbazoles / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000502:physiology; D003110:Colonic Neoplasms / Q000201:enzymology / Q000473:pathology*; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000378:metabolism; D016373:DNA, Antisense; D016195:G2 Phase / Q000502:physiology; D019073:HT29 Cells; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: C493956:CDKN1A protein, human; D002227:Carbazoles; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D016373:DNA, Antisense; D007211:Indoles; C073601:KT 5823; D017869:Cyclic GMP-Dependent Protein Kinases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; C517381:PDE5A protein, human