title: The cAMP phosphodiesterase-4D7 (PDE4D7) is downregulated in androgen-independent prostate cancer cells and mediates proliferation by compartmentalising cAMP at the plasma membrane of VCaP prostate cancer cells.
abstract: BACKGROUND
  Isoforms of the PDE4 family of cAMP-specific phosphodiesterases (PDEs) are expressed in a cell type-dependent manner and contribute to underpinning the paradigm of intracellular cAMP signal compartmentalisation. Here we identify the differential regulation of the PDE4D7 isoform during prostate cancer progression and uncover a role in controlling prostate cancer cell proliferation.
  
  
  METHODS
  PDE4 transcripts from 19 prostate cancer cell lines and xenografts were quantified by qPCR. PDE4D7 expression was further investigated because of its significant downregulation between androgen-sensitive (AS) and androgen-insensitive (AI) samples. Western blot analysis, PDE activity assay, immunofluorescent staining and cAMP responsive FRET assays were used to investigate the sub-plasma membrane localisation of a population of PDE4D7 in VCaP (AS) and PC3 (AI) cell lines. Disruption of this localisation pattern using dominant-negative protein expression and siRNA knockdown showed that PDE4D7 acts in opposition to proliferative signalling as assessed by electrical impedance-based proliferation assays.
  
  
  RESULTS
  Here we identify the differential regulation of the PDE4D7 isoform during prostate cancer progression. PDE4D7 is highly expressed in AS cells and starkly downregulated in AI samples. The significance of this downregulation is underscored by our finding that PDE4D7 contributes a major fraction of cAMP degrading PDE activity tethered at the plasma membrane and that displacement of PDE4D7 from this compartment leads to an increase in the proliferation of prostate cancer cells. PDE4D7 mRNA expression is not, however, directly regulated by the androgen receptor signalling axis despite an overlapping genomic structure with the androgen responsive gene PART1. PDE4D7, which locates to the plasma membrane, acts to supress aberrant non-steroidal growth signals within the prostate or AS metastasis.
  
  
  CONCLUSIONS
  PDE4D7 expression is significantly downregulated between AS and AI cell phenotypes. This change in expression potentially provides a novel androgen-independent biomarker and manipulation of its activity or its expression may provide therapeutic possibilities and insights into contributory aspects of the complex molecular pathology of prostate cancer.
authors: Institute of Cardiovascular and Medical Sciences, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK.
authors: D J P
authors: DJ
authors: Henderson
authors: Institute of Cardiovascular and Medical Sciences, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK.
authors: A
authors: A
authors: Byrne
authors: Philips Research Eindhoven, Molecular Diagnostics, HTC11.1.165, 5656AE Eindhoven, The Netherlands.
authors: K
authors: K
authors: Dulla
authors: Erasmus MC, PO box 2040, 3000 CA Rotterdam, The Netherlands.
authors: G
authors: G
authors: Jenster
authors: Philips Research Eindhoven, Molecular Diagnostics, HTC11.1.165, 5656AE Eindhoven, The Netherlands.
authors: R
authors: R
authors: Hoffmann
authors: Institute of Cardiovascular and Medical Sciences, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK.
authors: G S
authors: GS
authors: Baillie
authors: Institute of Pharmaceutical Science, KCL, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK.
authors: M D
authors: MD
authors: Houslay
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000235:genetics / Q000378:metabolism*; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D007527:Isoenzymes; D008297:Male; D064129:Prostatic Neoplasms, Castration-Resistant / Q000201:enzymology* / Q000378:metabolism*; D011944:Receptors, Androgen / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: C410798:AR protein, human; D007527:Isoenzymes; D011944:Receptors, Androgen; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; C517376:PDE4D protein, human