title: Caveolin-1 maintains activated Akt in prostate cancer cells through scaffolding domain binding site interactions with and inhibition of serine/threonine protein phosphatases PP1 and PP2A.
abstract: Previously it has been reported that caveolin-1 (cav-1) has antiapoptotic activities in prostate cancer cells and functions downstream of androgenic stimulation. In this study, we demonstrate that cav-1 overexpression significantly reduced thapsigargin (Tg)-stimulated apoptosis. Examination of the phosphatidylinositol 3-kinase (PI3-K)/Akt signaling cascade revealed higher activities of PDK1 and Akt but not PI3-K in cav-1-stimulated cells compared to control cells. We subsequently found that cav-1 interacts with and inhibits serine/threonine protein phosphatases PP1 and PP2A through scaffolding domain binding site interactions. Deletion of the cav-1 scaffolding domain significantly reduces phosphorylated Akt and cell viability compared with wild-type cav-1. Analysis of potential substrates for PP1 and PP2A revealed that cav-1-mediated inhibition of PP1 and PP2A leads to increased PDK1, Akt, and ERK1/2 activities. We demonstrate that increased Akt activities are largely responsible for cav-1-mediated cell survival using dominant-negative Akt mutants and specific inhibitors to MEK1/MEK and show that cav-1 increases the half-life of phosphorylated PDK1 and Akt after inhibition of PI3-K by LY294002. We further demonstrate that cav-1-stimulated Akt activities lead to increased phosphorylation of multiple Akt substrates, including GSK3, FKHR, and MDM2. In addition, overexpression of cav-1 significantly increases translocation of phosphorylated androgen receptor to nucleus. Our studies therefore reveal a novel mechanism of Akt activation in prostate cancer and potentially other malignancies.
authors.affiliation: Scott Department of Urology, Baylor College of Medicine, 6560 Fannin, Suite 2100, Houston, TX 77030, USA.
authors.forename: Likun
authors.initials: L
authors.lastname: Li
authors.forename: Cheng Hui
authors.initials: CH
authors.lastname: Ren
authors.forename: Salahaldin A
authors.initials: SA
authors.lastname: Tahir
authors.forename: Chengzhen
authors.initials: C
authors.lastname: Ren
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Thompson
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D021581:Active Transport, Cell Nucleus; D001665:Binding Sites; D051242:Caveolin 1; D022461:Caveolins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection
chemical_list: C495540:CAV1 protein, human; D051242:Caveolin 1; D022461:Caveolins; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D019284:Thapsigargin; D064413:3-Phosphoinositide-Dependent Protein Kinases; C494918:AKT1 protein, human; C578562:PDPK1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D010749:Phosphoprotein Phosphatases