title: A SOCS-1 peptide mimetic inhibits both constitutive and IL-6 induced activation of STAT3 in prostate cancer cells.
abstract: Prostate cancer is the second highest cause of cancer-related deaths of men in the US. Signal transducers and activators of transcription (STATs) proteins are a small family of latent cytoplasmic transcription factors that act downstream of Janus kinase (JAK) activation and mediate intracellular signaling from a wide variety of cytokines, growth factors, and hormones. Aberrant activation of STAT3 has been implicated in the progression of many human carcinomas, including prostate cancer. Previously, we have characterized a novel tyrosine kinase inhibitor peptide, Tkip, that is a mimetic of suppressor of cytokine signaling 1 (SOCS-1). Similar to SOCS-1, Tkip binds to the autophosphorylation site of JAK2 and inhibits phosphorylation of STAT1alpha. In this study, we determined the inhibitory effects of Tkip on the human prostate cancer cell lines DU145 and LNCaP. Tkip inhibited cellular proliferation of both DU145 and LNCaP cells, with a slightly greater antiproliferative effect on DU145 cells. Cell cycle analysis using flow cytometry showed Tkip blockage of progression into the S phase of the cell cycle. Tkip also inhibited constitutive (DU145) and IL-6-induced (LNCaP) activation of STAT3, consistent with the fact that STAT3 activation is mediated by JAK2. Tkip also slightly reduced the levels of cyclin D1, an important regulator of cell cycle progression into S phase, in DU145 and LNCaP cancer cell lines. These data describe a potentially important therapeutic that targets both constitutive and IL-6-induced STAT3 activation in human prostate cancer cell lines.
authors.affiliation: Department of Microbiology and Cell Science, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Lawrence O
authors.initials: LO
authors.lastname: Flowers
authors.forename: Prem S
authors.initials: PS
authors.lastname: Subramaniam
authors.forename: Howard M
authors.initials: HM
authors.lastname: Johnson
mesh_terms: D000595:Amino Acid Sequence; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D015850:Interleukin-6 / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D053614:Janus Kinase 2; D008297:Male; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology*; D011471:Prostatic Neoplasms; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050796:STAT3 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D015850:Interleukin-6; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C108944:SOCS1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D000071222:Suppressor of Cytokine Signaling 1 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2