title: A cell-permeable Stat3 SH2 domain mimetic inhibits Stat3 activation and induces antitumor cell effects in vitro.
abstract: Given the role of constitutively active Signal Transducer and Activator of Transcription (Stat) 3 in human tumors, Stat3 inhibitors would be useful as novel therapeutics and as tools for probing Stat3-mediated tumor processes. We herein report that a 28-mer peptide, SPI, derived from the Stat3 SH2 domain, replicates Stat3 biochemical properties. Studies show SPI and Stat3 (or Stat3 SH2 domain) bind with similar affinities to known Stat3-binding phosphotyrosine (pY) peptide motifs, including those of the epidermal growth factor receptor (EGFR) and the high-affinity, IL-6R/gp130-derived pY-peptide, GpYLPQTV-NH(2). Consequently, SPI functions as a potent and selective inhibitor of Stat3 SH2 domain:pTyr interactions and disrupts the binding of Stat3 to the IL-6R/gp130 peptide, GpYLPQTV-NH(2). Fluorescence imaging and immunofluorescence staining/laser-scanning confocal microscopy show SPI is cell membrane-permeable, associates with the cytoplasmic tail of EGFR in NIH3T3/hEGFR, and is present in the cytoplasm, but strongly localized at the plasma membrane and in the nucleus in malignant cells harboring persistently active Stat3. Moreover, SPI specifically blocks constitutive Stat3 phosphorylation, DNA binding activity, and transcriptional function in malignant cells, with little or no effect on the induction of Stat1, Stat5, and Erk1/2(MAPK) pathways, or on general pTyr profile at the concentrations that inhibit Stat3 activity. Significantly, treatment with SPI of human breast, pancreatic, prostate, and non-small cell lung cancer cells harboring constitutively active Stat3 induced extensive morphology changes, associated with viability loss and apoptosis. Our study identifies SPI as a novel molecular probe for interrogating Stat3 signaling and that functions as a selective inhibitor of Stat3 activation with antitumor cell effects.
authors.affiliation: Burnett School of Biomedical Sciences, University of Central Florida College of Medicine, Orlando, Florida 32827, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.forename: Soumya
authors.initials: S
authors.lastname: Jaganathan
authors.forename: James
authors.initials: J
authors.lastname: Turkson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000970:Antineoplastic Agents / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002463:Cell Membrane Permeability; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D051379:Mice; D018613:Microscopy, Confocal; D008958:Models, Molecular; D008969:Molecular Sequence Data; D041681:NIH 3T3 Cells; D010455:Peptides / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D050796:STAT3 Transcription Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018909:src Homology Domains
chemical_list: D000970:Antineoplastic Agents; D010455:Peptides; D050796:STAT3 Transcription Factor
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