title: Inhibition of constitutive activation of STAT3 by curcurbitacin-I (JSI-124) sensitized human B-leukemia cells to apoptosis.
abstract: Phosphorylation of STAT3 on serine 727 regulates gene expression and is found to be elevated in many B-leukemia cells including chronic lymphocytic leukemia (CLL). It is, however, unclear whether targeting STAT3 will be an effective antileukemia therapy. In this study, we assessed in vitro antileukemia activity of the STAT3 inhibitor JSI-124 (cucurbitacin I). JSI-124 potently induces apoptosis in 3 B-leukemia cell lines (BJAB, I-83, and NALM-6) and in primary CLL cells and was associated with a reduction in serine 727 phosphorylation of STAT3. Similarly, knockdown of STAT3 expression induced apoptosis in these leukemia cells. In addition, we found that JSI-124 and knockdown of STAT3 decreased antiapoptotic protein XIAP expression and overexpression of XIAP blocked JSI-124-induced apoptosis. Furthermore, we found that combined treatment of JSI-124 and TRAIL increased apoptosis associated with an increase in death receptor 4 expression. Besides apoptosis, we found that JSI-124 also induced cell-cycle arrest prior to apoptosis in B-leukemia cells. This corresponded with reduced expression of the cell-cycle regulatory gene, cdc-2. Thus, we present here for the first time that JSI-124 induced suppression of serine 727 phosphorylation of STAT3, leading to apoptosis and cell-cycle arrest through alterations in gene transcription in B-leukemia cells.
authors.affiliation: Departments of Biochemistry and Medical Genetics, Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Ganchimeg
authors.initials: G
authors.lastname: Ishdorj
authors.forename: James B
authors.initials: JB
authors.lastname: Johnston
authors.forename: Spencer B
authors.initials: SB
authors.lastname: Gibson
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000187:drug effects; D004354:Drug Screening Assays, Antitumor; D055785:Gene Knockdown Techniques; D056284:Histone Deacetylase 1 / Q000378:metabolism; D006801:Humans; D015448:Leukemia, B-Cell / Q000378:metabolism / Q000473:pathology*; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism / Q000473:pathology; D010768:Phosphoserine / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000494:pharmacology; D014315:Triterpenes / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism
chemical_list: D034741:RNA, Small Interfering; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D053221:TNF-Related Apoptosis-Inducing Ligand; D014315:Triterpenes; D051636:X-Linked Inhibitor of Apoptosis Protein; D010768:Phosphoserine; C110550:HDAC1 protein, human; D056284:Histone Deacetylase 1; C038106:cucurbitacin I