title: Enforced expression of Bcl-XS induces differentiation and sensitizes chronic myelogenous leukemia-blast crisis K562 cells to 1-beta-D-arabinofuranosylcytosine-mediated differentiation and apoptosis.
abstract: Human chronic myelogenous leukemia-blast crisis K562 cells have been demonstrated to be relatively resistant to antileukemic drug-induced apoptosis. This has been attributed to the activity of p210bcr-abl tyrosine kinase present in the K562 cells, which is known to suppress drug-induced apoptosis. Recently, K562 cells have been shown to express the antiapoptosis Bcl-xL but not Bcl-2 proteins. To investigate the contribution of Bcl-xL toward resistance to drug-induced apoptosis, we created K562/Bcl-xS and K562/neo cells by electroporating the expression plasmids pSFFVneo-Bcl-xS and pSFFVneo, containing the bcl-xS and neomycin resistance genes, respectively, into K562 cells. K562/Bcl-xS but not K562/neo cells expressed the bcl-xS mRNA and p19Bcl-xS protein. In contrast, both cell types expressed equivalent levels of Bcl-xL, Bax, Bcl-2, Myc, retinoblastoma, p21cbor-abl, and p145abl proteins. A significant increase in the hemoglobin levels was observed in the K562/Bcl-xS compared with the K562/neo cells (P < 0.05). In addition, K562/Bcl-xS cells were significantly more sensitive than K562/neo cells to undergoing erythroid differentiation induced by low-dose 1-beta-D-arabinofuranosylcytosine (ara-C) and hexamethyl bisacetamide (P < 0.05), but not by all-trans-retinoic acid. Low-dose ara-C- or hexamethyl bisacetamide-induced differentiation was not associated with apoptosis of K562/Bcl-xS or K562/neo cells. Low-dose ara-C-induced erythroid differentiation was accompanied by conversion of the retinoblastoma protein to predominantly its underphosphorylated isoform as well as by down-regulation of Myc levels in K562/Bcl-xS and K562/neo cells. Importantly, exposure to high-dose ara-C (HIDAC; 100 microM ara-C for 4 h) caused internucleosomal DNA fragmentation and the morphological features of apoptosis in K562/Bcl-xS cells. These effects were modestly enhanced by cotreatment with HIDAC plus herbimycin A. In contrast, K562/neo cells were completely resistant to HIDAC- and herbimycin A-induced apoptosis. These results indicate that the expression of Bcl-xS induces erythroid differentiation and partially sensitizes chronic myelogenous leukemia-blast crisis-derived K562 cells to ara-C-induced differentiation and apoptosis.
authors.affiliation: Department of Medicine, Winship Cancer Center, Emory University School of Medicine, Atlenta, Georgia 30322, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ray
authors.forename: G
authors.initials: G
authors.lastname: Bullock
authors.forename: G
authors.initials: G
authors.lastname: Nuñez
authors.forename: C
authors.initials: C
authors.lastname: Tang
authors.forename: A M
authors.initials: AM
authors.lastname: Ibrado
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: K
authors.initials: K
authors.lastname: Bhalla
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015152:Blotting, Northern; D015153:Blotting, Western; D002454:Cell Differentiation / Q000502:physiology; D003561:Cytarabine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000502:physiology; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D018922:HL-60 Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D007951:Leukemia, Myeloid; D009355:Neomycin; D010957:Plasmids; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D014162:Transfection; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000964:Antimetabolites, Antineoplastic; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D003561:Cytarabine; D009355:Neomycin