Phosphoinositide 3-hydroxide kinase blockade enhances apoptosis in the Ewing's sarcoma family of tumors.
Ewing's sarcoma family of tumors (ESFTs) affects patients between the ages of 3 and 40 years, with most cases occurring in the second decade of life. These tumors contain a characteristic translocation, t(11;22), that produces a unique fusion protein, EWS/FLI-1. EWS/FLI-1 transforms mouse fibroblasts; this transformation requires intact EWS and FLI-1 domains as well as the insulin-like growth factor-I receptor (IGF-IR). The IGF-IR is a well-described transmembrane tyrosine kinase receptor that modulates transformation, cell growth, and survival. IGF-IR survival signaling is mediated through the downstream activation of phosphoinositide 3-OH kinase (PI 3-K) and Akt. Apoptosis, programmed cell death, progresses from a central death signal to a caspase cascade, including activation of caspase-3. Because the IGF-IR has been shown to play a role in the transformation and growth of ESFTs, we wanted to determine the role of downstream molecules in the cellular response to doxorubicin treatment. Doxorubicin increased caspase-3 activity in two ESFT cell lines, TC-32 and TC-71. Concomitant treatment of the doxorubicin-treated cells with IGF-I reduced caspase-3 activity 8-fold in TC-32 and 4-fold in TC-71. To determine whether PI 3-K has a role in IGF-I-mediated survival in ESFTs, PI 3-K was then inhibited with wortmannin and LY294002. Doxorubicin treatment reduced cell number and enhanced apoptosis in PI 3-K inhibited cells compared with noninhibited cells. Akt, a serine/threonine kinase activated downstream of PI 3-K, was investigated to determine whether its constitutive activation would render ESFT cells more resistant to doxorubicin. A constitutively activated Akt was stably transfected into ESFT and those cells with high levels of expression demonstrated increased resistance to doxorubicin-induced caspase-3 activation. These results indicate that ESFT cell lines use an IGF-IR initiated signaling pathway through PI 3-K and Akt for survival when treated with doxorubicin.
Toretsky
J A
JA
Department of Pediatrics, University of Maryland, Baltimore 21201, USA. jt@helix.nih.gov
Thakar
M
M
Eskenazi
A E
AE
Frantz
C N
CN
D000730:Androstadienes / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced; D053938:DNA Fragmentation; D004317:Doxorubicin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D020287:In Situ Nick-End Labeling; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1; D012512:Sarcoma, Ewing / Q000201:enzymology* / Q000503:physiopathology; D014407:Tumor Cells, Cultured / Q000187:drug effects; D000077191:Wortmannin
D000730:Androstadienes; D000970:Antineoplastic Agents; D053148:Caspase 3; D020169:Caspases; D004317:Doxorubicin; D004791:Enzyme Inhibitors; D007334:Insulin-Like Growth Factor I; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017526:Receptor, IGF Type 1; D000077191:Wortmannin; C494918:AKT1 protein, human; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse