The PML/RARalpha fusion protein inhibits tumor necrosis factor-alpha-induced apoptosis in U937 cells and acute promyelocytic leukemia blasts.
We investigated the effect of the acute promyelocytic leukemia (APL) specific PML/RARalpha fusion protein on the sensitivity to TNF-alpha-mediated apoptosis. The U937 leukemia cell line was transduced with PML/RARalpha cDNA. PML/RARalpha expression caused a markedly reduced sensitivity to TNF-alpha, even if apoptosis was triggered by agonistic antibodies to TNF-alpha receptors I and II (TNF-alphaRI, II). PML/RARalpha induced a 10-20-fold decrease of the TNF-alpha-binding capacity via downmodulation of both TNF-alphaRI and TNF-alphaRII: this may mediate at least in part the reduced sensitivity to TNF-alpha. Furthermore, the fusion protein did not modify Fas expression (CD95) or sensitivity to Fas-mediated apoptosis. The pathophysiological significance of these findings is supported by two series of observations. (a) Fresh APL blasts exhibit no TNF-alpha binding and are resistant to TNF-alpha-mediated apoptosis. Conversely, normal myeloblasts-promyelocytes show marked TNF-alphaR expression and are moderately sensitive to TNF-alpha-mediated cytotoxicity. Similarly, blasts from other types of acute myeloid leukemia (AML M1, M2, and M4 FAB types) show an elevated TNF-alpha binding. (b) The NB4 APL cell line, which is PML/RARalpha+, shows low TNF-alphaR expression capacity and is resistant to TNF-alpha-triggered apoptosis; conversely a PML/RARalpha- NB4 subclone (NB4.306) exhibits detectable TNF-alpha-binding capacity and is sensitive to TNF-alpha-mediated cytotoxicity. These studies indicate that the PML/RARalpha fusion protein protects against TNF-alpha-induced apoptosis, at least in part via downmodulation of TNF-alphaRI/II: this phenomenon may play a significant role in APL, which is characterized by prolonged survival of leukemic blasts.
Testa
U
U
Department of Hematology-Oncology, Istituto Superiore di Sanità, 00161 Rome, Italy.
Grignani
F
F
Samoggia
P
P
Zanetti
C
C
Riccioni
R
R
Lo Coco
F
F
Diverio
D
D
Felli
N
N
Passerini
C G
CG
Grell
M
M
Pelicci
P G
PG
Peschle
C
C
D015703:Antigens, CD / Q000032:analysis / Q000276:immunology; D017209:Apoptosis / Q000502:physiology*; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D015473:Leukemia, Promyelocytic, Acute / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D011485:Protein Binding / Q000187:drug effects; D012333:RNA, Messenger / Q000032:analysis; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D018124:Receptors, Tumor Necrosis Factor / Q000819:agonists / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000502:physiology*; D000072482:Retinoic Acid Receptor alpha; D014157:Transcription Factors / Q000235:genetics*; D014162:Transfection; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000633:toxicity*; D025521:Tumor Suppressor Proteins; D019014:fas Receptor / Q000378:metabolism
D015703:Antigens, CD; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; C000607071:RARA protein, human; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D018124:Receptors, Tumor Necrosis Factor; D011993:Recombinant Fusion Proteins; D000072482:Retinoic Acid Receptor alpha; D014157:Transcription Factors; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D019014:fas Receptor; C070576:PML protein, human