STAT3-activated GM-CSFRα translocates to the nucleus and protects CLL cells from apoptosis.
Here, it was determined that chronic lymphocytic leukemia (CLL) cells express the α subunit, but not the β subunit, of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR/CSF2R). GM-CSFRα was detected on the surface, in the cytosol, and in the nucleus of CLL cells via confocal microscopy, cell fractionation, and GM-CSFRα antibody epitope mapping. Because STAT3 is frequently activated in CLL and the GM-CSFRα promoter harbors putative STAT3 consensus binding sites, MM1 cells were transfected with truncated forms of the GM-CSFRα promoter, then stimulated with IL6 to activate STAT3 and to identify STAT3-binding sites. Chromatin immunoprecipitation (ChIP) and an electoromobility shift assay (EMSA) confirmed STAT3 occupancy to those promoter regions in both IL6-stimulated MM1 and CLL cells. Transfection of MM1 cells with STAT3-siRNA or CLL cells with STAT3-shRNA significantly downregulated GM-CSFRα mRNA and protein levels. RNA transcripts, involved in regulating cell survival pathways, and the proteins KAP1 (TRIM28) and ISG15 coimmunoprecipitated with GM-CSFRα. GM-CSFRα-bound KAP1 enhanced the transcriptional activity of STAT3, whereas GM-CSFRα-bound ISG15 inhibited the NF-κB pathway. Nevertheless, overexpression of GM-CSFRα protected MM1 cells from dexamethasone-induced apoptosis, and GM-CSFRα knockdown induced apoptosis in CLL cells, suggesting that GM-CSFRα provides a ligand-independent survival advantage.


CONCLUSIONS
Constitutively, activation of STAT3 induces the expression of GM-CSFRα that protects CLL cells from apoptosis, suggesting that inhibition of STAT3 or GM-CSFRα may benefit patients with CLL.
Departments of Leukemia and.
Ping
P
Li
Departments of Leukemia and.
David
D
Harris
Departments of Leukemia and.
Zhiming
Z
Liu
Departments of Leukemia and.
Uri
U
Rozovski
Departments of Leukemia and.
Alessandra
A
Ferrajoli
Departments of Leukemia and.
Yongtao
Y
Wang
Hematopathology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
Carlos
C
Bueso-Ramos
Departments of Leukemia and.
Inbal
I
Hazan-Halevy
Departments of Leukemia and.
Srdana
S
Grgurevic
Departments of Leukemia and.
William
W
Wierda
Departments of Leukemia and.
Jan
J
Burger
Departments of Leukemia and.
Susan
S
O'Brien
Departments of Leukemia and.
Stefan
S
Faderl
Departments of Leukemia and.
Michael
M
Keating
Departments of Leukemia and zestrov@mdanderson.org.
Zeev
Z
Estrov
D017209:Apoptosis / Q000235:genetics; D002470:Cell Survival / Q000235:genetics; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D016328:NF-kappa B / Q000378:metabolism; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor / Q000235:genetics / Q000378:metabolism*; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics; D014178:Translocation, Genetic
C521678:CSF2RA protein, human; D016328:NF-kappa B; D034741:RNA, Small Interfering; D016187:Receptors, Granulocyte-Macrophage Colony-Stimulating Factor; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human