STAT3-activated GM-CSFR? translocates to the nucleus and protects CLL cells from apoptosis.

ABSTRACT: Here, it was determined that chronic lymphocytic leukemia (CLL) cells express the ? subunit, but not the ? subunit, of the granulocyte-macrophage colony-stimulating factor receptor (GM-CSFR/CSF2R). GM-CSFR? was detected on the surface, in the cytosol, and in the nucleus of CLL cells via confocal microscopy, cell fractionation, and GM-CSFR? antibody epitope mapping. Because STAT3 is frequently activated in CLL and the GM-CSFR? promoter harbors putative STAT3 consensus binding sites, MM1 cells were transfected with truncated forms of the GM-CSFR? 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-CSFR? mRNA and protein levels. RNA transcripts, involved in regulating cell survival pathways, and the proteins KAP1 (TRIM28) and ISG15 coimmunoprecipitated with GM-CSFR?. GM-CSFR?-bound KAP1 enhanced the transcriptional activity of STAT3, whereas GM-CSFR?-bound ISG15 inhibited the NF-?B pathway. Nevertheless, overexpression of GM-CSFR? protected MM1 cells from dexamethasone-induced apoptosis, and GM-CSFR? knockdown induced apoptosis in CLL cells, suggesting that GM-CSFR? provides a ligand-independent survival advantage.Constitutively, activation of STAT3 induces the expression of GM-CSFR? that protects CLL cells from apoptosis, suggesting that inhibition of STAT3 or GM-CSFR? may benefit patients with CLL.

SUBMITTER: Li P 

PROVIDER: S-EPMC4163508 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature