STAT3 Activates GM-CSFR{alpha} in CLL

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-B 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-inde...

Source: Molecular Cancer Research - September 11, 2014 Category: Cancer & Oncology Authors: Li, P., Harris, D., Liu, Z., Rozovski, U., Ferrajoli, A., Wang, Y., Bueso-Ramos, C., Hazan-Halevy, I., Grgurevic, S., Wierda, W., Burger, J., O'Brien, S., Faderl, S., Keating, M., Estrov, Z. Tags: Genomics Source Type: research