title: Constitutive Phosphorylation of STAT3 by the CK2-BLNK-CD5 Complex.
abstract: In chronic lymphocytic leukemia (CLL), STAT3 is constitutively phosphorylated on serine 727 and plays a role in the pathobiology of CLL. However, what induces constitutive phosphorylation of STAT3 is currently unknown. Mass spectrometry was used to identify casein kinase 2 (CK2), a serine/threonine kinase that coimmunoprecipitated with serine phosphorylated STAT3 (pSTAT3). Furthermore, activated CK2 incubated with recombinant STAT3 induced phosphorylation of STAT3 on serine 727. Although STAT3 and CK2 are present in normal B- and T cells, STAT3 is not constitutively phosphorylated in these cells. Further study found that CD5 and BLNK coexpressed in CLL, but not in normal B- or T cells, are required for STAT3 phosphorylation. To elucidate the relationship of CD5 and BLNK to CK2 and STAT3, STAT3 was immunoprecipitated from CLL cells, and CK2, CD5, and BLNK were detected in the immunoprecipitate. Conversely, STAT3, CD5, and BLNK were in the immunoprecipitate of CLL cells immunoprecipitated with CK2 antibodies. Furthermore, siRNA knockdown of CD5 or BLNK, or treatment with CD5-neutralizing antibodies significantly reduced the levels of serine pSTAT3 in CLL cells. Finally, confocal microscopy determined that CD5 is cell membrane bound, and fractionation studies revealed that the CK2/CD5/BLNK/STAT3 complex remains in the cytoplasm, whereas serine pSTAT3 is shuttled to the nucleus.Implications:These data show that the cellular proteins CK2, CD5, and BLNK are required for constitutive phosphorylation of STAT3 in CLL. Whether this protein complex phosphorylates other proteins or inhibiting its activity would have clinical benefit in patients has yet to be determined.Mol Cancer Res; 15(5); 610-8. ©2017 AACR.
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.|Division of Hematology, Davidoff Cancer Center, Rabin Medical Center, Petah Tiqva, Israel.|Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Uri
authors.initials: U
authors.lastname: Rozovski
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: David M
authors.initials: DM
authors.lastname: Harris
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Zhiming
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Preetesh
authors.initials: P
authors.lastname: Jain
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Ivo
authors.initials: I
authors.lastname: Veletic
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Ferrajoli
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Jan
authors.initials: J
authors.lastname: Burger
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Susan
authors.initials: S
authors.lastname: O'Brien
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Prithviraj
authors.initials: P
authors.lastname: Bose
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Philip
authors.initials: P
authors.lastname: Thompson
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Nitin
authors.initials: N
authors.lastname: Jain
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: William
authors.initials: W
authors.lastname: Wierda
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Keating
authors.affiliation: Department of Leukemia, The University of Texas MD Anderson Cancer Center, Houston, Texas. zestrov@mdanderson.org.
authors.forename: Zeev
authors.initials: Z
authors.lastname: Estrov
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D018956:CD5 Antigens / Q000378:metabolism*; D047390:Casein Kinase II / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D020014:K562 Cells; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000378:metabolism*; D013058:Mass Spectrometry; D010766:Phosphorylation; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D012694:Serine / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; D018956:CD5 Antigens; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D012694:Serine; D047390:Casein Kinase II