casein-kinase-ii and Leukemia--Myeloid

HOXA9 expression is a common feature of acute myeloid leukemia, and high-level expression is correlated with poor prognosis. Moreover, HOXA9 overexpression immortalizes murine marrow progenitors that are arrested at a promyelocytic stage of differentiation when cultured and causes leukemia in recipient mice following transplantation of HOXA9 expressing bone marrow. The molecular mechanisms underlying the physiologic functions and transforming properties of HOXA9 are poorly understood. This study demonstrates that HOXA9 is phosphorylated by protein kinase C (PKC) and casein kinase II and that PKC mediates phosphorylation of purified HOXA9 on S204 as well as on T205, within a highly conserved consensus sequence, in the N-terminal region of the homeodomain. S204 in the endogenous HOXA9 protein was phosphorylated in PLB985 myeloid cells, as well as in HOXA9-immortalized murine marrow cells. This phosphorylation was enhanced by phorbol ester, a known inducer of PKC, and was inhibited by a specific PKC inhibitor. PKC-mediated phosphorylation of S204 decreased HOXA9 DNA binding affinity in vitro and the ability of the endogenous HOXA9 to form cooperative DNA binding complexes with PBX. PKC inhibition significantly reduced the phorbol-ester induced differentiation of the PLB985 hematopoietic cell line as well as HOXA9-immortalized murine bone marrow cells. These data suggest that phorbol ester-induced myeloid differentiation is in part due to PKC-mediated phosphorylation of HOXA9, which decreases the DNA binding of the homeoprotein.

Topics: Amino Acid Sequence; Animals; Bone Marrow Cells; Casein Kinase II; Cell Differentiation; Cell Line; DNA-Binding Proteins; Enzyme Activation; Homeodomain Proteins; Isoenzymes; Leukemia, Myeloid; Mice; Molecular Sequence Data; Myeloid Cells; Phorbol Esters; Phosphorylation; Protein Binding; Protein Kinase C; Protein Serine-Threonine Kinases; Serine

Human recombinant CK2 subunits were incubated for different times with the two main cytosolic proteases m-calpain and 20 S proteasome. Both, m-calpain in a calcium dependent manner and the 20 S proteasome, were able to degrade CK2 subunits in vitro. In both cases, CK2alpha' was more resistant to these proteases than CK2alpha. When these proteases were assayed on the reconstituted (alpha2beta2 holoenzyme), a 37 kDa alpha-band, analogous to that observed in AML extracts, was generated which was resistant to further degradation. No degradation was observed when the 26 S proteasome was assayed on free subunits. Studies with CK2alpha deletion mutants showed that m-calpain and the 20 S proteasome acted on the C-terminus end of CK2alpha. These results pointed to cytosolic proteases as agents involved in the control of the amount of free CK2 subunits within the cell, which becomes evident when CK2 is overexpressed as in AML cells.

Topics: Acute Disease; Amino Acid Sequence; Animals; Calpain; Casein Kinase II; Cysteine Endopeptidases; HL-60 Cells; Humans; Hydrolysis; Isoenzymes; Leukemia, Myeloid; Multienzyme Complexes; Proteasome Endopeptidase Complex; Protein Serine-Threonine Kinases; Rabbits; Recombinant Proteins

Treatment of HL-60 with phorbol myristate acetate (PMA) for 30 min, or all-trans retinoic acid (RA) for 60 min, results in hyperphosphorylation (3-5x) of topoisomerase II (p170, topo II) in vivo. RA and PMA activate a coprecipitating kinase, respectively inducing 1.6 and 2.7-fold increases in phosphorylation of topo II in immunoprecipitates. The activity of the co-precipitating kinase is inhibited by heparin and unlabelled GTP suggesting that casein kinase II (CKII) is, at least in part, responsible for the topo II hyperphosphorylation in response to differentiation signals. Although following dephosphorylation of the enzyme with alkaline phosphatase there was virtual abrogation of activity, the differentiation associated hyperphosphorylation had little impact on the decatenation activity of topo II in nuclear extracts. There were, however detectable changes in topo II function in vivo which affected the formation of the etoposide stabilised cleavable complex, but only after PMA treatment. PMA resulted in a rapid reduction in etoposide induced cleavage, 30 min treatment with PMA reducing cleavage by 20%. However, treatment with RA for 1 or 2 h when hyperphosphorylation was maximal did not affect cleavage. Immunoband depletion assays suggested that differentiation associated changes in chromatin structure rather than alterations in the enzyme per se are responsible for the reduction in cleavable complex formation following PMA treatment. Etoposide cytotoxicity was significantly reduced following just 30 min PMA treatment, but not reduced and even possibly enhanced by retinoic acid treatment. These findings are relevant not only to the dissection of the role of topo II in differentiation but also to its exploitation as a therapeutic target.

Topics: Antigens, Neoplasm; Casein Kinase II; Cell Differentiation; Cell Nucleus; Cell Survival; DNA Topoisomerases, Type II; DNA-Binding Proteins; Enzyme Activation; Etoposide; Humans; In Vitro Techniques; Isoenzymes; Leukemia, Myeloid; Peptide Mapping; Phorbol Esters; Phosphorylation; Protein Serine-Threonine Kinases; Time Factors; Tretinoin; Tumor Cells, Cultured