Protein kinase CK2 regulates AKT, NF-κB and STAT3 activation, stem cell viability and proliferation in acute myeloid leukemia.

Protein kinase CK2 sustains acute myeloid leukemia cell growth, but its role in leukemia stem cells is largely unknown. Here, we discovered that the CK2 catalytic α and regulatory ß subunits are consistently expressed in leukemia stem cells isolated from acute myeloid leukemia patients and cell lines. CK2 inactivation with the selective inhibitor CX-4945 or RNA interference induced an accumulation of leukemia stem cells in the late S-G2-M phases of the cell cycle and triggered late-onset apoptosis. As a result, leukemia stem cells displayed an increased sensitivity to the chemotherapeutic agent doxorubicin. From a molecular standpoint, CK2 blockade was associated with a downmodulation of the stem cell-regulating protein BMI-1 and a marked impairment of AKT, nuclear factor-κB (NF-κB) and signal transducer and activator of transcription 3 (STAT3) activation, whereas FOXO3a nuclear activity was induced. Notably, combined CK2 and either NF-κB or STAT3 inhibition resulted in a superior cytotoxic effect on leukemia stem cells. This study suggests that CK2 blockade could be a rational approach to minimize the persistence of residual leukemia cells.

Targeting CK2-driven non-oncogene addiction in B-cell tumors.

Genetic mutations of oncogenes often underlie deranged cell growth and altered differentiation pathways leading to malignant transformation of B-lymphocytes. However, addiction to oncogenes is not the only drive to lymphoid tumor pathogenesis. Dependence on non-oncogenes, which act by propelling basic mechanisms of cell proliferation and survival, has also been recognized in the pathobiology of lymphoid leukemias, lymphomas and multiple myeloma. Among the growing number of molecules that may uphold non-oncogene addiction, a key place is increasingly being recognized to the serine-threonine kinase CK2. This enzyme is overexpressed and overactive in B-acute lymphoblastic leukemia, multiple myeloma, chronic lymphocytic leukemia and non-Hodgkin lymphomas, such as mantle cell, follicular, Burkitt's and diffuse large B-cell lymphomas. In these tumors, CK2 may serve the activity of oncogenes, similar to BCR-ABL and c-MYC, control the activation of critical signaling cascades, such as NF-κB (nuclear factor-κB), STAT3 (signal transducer and activator of transcription 3) and PTEN/PI3K/AKT (phosphatase and tensin homolog protein/phosphoinositide 3-kinase/AKR thymoma), and sustain multiple cellular stress-elicited pathways, such as the proteotoxic stress, unfolded protein and DNA-damage responses. CK2 has also been shown to have an essential role in tuning signals derived from the stromal tumor microenvironment. Not surprisingly, targeting CK2 in lymphoid tumor cell lines or mouse xenograft models can boost the cytotoxic effects of both conventional chemotherapeutics and novel agents, similar to heat-shock protein 90, proteasome and tyrosine kinases inhibitors. In this review, we summarize the evidence indicating how CK2 embodies most of the features of a cancer growth-promoting non-oncogene, focusing on lymphoid tumors. We further discuss the preclinical data of the use of small ATP-competitive CK2 inhibitors, which hold the promise to be additional options in novel drug combinations for the therapy of lymphoid and plasmacellular malignancies.

Guanylate cyclase activity in Escherichia coli mutants defective in adenylate cyclase.

Guanylate cyclase, which catalyzes the synthesis of guanosine 3',5'-monophosphate, has been assayed in several strains of Escherichia coli. They include wild-type cells and mutants defective in adenylate cyclase, which is responsible for the synthesis of adenosine 3',5'-phosphate. Our results demonstrate that adenylate cyclase and guanylate cyclase are two different enzymes in E. coli and suggest that the gene that encodes adenylate cyclase also plays a regulatory role in the synthesis of guanylate cyclase.

Cyclic nucleotide metabolism in differentiated and undifferentiated epithelial thyroid cells in culture.

A highly differentiated thyroid cell line (FR-RL) was compared with a less differentiated (FR-T Cl1) and an undifferentiated (1-5G) cell line. FR-TL is modulated in vivo and in vitro by thyrotropin and has the lowest adenylate cyclase and guanylate cyclase and the highest phosphodiesterase activities. In contrast, 1-5G tumor cells do not respond to thyrotropin and have the highest adenylate cyclase guanylate cyclase and lowest hydrolyzing enzyme activities. Intermediate enzyme activities were found in FR-T Cl1 cells. The differences between the two normal rat thyroid cell lines are not due to differences in the composition of the growth medium.

The adenylate cyclase-cyclic AMP-phosphodiesterase system in pathological human thyroid.

The adenylate cyclase-cyclic AMP-phosphodiesterase system of human thyroid tissues adjacent to cold nodules (control), two follicular adenomas, one hyperplastic thyroid and one hyperfunctioning follicular carcinoma have been compared. In the hyperfunctional follicular carcinoma the basal adenylate cyclase is much higher than in control tissue, carcinoma adenylate cyclase does not respond to TSH and prostaglandin E1, whereas it responds normally to fluoride. In the hyperplastic, but hypofunctional thyroid the basal adenylate cyclase is higher than in normal tissue whereas the response to TSH, PGE1, and fluoride is normal. No difference between the follicular adenomas and normal thyroid stimulated and unstimulated adenylate cyclase was observed. Furthermore in various thyroid tissues no changes in the level of cyclic AMP phosphodiesterase was found. Our data indicate a greater change in the synthesis rather than in degradation of cyclic AMP in the human pathological thyroids studied.

Diminished binding of thyroid-stimulating hormone in a transplantable rat thyroid tumor as a possible cause of hormone unresponsiveness.

The adenylate cyclase activity and the binding of 125I-labeled thyroid-stimulating hormone (TSH) of normal and tumor rat thyroid plasma membranes were compared. No significant difference in the basal and fluoride-sensitive adenylate cyclase activity between normal and tumor plasma membranes was observed. Thyroid plasma membranes responded to TSH, whereas the enzyme from the tumor plasma membranes was TSH insensitive. Thyroid plasma membranes boud 125I-TSH. Tumor plasma membranes bound 125I-TSH poorly. At the highest concentration of unlabeled TSH used, 80% of the 125I-TSH that was bound to thyroid plasma membranes was displaced, whereas only 10% of the 125I-TSH bound to tumor plasma membranes was displaced. Therefore, it seems likely that the failure of this tumor to respond to TSH is due to an alteration in the functional unit of membrane adenylate cyclase at the level of the receptor subunit.