cx-4945 and Carcinogenesis

Endothelin-1 is a mitogenic peptide that activates several proliferation, survival, and invasiveness pathways. The effects of endothelin-1 rely on its activation by endothelin-converting enzyme-1 (ECE1), which is expressed as four isoforms with different cytoplasmic N termini. Recently, isoform ECE1c has been suggested to have a role in cancer aggressiveness. The N terminus of ECE1c is phosphorylated by protein kinase CK2 (also known as casein kinase 2), and this enhances its stability and promotes invasiveness in colorectal cancer cells. However, it is not known how phosphorylation improves stability and why this is correlated with increased aggressiveness. We hypothesized that CK2 phosphorylation protects ECE1c from N-terminal ubiquitination and, consequently, from proteasomal degradation. Here, we show that lysine 6 is the bona fide residue involved in ubiquitination of ECE1c and its mutation to arginine (ECE1c

Topics: Animals; Carcinogenesis; Casein Kinase II; Cell Line, Tumor; Colorectal Neoplasms; Endothelin-Converting Enzymes; Female; Gene Expression Regulation, Neoplastic; Humans; Immunohistochemistry; Mice; Mice, Inbred BALB C; Mice, Inbred NOD; Mice, SCID; Mutation; Naphthyridines; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplastic Stem Cells; Phenazines; Phosphorylation; Prognosis; Protein Stability; Recombinant Proteins; Up-Regulation; Xenograft Model Antitumor Assays

Casein kinase 2 (CK2) has become a potential therapeutic target in gastric cancer; however, the underlying mechanism remains incompletely understood. TAp73, a structural homolog of the tumor suppressor p53, acts as a critical regulator of the Warburg effect. Recent study reveals that aberrant CK2 signaling is able to inhibit TAp73 function. Here we determine that TAp73 is overexpressed in AGS-1 but not in SNU-5 gastric cancer cell line as compared with normal gastric cells. In addition, we show that TAp73 expression is required for the maintenance of glucose uptake and lactate release in AGS-1 but not in SNU-5 gastric cancer cells. Importantly, the use of CX-4945, a selective inhibitor of protein kinase CK2, inhibits cell growth and invasion, and promotes cell apoptosis in AGS-1 with decreased TAp73 expression as well as downregulated glucose uptake and lactate release. Although TAp73 knockdown resulted in significant decreases in TAp73 expressions in SNU-5 cell line, no differences in glucose uptake and lactate release were observed between SNU-5 and normal gastric cells. Moreover, TAp73 gene overexpression promotes glucose uptake and lactate release and abolishes the anti-cancer effects of CX-4945 in gastric cancer cell line AGS-1. The impacts of CX-4945 on glycolysis and tumorigenesis were strongly limited in SNU-5 gastric cancer cell line. These findings suggest that CX-4945 elicits an anti-Warburg effects in gastric cancer overexpressing Tap73 and inhibits gastric tumorigenesis.

Topics: Anticarcinogenic Agents; Carcinogenesis; Casein Kinase II; Cell Line, Tumor; Down-Regulation; Humans; Naphthyridines; Phenazines; Protein Kinase Inhibitors; Stomach Neoplasms; Tumor Protein p73; Warburg Effect, Oncologic

Protein kinase CK2 is a highly conserved and constitutively active Ser/Thr-kinase that phosphorylates a large number of substrates, resulting in increased cell proliferation and survival. A known target of CK2 is Akt, a player in the PI3K/Akt/mTORC1 signaling pathway, which is aberrantly activated in 32% of colorectal cancer (CRC) patients. On the other hand, mTORC1 plays an important role in the regulation of protein synthesis, cell growth, and autophagy. Some studies suggest that CK2 regulates mTORC1 in several cancers. The most recently developed CK2 inhibitor, silmitasertib (formerly CX-4945), has been tested in phase I/II trials for cholangiocarcinoma and multiple myeloma. This drug has been shown to induce autophagy and enhance apoptosis in pancreatic cancer cells and to promote apoptosis in non-small cell lung cancer cells. Nevertheless, it has not been tested in studies for CRC patients. We show in this work that inhibition of CK2 with silmitasertib decreases in vitro tumorigenesis of CRC cells in response to G2/M arrest, which correlates with mTORC1 inhibition and formation of large cytoplasmic vacuoles. Notably, molecular markers indicate that these vacuoles derive from massive macropinocytosis. Altogether, these findings suggest that an aberrantly elevated expression/activity of CK2 may play a key role in CRC, promoting cell viability and proliferation in untreated cells, however, its inhibition with silmitasertib promotes methuosis-like cell death associated to massive catastrophic vacuolization, accounting for decreased tumorigenicity at later times. These characteristics of silmitasertib support a potential therapeutic use in CRC patients and probably other CK2-dependent cancers.

Topics: Carcinogenesis; Casein Kinase II; Cell Cycle Checkpoints; Cell Death; Cell Movement; Cell Survival; Colorectal Neoplasms; HCT116 Cells; HT29 Cells; Humans; Naphthyridines; Phenazines; Pinocytosis; Protein Kinase Inhibitors; Transfection; Vacuoles