casein-kinase-ii and Colorectal-Neoplasms

As anchoring Casein Kinase 2 (CK2) in several human tumors, DN701 as a novel CK2 inhibitor was applied to reverse chemo-resistance via its antitumor effect synergized with oxaliplatin. Recently, translesion DNA synthesis (TLS) has attracted our attention for its association with chemo-resistance, as demonstrated by previous clinical data. The in vitro cell-based properties supported that oxaliplatin combined with DN701 could reverse drug resistance via blockading CK2-mediated aryl hydrocarbon receptor (AhR) and translesion DNA synthesis (TLS)-induced DNA damage repair. Moreover, pharmacologic or genetic inhibition on REV3L (Protein reversion less 3-like) greatly impaired TLS-induced genomic instability. Mechanistically, combination of oxaliplatin with DN701 was found to inhibit CK2 expression and AhR-TLS-REV3L axis signaling, implying the potential decrease of genomic instability. In addition, the combination of oxaliplatin with DN701 could reduce CK2-AhR-TLS-related genomic instability, leading to potent antitumor effects in vivo. Our study presents an underlying mechanism that DN701 could attenuate tumoral chemo-resistance via decaying CK2-mediated AhR and TLS genomic instability, suggesting a potential cancer chemotherapeutic modality to prolong survival in chemo-resistant patients.

Topics: Casein Kinase II; Colorectal Neoplasms; DNA; DNA-Binding Proteins; DNA-Directed DNA Polymerase; Drug Resistance, Neoplasm; Genomic Instability; Humans; Oxaliplatin; Receptors, Aryl Hydrocarbon

Antitumor drug resistance is a major hurdle in treating patients with malignant tumors. Casein kinase 2α (CK2α) expression is highly enhanced in oxaliplatin-resistant CRC cells. We investigated whether CK2α expression is associated with oxaliplatin resistance in CRC cells.. To determine the effect of CK2α on drug resistance in CRC, we assessed the cell viability, adenosine triphosphate-binding cassette (ABC) transporter expression, apoptosis, and sphere formation according to CK2α expression in oxaliplatin-resistant CRC cells.. CK2α expression was significantly increased in oxaliplatin-resistant CRC cells compared with that in wild-type CRC cells. In addition, the mRNA expression of ABC transporters, including ABCA12, ABCC2, and ABCE1, was significantly enhanced in oxaliplatin-resistant CRC cells, whereas this effect was blocked by the knockdown of CK2α. Furthermore, a cell viability test showed that oxaliplatin resistance was inhibited by decreasing CK2α expression, resulting in the induction of apoptosis and suppression of sphere formation.. CK2α regulates cell survival, apoptosis, sphere formation, and drug resistance in oxaliplatin-resistant CRC cells by regulating ABC transporters. Therefore, targeting CK2α in drug-resistant CRC cells may be a novel strategy for treating patients with CRC.

Topics: ATP-Binding Cassette Transporters; Casein Kinase II; Cell Line, Tumor; Colorectal Neoplasms; Drug Resistance, Neoplasm; Humans; Oxaliplatin

Dysregulation of Hippo pathway leads to hyperactivation of YAP-TEAD transcriptional complex in various cancers, including colorectal cancer (CRC). In this study, we observed that HHEX (Hematopoietically expressed homeobox) may enhance transcription activity of the YAP-TEAD complex. HHEX associates with and stabilizes the YAP-TEAD complex on the regulatory genomic loci to coregulate the expression of a group of YAP/TEAD target genes. Also, HHEX may indirectly regulate these target genes by controlling YAP/TAZ expression. Importantly, HHEX is required for the pro-tumorigenic effects of YAP during CRC progression. In response to serum stimulation, CK2 (Casein Kinase 2) phosphorylates HHEX and enhances its interaction with TEAD4. A CK2 inhibitor CX-4945 diminishes the interaction between HHEX and TEAD4, leading to decreased expression of YAP/TEAD target genes. CX-4945 synergizes the antitumor activity of YAP-TEAD inhibitors verteporfin and Super-TDU. Elevated expression of HHEX is correlated with hyperactivation of YAP/TEAD and associated with poor prognosis of CRC patients. Overall, our study identifies HHEX as a positive modulator of YAP/TEAD to promote colorectal tumorigenesis, providing a new therapeutic strategy for targeting YAP/TEAD in CRC.

Topics: Carcinogenesis; Casein Kinase II; Colorectal Neoplasms; DNA-Binding Proteins; Homeodomain Proteins; Humans; Muscle Proteins; TEA Domain Transcription Factors; Transcription Factors; YAP-Signaling Proteins

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

Anti-cancer drug resistance restricts the efficacy of chemotherapy in malignant tumors. Casein kinase 2α (CK2α) is highly expressed in 5-fluorouracil (5FU)-resistant colorectal cancer (CRC) cells. We hypothesized that inhibition of CK2α might reduce CRC resistance to 5FU.. To investigate the role of CK2α in 5FU-resistant CRC cells, we assessed cell viability, apoptosis, cyclin-dependent kinase 4 (CDK4) activity, cell-cycle progression, invasion, and sphere formation in 5FU-resistant CRC cells.. CK2α levels were significantly increased in 5FU-resistant CRC cells compared to those in wild-type CRC cells. During exposure to 5FU, viability, CDK4 activity, cell-cycle progression, invasion, and sphere formation were enhanced, while apoptosis was decreased in 5FU-resistant CRC cells. These effects were mediated by the inhibiting effects of CK2α on endoplasmic reticulum (ER) stress. Combination of CK2α knockdown with 5FU treatment promoted apoptosis of 5FU-resistant CRC cells by inducing ER stress.. 5FU treatment in combination with a CK2α inhibitor may exert a synergistic effect against drug-resistant cancer cells.

Topics: Antineoplastic Combined Chemotherapy Protocols; Casein Kinase II; Cell Line, Tumor; Colorectal Neoplasms; Cyclin-Dependent Kinase 4; Drug Resistance, Neoplasm; Drug Synergism; Endoplasmic Reticulum Stress; Fluorouracil; Humans; Protein Kinase Inhibitors

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

RIOK1 has recently been shown to play important roles in cancers, but its posttranslational regulation is largely unknown. Here we report that RIOK1 is methylated at K411 by SETD7 methyltransferase and that lysine-specific demethylase 1 (LSD1) reverses its methylation. The mutated RIOK1 (K411R) that cannot be methylated exhibits a longer half-life than does the methylated RIOK1. FBXO6 specifically interacts with K411-methylated RIOK1 through its FBA domain to induce RIOK1 ubiquitination. Casein kinase 2 (CK2) phosphorylates RIOK1 at T410, which stabilizes RIOK1 by antagonizing K411 methylation and impeding the recruitment of FBXO6 to RIOK1. Functional experiments demonstrate the RIOK1 methylation reduces the tumor growth and metastasis in mice model. Importantly, the protein levels of CK2 and LSD1 show an inverse correlation with FBXO6 and SETD7 expression in human colorectal cancer tissues. Together, this study highlights the importance of a RIOK1 methylation-phosphorylation switch in determining colorectal and gastric cancer development.

Topics: Animals; Antigens, Neoplasm; Casein Kinase II; Cell Line, Tumor; Colorectal Neoplasms; Disease Models, Animal; Histone Demethylases; Histone-Lysine N-Methyltransferase; Humans; Methylation; Mice; Phosphorylation; Protein Binding; Protein Processing, Post-Translational; Protein Serine-Threonine Kinases; SKP Cullin F-Box Protein Ligases; Stomach Neoplasms; Ubiquitination

We previously demonstrated that downregulation of protein kinase CKII induces cellular senescence in human colon cancer HCT116 cells. To investigate the role of microRNAs (miRNAs) in CKII downregulation during senescence, we employed computational algorithms. Four miRNAs (miR-186, miR-216b, miR-337-3p, and miR-760) were predicted to be miRNAs against CKIIα mRNA. Mimics of all four miRNAs jointly downregulated CKIIα expression in HCT116 cells. Reporter analysis and RT-PCR have suggested that these four miRNAs may stimulate degradation of CKIIα mRNA by targeting its 3' untranslated regions (UTRs). The four miRNA mimics increased senescent-associated β-galactosidase (SA-β-gal) staining, p53 and p21(Cip1/WAF1) expression, and reactive oxygen species (ROS) production. In contrast, concomitant knockdown of the four miRNAs by antisense inhibitors increased the CKIIα protein level and suppressed CKII inhibition-mediated senescence. Finally, CKIIα overexpression antagonized senescence induced by the four miRNA mimics. Therefore, the present results show that miR-186, miR-216b, miR-337-3p, and miR-760 cooperatively promote cellular senescence through the p53-p21(Cip1/WAF1) pathway by CKII downregulation-mediated ROS production in HCT116 cells.

Topics: 3' Untranslated Regions; beta-Galactosidase; Casein Kinase II; Cellular Senescence; Colorectal Neoplasms; Cyclin-Dependent Kinase Inhibitor p21; Gene Knockdown Techniques; HCT116 Cells; Humans; MicroRNAs; Reactive Oxygen Species; Tumor Suppressor Protein p53

Colorectal cancer (CRC) is one of the most common malignancies but the current therapeutic approaches for advanced CRC are less efficient. Thus, novel therapeutic approaches are badly needed. The purpose of this study is to investigate the involvement of nuclear protein kinase CK2 α subunit (CK2α) in tumor progression, and in the prognosis of human CRC.. Expression levels of nuclear CK2α were analyzed in 245 colorectal tissues from patients with CRC by immunohistochemistry, quantitative real-time PCR and Western blot. We correlated the expression levels with clinicopathologic parameters and prognosis in human CRC patients. Overexpression of nuclear CK2α was significantly correlated with depth of invasion, nodal status, American Joint Committee on Cancer (AJCC) staging, degree of differentiation, and perineural invasion. Patients with high expression levels of nuclear CK2α had a significantly poorer overall survival rate compared with patients with low expression levels of nuclear CK2α. In multi-variate Cox regression analysis, overexpression of nuclear CK2α was proven to be an independent prognostic marker for CRC. In addition, DLD-1 human colon cancer cells were employed as a cellular model to study the role of CK2α on cell growth, and the expression of CK2α in DLD-1 cells was inhibited by using siRNA technology. The data indicated that CK2α-specific siRNA treatment resulted in growth inhibition.. Taken together, overexpression of nuclear CK2α can be a useful marker for predicting the outcome of patients with CRC.

Topics: Adult; Aged; Aged, 80 and over; Biomarkers, Tumor; Carcinoma; Casein Kinase II; Catalytic Domain; Cell Nucleus; Colorectal Neoplasms; Female; Follow-Up Studies; Gene Expression Regulation, Neoplastic; Humans; Male; Middle Aged; Nuclear Proteins; Prognosis; Young Adult

To investigate the expression of casein kinase 2β (ck2β) in colorectal cancer in relation to the metastatic ability of the cancer cells.. The expression of ck2β in 46 normal colorectal mucosa, 20 colorectal adenomas and 66 colorectal cancers were detected immunohistochemically. In colorectal cancer cells, Ck2β protein expression was knockdown by RNA interference using ck2β-specific small interfering RNA (siRNA) and the interference efficiency was assessed by Western blotting. The effect of ck2β gene knockdown on the proliferation of the colorectal cancer cells was tested with colony formation assay, and the changes in the invasive ability of the cells were observed using Transwell chamber assay.. Negative or weak ck2β expression was detected in normal colorectal mucosa, with nuclear positivity in 8.7% and cytoplasmic positivity in 13.0% of the cases. Colorectal adenomas showed moderate ck2β expression, with 60% cases showing positivity in the cell nuclei and 40% in the cytoplasm. In colorectal cancers, significantly stronger expression of ck2β was found than that in colorectal adenomas and normal colorectal mucosa (P<0.05), and 75.8% cases showed positivity in the cell nuclei and 62.1% showed cytoplasmic positivity; the expression of ck2β protein in colorectal cancers with lymph node metastasis was even higher (P<0.05). Ck2β knockdown obviously inhibited the proliferation and invasiveness of colorectal cancer cells in vitro.. The high expression of ck2β in colorectal cancer is closely correlated to the carcinogenesis and metastasis of the tumor.

Topics: Adult; Aged; Casein Kinase II; Cell Proliferation; Cell Transformation, Neoplastic; Colorectal Neoplasms; Female; Humans; Intestinal Mucosa; Male; Middle Aged; Tumor Cells, Cultured; Young Adult

Protein kinase CK2 is a highly conserved, ubiquitous protein serine/threonine kinase that phosphorylates many substrates and has a global role in numerous biological and pathological processes. Overexpression of the protein kinase CK2α subunit (CK2α) has been associated with the malignant transformation of several tissues, with not nearly as much focus on the role of CK2α in colorectal cancer (CRC). The aims of this study are to investigate the function and regulatory mechanism of CK2α in CRC development.. Expression levels of CK2α were analyzed in 144 patients (104 with CRC and 40 with colorectal adenoma) by immunohistochemistry. Proliferation, senescence, motility and invasion assays as well as immunofluorescence staining and western blots were performed to assess the effect of CK2α in CRC.. The immunohistochemical expression of nuclear CK2α was stronger in tumor tissues than in adenomas and normal colorectal tissues. Suppression of CK2α by small-interfering RNA or the CK2α activity inhibitor emodin inhibited proliferation of CRC cells, caused G0/G1 phase arrest, induced cell senescence, elevated the expression of p53/p21 and decreased the expression of C-myc. We also found that knockdown of CK2α suppressed cell motility and invasion. Significantly, CK2α inhibition resulted in β-catenin transactivation, decreased the expression levels of vimentin and the transcription factors snail1 and smad2/3, and increased the expression of E-cadherin, suggesting that CK2α regulates the epithelial-mesenchymal transition (EMT) process in cancer cells.. Our results indicate that CK2α plays an essential role in the development of CRC, and inhibition of CK2α may serve as a promising therapeutic strategy for human CRC.

Topics: Aged; beta Catenin; Cadherins; Casein Kinase II; Cell Line, Tumor; Cell Movement; Cell Nucleus; Cell Proliferation; Cellular Senescence; Colorectal Neoplasms; Epithelial-Mesenchymal Transition; Female; Gene Expression Regulation, Neoplastic; Gene Knockdown Techniques; Humans; Immunohistochemistry; Male; Middle Aged; Neoplasm Invasiveness; Protein Kinase Inhibitors; Protein Transport; Transcription Factors; Vimentin

Numerous studies have shown that platinum compounds stimulate the expression of the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase resulting in anti-proliferative activity and apoptosis. As many cancer cell types including pancreatic cancer cells express high levels of polyamines, the possibility to develop anti-tumor strategies to deplete polyamine pools has drawn considerable attention in recent years. This has been effectively accomplished by treating cells with platinum drugs in combination with polyamine analogs such as N(1),N(11)-diethylnorspermine (DENSPM). The present study, examined the cytotoxic effects of oxaliplatin in combination with stimulators of polyamine catabolism in human pancreatic cancer cells, that are notoriously resistant to chemotherapeutic treatment, and colorectal cancer cells. Additionally, as protein kinase CK2 has been shown to be an anti-apoptotic and pro-survival enzyme regulated by the intracellular polyamine pools, we aimed to investigate the effect of combined DENSPM and oxaliplatin treatment on CK2-mRNA and -protein levels. Results reported here show that treatment with oxaliplatin and DENSPM in combination impairs cell viability particularly in the case of colorectal cancer cells. The analysis of CK2 expression and activity indicates that the response to a specific treatment may depend on the impact that individual compounds exert on pro-survival and pro-death proteins at the transcription and translation levels that should be carefully evaluated in view of subsequent clinical studies.

Topics: Acetyltransferases; Antineoplastic Agents; Casein Kinase II; Cell Death; Cell Line, Tumor; Cell Proliferation; Cell Survival; Colorectal Neoplasms; Drug Synergism; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Organoplatinum Compounds; Oxaliplatin; Pancreatic Neoplasms; Polyamines; RNA, Messenger; Spermine

Elevated phospholipase D (PLD) expression prevents cell cycle arrest and apoptosis. However, the roles of PLD isoforms in cell proliferation and apoptosis are incompletely understood. Here, we investigated the physiological significance of the interaction between PLD2 and protein kinase CKII (CKII) in HCT116 human colorectal carcinoma cells. PLD2 interacted with the CKIIβ subunit in HCT116 cells. The C-terminal domain (residues 578-933) of PLD2 and the N-terminal domain of CKIIβ were necessary for interaction between the two proteins. PLD2 relocalized CKIIβ to the plasma membrane area. Overexpression of PLD2 reduced CKIIβ protein level, whereas knockdown of PLD2 led to an increase in CKIIβ expression. PLD2-induced CKIIβ reduction was mediated by ubiquitin-dependent degradation. The C-terminal domain of PLD2 was sufficient for CKIIβ degradation as the catalytic activity of PLD2 was not required. Taken together, the results indicate that the C-terminal domain of PLD2 can regulate CKII by accelerating CKIIβ degradation in HCT116 cells.

Topics: Casein Kinase II; Colorectal Neoplasms; HCT116 Cells; Humans; Phospholipase D; Protein Structure, Tertiary; RNA Interference; RNA, Small Interfering; Ubiquitin

Screening a natural compound library led to the identification of resorufin as a highly selective and potent inhibitor of protein kinase CK2. Out of 52 kinases tested, only CK2 was inhibited, in contrast to emodin, a structurally related, known CK2 inhibitor that, in addition to CK2, inhibited ten other kinases by 90%. The IC50 values determined for the CK2 holoenzymes were 1.5 mol/l and for the free catalytic subunits ca. 4 mol/l. Altogether four cell lines were subjected to resorufin and emodin treatment. In the case of the three prostate carcinoma cell lines (PC-3, DU-145, LNCaP), 24 h treatment with 40 mol/l resorufin led to 15-20% dead cells; however, no caspase-mediated apoptosis was observed. In the case of the colorectal carcinoma HCT116 cell line, a similar picture was obtained, yet, when resorufin was administered to cells treated with doxorubicin, apoptosis was strongly induced within 24 h. Endogenous protein kinase CK2 was inhibited by resorufin by ca. 80% in the three prostate cell lines. In the case of the HCT116 cells, the inhibition was only 40% supporting the notion of cell line-specific selectivity. Moreover, we analysed the effect of resorufin and emodin on selected signalling molecules in the cell lines under investigation.

Topics: Apoptosis; Casein Kinase II; Cell Line, Tumor; Colorectal Neoplasms; Emodin; Humans; Inhibitory Concentration 50; Male; Oxazines; Prostatic Neoplasms; Protein Kinase Inhibitors; Signal Transduction

The protein kinase casein kinase 2 (CK2) is a ubiquitous eukaryotic serine/threonine protein kinase that plays an important role in cell cycle progression. We find that (1) CK2 interacts with a tumor suppressor protein, adenomatous polyposis coli (APC) that occurs at the highest level in G2/M, and (2) the C-terminal region of APC, between amino acid residues 2086-2394, has the strongest activity to suppress CK2. Over-expression of this fragment in HEK293 cells or colorectal carcinoma cells that have truncated mutant APC proteins down-regulates cell proliferation rates as well as colony formation on soft agar. These results indicate that the complex formation between CK2 and full-length APC regulates CK2 activity that, in turn, regulates cell cycle progression, whereas truncated APC in colorectal carcinomas are unable to regulate the cell cycle. In the process to look for the downstream target for CK2, we found that eukaryotic translation initiation factor 5 (eIF5) is phosphorylated by CK2 in vivo as well as in vitro. These results suggest an important role of CK2 on promotion of cell growth through eIF5.

Topics: Adenomatous Polyposis Coli Protein; Amino Acid Motifs; Casein Kinase II; Cell Cycle; Cell Division; Cell Line; Cell Line, Tumor; Colorectal Neoplasms; Enzyme Activation; Eukaryotic Translation Initiation Factor 5A; Humans; Mutation; Peptide Initiation Factors; Phosphorylation; RNA-Binding Proteins

Oxidative DNA damage can generate a variety of cytotoxic DNA lesions such as 8-oxoguanine (8-oxoG), which is one of the most mutagenic bases formed from oxidation of genomic DNA because 8-oxoG can readily mispair with either cytosine or adenine. If unrepaired, further replication of A.8-oxoG mispairs results in C:G to A:T transversions, a form of genomic instability. We reported previously that repair of A.8-oxoG mispairs was defective and that 8-oxoG levels were elevated in several microsatellite stable human colorectal cancer cell lines lacking MutY mutations (human MutY homolog gene, hmyh, MYH MutY homolog protein). In this report, we provide biochemical evidence that the defective repair of A.8-oxoG may be due, at least in part, to defective phosphorylation of the MutY protein in these cell lines. In MutY-defective cell extracts, but not extracts with functional MutY, A.8-oxoG repair was increased by incubation with protein kinases A and C (PKA and PKC) and caesin kinase II. Treatment of these defective cells, but not cells with functional MutY, with phorbol-12-myristate-13-acetate also increased the cellular A.8-oxoG repair activity and decreased the elevated 8-oxoG levels. We show that MutY is serine-phosphorylated in vitro by the action of PKC and in the MutY-defective cells by phorbol-12-myristate-13-acetate but that MutY is already phosphorylated at baseline in proficient cell lines. Finally, using antibody-isolated MutY protein, we show that MutY can be directly phosphorylated by PKC that directly increases the level of MutY catalyzed A.8-oxoG repair.

Topics: Adenine; Adjuvants, Immunologic; Alleles; Amino Acid Sequence; Base Pair Mismatch; Carcinogens; Casein Kinase II; Cell Line, Tumor; Chromatography, Liquid; Colorectal Neoplasms; Cyclic AMP-Dependent Protein Kinases; Cytosine; DNA Damage; DNA Glycosylases; DNA Repair; Guanosine; Humans; Immunoblotting; Indoles; Maleimides; Microsatellite Repeats; Molecular Sequence Data; Phosphorylation; Precipitin Tests; Protein Isoforms; Protein Kinase C; Protein Serine-Threonine Kinases; Sequence Homology, Amino Acid; Serine; Software; Tetradecanoylphorbol Acetate; Up-Regulation