okadaic-acid and Colorectal-Neoplasms

The tumor suppressor protein phosphatase 2A (PP2A) is frequently inactivated in human cancer and phosphorylation of its catalytic subunit (p-PP2A-C) at tyrosine-307 (Y307) has been described to inhibit this phosphatase. However, its molecular and clinical relevance in colorectal cancer (CRC) remains unclear.. p-PP2A-C Y307 was determined by immunoblotting in 7 CRC cell lines and 35 CRC patients. CRC cells were treated with the PP2A activator forskolin alone or combined with the PP2A inhibitor okadaic acid, 5-fluorouracil and oxaliplatin. We examined cell growth, colonosphere formation, caspase activity and AKT and ERK activation.. PP2A-C was found hyperphosphorylated in CRC cell lines. Forskolin dephosphorylated and activated PP2A, impairing proliferation and colonosphere formation, and inducing activation of caspase 3/7 and changes in AKT and ERK phosphorylation. Moreover, forskolin showed additive effects with 5-fluorouracil and oxaliplatin treatments. Analysis of p-PP2A-C Y307 in primary tumors confirmed the presence of this alteration in a subgroup of CRC patients.. Our data show that PP2A-C hyperphosphorylation is a frequent event that contributes to PP2A inhibition in CRC. Antitumoral effects of forskolin-mediated PP2A activation suggest that the analysis of p-PP2A-C Y307 status could be used to identify a subgroup of patients who would benefit from treatments based on PP2A activators.

Topics: Aged; Aged, 80 and over; Antimetabolites, Antineoplastic; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; Cell Proliferation; Colforsin; Colorectal Neoplasms; Enzyme Inhibitors; Female; Fluorouracil; Humans; Immunoenzyme Techniques; Male; Middle Aged; Okadaic Acid; Organoplatinum Compounds; Oxaliplatin; Phosphorylation; Protein Phosphatase 2; Tumor Cells, Cultured; Vasodilator Agents

In the last decades, relevant efforts have been made to reduce the cancer incidence in the European Union. The prevention programmes against cancer have obtained satisfactory results except for colorectal cancer (CRC). Identification of risk factors is primordial to plan preventive strategies for CRC. We hypothesize that shellfish consumption is increasing CRC incidence. DSP toxins, present in some seafood products, seem to behave like tumour agents. There are no relevant studies on real health-risk of consuming DSP toxins, just some experimental and ecological evidence. Preventive interventions for reducing CRC risk must be approached through the collaboration of governmental, health and environmental sectors as a single regulatory agency. Sometimes, shellfish accumulates diarrhetic shellfish poisoning (DSP) toxins (i.e. okadaic acid and its derivatives) which provoke a gastrointestinal illness (DSP syndrome). Furthermore, DSP toxins are tumour promoters that could increase CRC risk. The current regulation about level of DSP toxins in shellfish meat is only centred on reduction of the gastrointestinal symptoms. Unfortunately, legal levels of DSP toxins in shellfish are enough to increase CRC risk. A review of legislation on DSP toxins is urgent.

Topics: Animals; Carcinogens; Colorectal Neoplasms; Diet; Europe; Humans; Marine Toxins; Models, Biological; Okadaic Acid; Risk Factors; Shellfish

Butyric acid is well recognized as a histone deacetylase (HDAC) inhibitor, and changes in histone acetylation are thought to alter gene expression. The mechanism by which sodium butyrate (NaB) induces p21WAF1/CIP1, a critical gene involved in the antiproliferative effect of NaB, was studied at the chromatin level. Using chromatin immunoprecipitation (ChIP) assay, acetylation of histone H3 was observed at the proximal region of the promoter within 30 min of NaB exposure and this extended to the distal region within 2 hr. By contrast, histone H4 was acetylated both at the proximal and the distal regions of the promoter within 30 min. NaB did not influence other histone modifications. NaB stimulated recruitment of the transcription factors ZBP89 and Sp1 as well as GCN5, but did not influence recruitment of Sp3, HDAC1, p300, or CBP. As recruitment of HDAC1 to the promoter appeared not to account for NaB-induced changes in histone acetylation, we aimed to influence HDAC activity by altering its phosphorylation status. The kinase inhibitor, H7, suppressed p21WAF1/CIP1 mRNA in both the absence and the presence of NaB without influencing the butyrate-induced hyperacetylation of H3 and H4 associated with the p21WAF1/CIP1 promoter. These results suggest that acetylation of histones at the p21WAF1/CIP1 promoter is not sufficient for NaB to exert antiproliferative effects via transcription of the p21WAF1/CIP1 gene. Induction of p21WAF1/CIP1 transcription by the phosphatase inhibitor, okadaic acid, in the absence of changes in association of acetylated histones with the p21WAF1/CIP1 promoter provides further evidence of the importance of phosphorylation to p21WAF1/CIP1 transcription.

Topics: Acetylation; Adenocarcinoma; Butyrates; Cell Division; Chromatin; Colorectal Neoplasms; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Gene Expression Regulation, Neoplastic; Histones; Humans; Okadaic Acid; Phosphorylation; Precipitin Tests; RNA, Messenger; Transcription Factors; Transcription, Genetic; Transcriptional Activation; Tumor Cells, Cultured