Effects of okadaic acid on cell growth, anchorage-independent growth, and co-cultures of normal (KMS-6), immortalized (KMST-6), and neoplastically transformed (KMST-6T and KMST-6/RAS) human fibroblasts

Shellfish consumption: a major risk factor for colorectal cancer

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.

Induction of protein phosphatase type 2A in response to disruption of cell-matrix interactions

The proliferation of most cells is strictly dependent on cell-matrix interactions, a phenomenon called anchorage dependence. Because tumor cells are often independent of this regulation, it is important to characterize the molecular components that are involved in this control. We therefore investigated a possible role of serine/threonine protein phosphatases in the regulation of anchorage-dependent cell growth. We found that the activity of serine/threonine protein phosphatase type 2A (PP2A) and, to a lesser extent, that of type 1 (PP1), was upregulated in response to the disruption of cellular attachment. In the case of PP2A, this induction was due to the transcriptional activation of the gene and increased expression of its protein. The increase in phosphatase activity corresponded with a decrease in the phosphorylation of cellular proteins that occurred in anchorage-dependent cells, but to a much lesser degree in anchorage-independent cells. At the same time, the activity of cyclin-dependent kinases was downregulated in anchorage-dependent, but not in anchorage-independent cells. Thus, our results indicate that the balance of kinase and phosphatase activity in anchorage-dependent cells is tipped in favor of phosphatase activity, which seems to dominate the extent of reversible protein phosphorylations after cellular detachment. In contrast, anchorage-independent cells appear to neutralize elevated phosphatase activity through sustained, strong kinase activity.