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Background/Aims: Accumulating evidence has suggested that free fatty acids (FFAs) interact with protein kinases and protein phosphatases. The present study examined the effect of FFAs on protein phosphatases and Akt. Methods: Activities of protein phosphatase 1 (PP1), protein phosphatase 2A (PP2A), and protein tyrosine phosphatase 1B (PTP1B) were assayed under the cell-free conditions. Phosphorylation of Akt was monitored in MSTO-211H human malignant pleural mesothelioma cells without and with knocking-down phosphatidylinositol 3 kinase (PI3K) or 3-phosphoinositide-dependent protein kinase-1 (PDK1). Results: In the cell-free assay, unsaturated FFAs (uFFAs) such as oleic, linoleic and linolenic acid and saturated FFAs (sFFAs) such as stearic, palmitic, myristic, and behenic acid markedly reduced PTP1B activity, with the potential for uFFAs greater than that for sFFAs. All the investigated sFFAs inhibited PP2A activity, but otherwise no inhibition was obtained with uFFAs. Both uFFAs and sFFAs had no effect on PP1 activity. Oleic acid phosphorylated Akt both on Thr308 and Ser473, while stearic acid phosphorylated Akt on Thr308 alone. The effects of oleic and stearic acid on Akt phosphorylation were abrogated by the PI3K inhibitor wortmannin or the PDK1 inhibitor BX912 and also by knocking-down PI3K or PDK1. Conclusion: The results of the present study indicate that uFFAs and sFFAs could activate Akt through a pathway along a PI3K/PDK1/Akt axis in association with PTP1B inhibition.

Background/Aims: Our earlier studies suggested crosstalk between IRS/PI3 kinase/PDK1/Akt/Rac1/ROCK and (Shc2/Grb2/SOS)/Ras/Raf/MEK/ERK pathways downstream PDGF-ββ receptor responsible for chemotaxis and proliferation of malignant mesothelioma cells. The present study was conducted to obtain evidence for this. Methods: To assess activation of Akt, MEK, and ERK, Western blotting was carried out on MSTO-211H malignant mesothelioma cells using antibodies against phospho-Thr308-Akt, phopho-Ser473-Akt, Akt, phospho-MEK, MEK, phopho-ERK1/2, and ERK1/2. To knock-down Akt, PI3 kinase, PDK1, and Rac1, siRNAs silencing each-targeted gene were constructed and transfected into cells. To monitor Rac1 activity, FRET monitoring was carried out on living and fixed cells. Results: ERK was activated under the basal conditions in MSTO-211H cells, and the activation was prevented by inhibitors for PI3 kinase, PDK1, Akt, and Rac1 or by knocking-down PI3 kinase, PDK1, Akt, and Rac1. Akt was also activated under the basal conditions, and the activation was suppressed by a MEK inhibitor and an ERK1/2 inhibitor. In the FRET analysis, Rac1 was activated under the basal conditions, and the activation was inhibited by a MEK inhibitor and an ERK1/2 inhibitor. Conclusion: The results of the present study show that ERK could be activated by PI3 kinase, PDK1, Akt, and Rac1 and that alternatively, Akt and Rac1 could be activated by MEK and ERK in MSTO-211H cells.

Two patients (one male and one female) with bronchial asthma were diagnosed as having eosinophilic gastroenteritis (EG). The condition was revealed by biopsies through fibrescopic endoscopy. According to the Klein classification, they had mucosal disease. The symptoms were abdominal pain and nausea. The symptoms subsided with corticosteroid administration in one patient and with palliative treatment in the other patient. It was suggested that fibrescopic endoscopy biopsy is needed to identify coexisting EG if a bronchial asthma patient complains of severe gastrointestinal symptoms.