Mechanisms of drug-resistance and apoptosis in oral carcinoma cells

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We examined the effects of anticancer drugs on induction of apoptosis and the transcriptional regulation of the multidrug resistance-1 (MDR1) gene in' oral squamous carcinoma cells. SCCKN cells were shown to be highly sensitive to various anticancer drugs, whereas SCCTF cells were minimally sensitive to these reagents. Peplomycin induced apoptosis in both SCCKN and SCCTF Cells in a dose-dependent fashion with the maximal effect at concentrations of 1 μM and 10 μM, respectively. Apoptosis was induced in SCCKN cells treated with 1 μM peplomycin, but not in SCCTF cells. RT-PCR revealed that MDR1 mRNA was highly expressed in SCCTF cells while it was under the limit of detection in SCCKN cells. After treatment with Hoechst 33342 to assess efflux action of MDR1 protein, intense staining occurred in SCCKN cells, whereas the staining was very weak in SCCTF cells. With an electrophoretic mobility shift assay using the MDR1 promoter region, a DNA-protein. Protein phosphorylation and dephosphorylation has been recognized as a key mechanism in cell function. Nucleolin is an abundantly expressed nucleolar phosphoprotein and is located mainly in the nucleolus. The staining pattern of nucleolin in cultured cells is similar to that of PP 1δ. Nucleolin was demonstrated to bind to PP1δ in nucleolus by using immunocytochemical and immunoprecipitation. methods. A major band, 110 kDa, was detected in the proteins obtained from the control cells. The level of the 110 kDa protein decreased in the apoptotic cells, whereas an additional band, 80 kDa, appeared and the level of this protein increased in the proteins prepared from okadaic acid-induced apoptotic cells. Our results indicate that PP1δ directly binds to nucleolin in the nucleolus and that nucleolin is cleaved during apoptosis.