Cancer Research and Treatment

Changes of Telomerase Activity by Protein Kinase C Modulators in Human Ovarian Cancer Cell Lines: Soo Young Hur, Joon Mo Lee, Sung Eun Namkoong, Jin Woo Kim; J Korean Cancer Assoc. 2000;32(4):724-733.

Abstract PDF: PURPOSE
This study was designed to find out whether protein kinase C (PKC) may affect telomerase activity in human ovarian cancers.
MATERIALS AND METHODS
To determine whether PKC modulators influence PKC activities, NIH: OVCAR-3 and CUMO-2, cells were treated with PKC inhibitors, G 6976 and bisindolyl maleimide I, and PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA). Telomerase acti vity was determined by telomeric repeat amplification protocol (TRAP). Analysis of the expres sion of each telomerase subunits, human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT), was performed by RT-PCR. We also examined the alternative splicing of hTERT.
RESULTS
G 6976 and bisindolylmaleimide I inhibited PKC activity. Telomerase activities appeared to be affected in a time-dependent manner by these two PKC inhibitors. PKC activities were increased in parallel with telomerase activity by TPA at the low dose (10 nM), but their activities were down-regulated at the high dose (1 micrometer). RT-PCR demonstrated the presence of hTR and hTERT mRNA before and after the treatment of PKC modulators, respectively, and showed the presence of one alternatively spliced transcript and full-length hTERT transcripts.
CONCLUSION
These results showed that telomerase activity was affected by PKC and suggested PKC modulation may serve as an useful tool in the regulation of telomerase activity.

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Phorbol Ester Induced - Apoptosis Mediated by Activating Serine Protease ( s ) and Caspase - 3 / CPP32 in SNU - 16 Human Gastric Cancer Cell Line: I C Park, M J Park, T B Choe, J J Jang, S I Hong, S H Lee; J Korean Cancer Assoc. 2000;32(2):270-278.

Abstract PDF: PURPOSE
Protein kinase C (PKC) is a family of phospholipid dependent serine/threonine protein kinases that have important role in differentiation, development and tumor promotion. PKC also has been reported to be implicated in the induction of apoptosis in a number of studies, but the efforts to define a role for PKC in the induction of apoptosis have been complicated by conflicting reports.
MATERIALS AND METHODS
To determine the effect of phorbol 12-myristate 13-acetate (PMA) on the induction of apoptosis, DNA fragmentation was detected by agarose gel electrophoresis and morphological changes of apoptotic cells were detected by Hoechst 33258 staining. For the detection of caspase-3/CPP32 activity, we used the enzyme substrate Ac-DEVD-pNa and anti- D4-GDI antibody.
RESULTS
In the present study, PMA, a PKC activator, induced apoptosis in SNU-16 human gastric cancer cell line, whose apoptosis was significantly inhibited by the PKC inhibitor, chelerythrine chloride. The caspase-3/CPP32 protease activity was increased in PMA-induced apoptosis. Furthermore, 4-(2-aminoethyl) benzenesulfonyl fluoride (AEBSF), a serine profease inhibitor, also significantly suppressed PMA-induced cell death in an upstream of caspase-3/CPP32.
CONCLUSION
These findings indicate that PMA induces apoptotic cell death in the SNU-16 adenocarcinoma cells through PKC activation, which activates AEBSF-sensitive serine proteases and caspase-3/CPP32. Therefore, our results suggest that PKC would be a potential target for induction of apoptosis.

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Induction of Differentiation of Leukemic Cells in Vitro: Mi Jeong Lee; J Korean Cancer Assoc. 1990;22(3):367-374.

Abstract PDF: Appropriately stimulated, leukemic cells can be made to differentiate suggesting new approaches to cancdr treatment. We tried various inducers to leukemic cell lines, Ml originated from mouse myeloid leukemia and U 937 originated from human histiocytic lymphoma. Induction of differentia- tion was initiated by adding cyclosporin A(CSA), bacterial lipopolysaccharide (LPS), retinoic acid (RA) and phorbol l2-mvristate 13-acetate(PMA) to M1 and U-937 cells growing in defined mediunm. Cell growth and differentiation markers such as reduction of nitro blue tetrazolium(NBT) dye, Fc receptor expression and cell adhesion were observed. CSA and LPS stimulated differentiation and growth inhibition of Ml cells. RA and PMA stimulated differentiation and growth inhibition of U-937 cells. Tamoxifen (TMF), protein kinase C (PKC) inhibitor, inhibited the differentiation of U-937 cells induced to differentiate by PMA. This result suggests that PKC is an important enzyme in the differentiation of U-937 cells.

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Reversal of ( MDR ) Multidrug resistance ) in Adiamycin - Resistant MCF - 7 Cells by Tamoxifen : Possible Role of Protedin Kinase ( PCK ): Han Lim Moon, Hoon Kyo Kim, Kyung Shik Lee; J Korean Cancer Assoc. 1994;26(2):242-249.

Abstract PDF: Introduction: MDR(multidrug resistance), which is caused by mdr gene and its product, p-gly- coprotein, is one of the most important obstacles during cancer chemtherapy. Recently, many efforts to reverse MDR have been done and partly applied in clinic. Verapamil, quinidine, dipyridamole and cyclosporine were the representative ones and tamoxifen and toremifene have been known as those kinds. On the other hand, protein kinase c(PKC) has a critical role in cell proliferation and differentiation and also associated with MDR. Using wild type and adriamycin-resistant type of MCF-7(MCF-7/WT and MCF-7/ADM), we found antiestrogen, tamoxifen, had a synergistic cytotoxic effect with adriamycin on MCF-7/ADM, not on MCF-1/ WT. We also tried to clarify the mechanisms of synergism of tamoxifen with adriamycin, espe- cially in the viewpoint of drug uptake and PKC activity. Results: IC of adriamycin-cytotoxicity on MCF-7/WT and MCF-7/ADM was 0.2 ug/ml and 2 ug/ml, respectively. Tamoxifen moved IC of adriamycin-cytotoxicity of left in a dose-dependent manner in MCF-7/ADM, and 10 pM concentration of tamoxifen made IC 0.2 pg/ml in that cell line, which was very similar to IC in MCF-7/WT. But tamoxifen did not have synergistic cytotoxicity with adriamycin on MCF-7/WT. In drug efflux study with C14-adriamycin, tamoxifen enhanced drug uptake more than 200% in MCF-7/ADM although it markedly decreased when tamoxifen was added. There was no difference in baseline PKC activity and degree of dose-dependent inhibition on PKC activity by adriamycin in those two cell lines. Canclusion; Tamoxifen is thought to be as one of the plausible agents to reverse MDR in breast cancer. The possible mechanisms are to increase cellular uptake of adriamycin and to inhibit PKC activity.

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