Protein phosphatase 2A (PP2A) has significant role in CAPE-induced apoptosis of CCRF-CEM cells via effecting human telomerase reverse transcriptase activity
Makaleler > Tam Makale · 2005
Yazarlar: Fahri ŞAHİN, C. Biray, Buket KOSOVA, Cumhur GÜNDÜZ, Nur Selvi, Hikmet Hakan AYDIN, Gülperi ÖKTEM, Nursen Topçuog̃lu, Güray SAYDAM
Cancer Research, Uluslararası, Wos, 2005, cilt 65, ss 785-785
Özet
3335 More than 70% of chemotherapeutic agents currently used for treatment of leukemia have been derived from natural sources. Complications associated with classical drugs have brought forth new researches to develop new cancer treatment agents. CAPE (caffeic acid phenethyl ester) is one of the most effective components of propolis which is collected by honey bees. The aim of this study is to investigate the cytotoxic and apoptotic effects of CAPE in CCRF-CEM cell line and to clarify the role of serin/threonine protein phosphatase 2A (PP2A) and h TERT (human telomerase reverse transcriptase) activity as an underling mechanism of CAPE-induced apoptosis. Trypan blue dye exclusion test and XTT methods were used to evaluate the cytotoxic and ELISA based on detection of oligonucleotids which can be seen during apoptosis. Acridine orange/Ethidium bromide dye technique based on detection of apoptotic bodies with fluorescent microscope were used to evaluate apoptosis. Cytotoxic effect of CAPE was detected in dose and time dependent manner with the IC 50 of 1 micromolar. ELISA and Acridine Orange/Ethidium bromide methods have shown remarkable apoptosis at 48th hour in CAPE treated cells. To investigate the role of PP2A in CAPE-induced apoptosis of CCRF-CEM cells, we performed combination studies with CAPE and Calyculin A and Okadaic acid, which are very well known inhibitors of PP2A, in IC 50 of all drugs. Combination studies revealed synergistic effect of both drugs by concomitant use. Western blot analyses of PP2A catalytic and regulatory subunits showed down regulation of expression of PP2A catalytic subunit in CAPE treated cells at 48th hour. Since PP2A is important in hTERT (telomerase catalytic subunit) activation and deactivation, we also performed hTERT activity in CAPE treated cells simultaneously. Treating cells with IC 50 of CAPE for 96 hours with the intervals of 24 hour showed marked reduction of hTERT activity. The reduction of hTERT activity in CAPE treated CCRF-CEM cells was more prominent in initial 48 hours in dose and 24 hour time dependent manner. The developed variation of hTERT activity in CAPE treated CCRF-CEM cells may be the reason of protein phosphatase interaction occured after treatment with CAPE. Apart from the familiar reasons for apoptotic effects of CAPE, protein phosphatases and hTERT activity may be crucial in CAPE- induced apoptosis and cytotoxicity of treated cell line. The results collectively suggest that the CAPE-induced decline in telomerase activity is not a consequence of CCRF-CEM cell apoptosis and that it may be caused principally by the dephosphorylation of telomerase components mediated by PP2A activation.