Selenium sensitizes MCF-7 breast cancer cells to doxorubicin-induced apoptosis through modulation of phospho-Akt and its downstream substrates.
Doxorubicin is an effective drug against breast cancer. However, the favorable therapeutic response to doxorubicin is often associated with severe toxicity. The present research was aimed at developing a strategy of increasing doxorubicin sensitivity so that lower doses may be used without compromising efficacy. The MCF-7 human breast cancer cell line currently in use in our laboratory did not respond to doxorubicin cell killing during a 24-h treatment period. By combining doxorubicin with selenium, we were successful in producing a brisk enhancement of apoptosis. We examined the effects of these two agents on Akt activation and found that selenium was capable of depressing doxorubicin-induced Akt phosphorylation. Several lines of evidence converged to support the notion that this effect is important in mediating the synergy between selenium and doxorubicin. Selenium was no longer able to sensitize cells to doxorubicin under a condition in which Akt was constitutively activated. Increased Akt phosphorylation following treatment with doxorubicin was accompanied by increased phosphorylation of glycogen synthase kinase 3beta (GSK3beta) and FOXO3A, which are substrates of Akt (both GSK3beta and FOXO3A lose their proapoptotic activities when they are phosphorylated). Selenium reduced the abundance of phospho-GSK3beta induced by doxorubicin, whereas chemical inhibition of GSK3beta activity muted the apoptotic response to the selenium/doxorubicin combination. Additional experiments showed that selenium increased the transactivation activity of FOXO3A, as evidenced by a reporter gene assay, as well as by the elevated expression of Bim (a target gene of FOXO3A). The functional significance of Bim was confirmed by the observation that RNA interference of Bim markedly reduced the potency of selenium/doxorubicin to induce apoptosis.
Li
Song
S
Department of Cancer Chemoprevention, Roswell Park Cancer Institute, Elm and Carlton Streets, Buffalo, NY 14263, USA.
Zhou
Yunfei
Y
Wang
Ruiwen
R
Zhang
Haitao
H
Dong
Yan
Y
Ip
Clement
C
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000037:antagonists & inhibitors / Q000378:metabolism; D020868:Gene Silencing; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D012643:Selenium / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D014407:Tumor Cells, Cultured
D000903:Antibiotics, Antineoplastic; D000975:Antioxidants; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; C499517:FOXO3 protein, human; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D004317:Doxorubicin; D011065:Poly(ADP-ribose) Polymerases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D012643:Selenium