Apigenin manipulates the ubiquitin–proteasome system to rescue estrogen receptor-β from degradation and induce apoptosis in prostate cancer cells
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To investigate apigenin (5,7,4-trihydroxyflavone), a dietary flavonoid with proteasome-inhibitory activity (desired for the management of multiple types of cancers), against FDA-approved anticancer proteasome inhibitor bortezomib in context to its effects on the tumor suppressor estrogen receptor-beta (ER-β) in prostate cancer cells.
Prostate cancer (PC-3) cells were treated with either apigenin or bortezomib, and proliferation inhibition was correlated with proteasomal biochemistry, ER-degradation and cell apoptosis.
Apigenin specifically inhibited only chymotrypsin-like activity of proteasome without affecting trypsin and caspase-like activities, which was in contrast to the non-specific inhibition of all the three activities by bortezomib. Apigenin selectively increased the protein levels of ER-β at 1.8 and 10.0 µM (without affecting mRNA levels) and preferentially accumulated ubiquitinated ER-β over ER-α in PC-3. Apigenin-treated cells exhibited increased ER-β interactions with ubiquitin-protein ligase E6AP, downregulated PSMA5 (α-5 subunit for assembly of 20S proteasome) without affecting PSMB1 (β-1 subunit), PSMB2 (β-2 subunit) and PSMB5 (β-5 subunit, whose overexpression by bortezomib causes drug resistance) of proteasome at mRNA levels. Caspase-3 activation in PC-3 by apigenin was dependent on caspase-8 activity but independent of mitochondrial membrane depolarization. The deubiquitinase USP14 activity, which antagonizes degradation of proteins via proteasome, was significantly increased by apigenin treatment.
Apigenin selectively inhibits proteasomal degradation of tumor suppressor ER-β by specifically inhibiting chymotrypsin-like activity of proteasome, preventing its assembly via PSMA5 and inhibiting USP14 enzyme activity in prostate cancer cells, resulting in cancer cell apoptosis. Unlike bortezomib, apigenin’s actions are subtle, precise, mechanistically distinct and capable of abstaining drug resistance.
KeywordsApigenin Proteasome Ubiquitination Estrogen receptor-beta Bortezomib Prostate cancer
This study was supported by a grant from the Ministry of Health and Family Welfare, Government of India (GAP0001). [CDRI communication number 8844]
Conflict of interest
- 1.Globocan (2008) Cancer incidence and mortality worldwide. http://www.iarc.fr/en/media-centre/iarcnews/2010/globocan2008.php. Accessed 16 Nov 2014
- 15.Horvath LG, Henshall SM, Lee CS, Head DR, Quinn DI, Makela S, Delprado W, Golovsky D, Brenner PC, O’Neill G, Kooner R, Stricker PD, Grygiel JJ, Gustafsson JA, Sutherland RL (2001) Frequent loss of estrogen receptor-beta expression in prostate cancer. Cancer Res 61:5331–5335Google Scholar
- 18.Harlow E, Lane D (2006) Bradford assay. CSH Protoc. doi: 10.1101/pdb.prot4644
- 20.Kisselev AF, Garcia-Calvo M, Overkleeft HS, Peterson E, Pennington MW, Ploegh HL, Thornberry NA, Goldberg AL (2003) The caspase-like sites of proteasomes, their substrate specificity, new inhibitors and substrates, and allosteric interactions with the trypsin-like sites. J Biol Chem 278:35869–35877CrossRefGoogle Scholar
- 23.Lau KM, LaSpina M, Long J, Ho SM (2000) Expression of estrogen receptor (ER)-alpha and ER-beta in normal and malignant prostatic epithelial cells: regulation by methylation and involvement in growth regulation. Cancer Res 60:3175–3182Google Scholar
- 24.Picard N, Charbonneau C, Sanchez M, Licznar A, Busson M, Lazennec G, Tremblay A (2008) Phosphorylation of activation function-1 regulates proteasome-dependent nuclear mobility and E6-associated protein ubiquitin ligase recruitment to the estrogen receptor beta. Mol Endocrinol 22:317–330CrossRefGoogle Scholar
- 32.Arlt A, Bauer I, Schafmayer C, Tepel J, Muerkoster SS, Brosch M, Roder C, Kalthoff H, Hampe J, Moyer MP, Folsch UR, Schafer H (2009) Increased proteasome subunit protein expression and proteasome activity in colon cancer relate to an enhanced activation of nuclear factor E2-related factor 2 (Nrf2). Oncogene 28:3983–3996CrossRefGoogle Scholar
- 33.Sacco JJ, Coulson JM, Clague MJ, Urbe S (2010) Emerging roles of deubiquitinases in cancer-associated pathways. IUBMB Life 62:140–157Google Scholar