• Journal of Cancer Prevention
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• v.23 no.4
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• pp.153-161
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• 2018

Imbalance of protein homeostasis (proteostasis) is known to cause cellular malfunction, cell death, and diseases. Elaborate regulation of protein synthesis and degradation is one of the important processes in maintaining normal cellular functions. Protein degradation pathways in eukaryotes are largely divided into proteasome-mediated degradation and lysosome-mediated degradation. Proteasome is a multisubunit complex that selectively degrades 80% to 90% of cellular proteins. Proteasome-mediated degradation can be divided into 26S proteasome (20S proteasome + 19S regulatory particle) and free 20S proteasome degradation. In 1980, it was discovered that during ubiquitination process, wherein ubiquitin binds to a substrate protein in an ATP-dependent manner, ubiquitin acts as a degrading signal to degrade the substrate protein via proteasome. Conversely, 20S proteasome degrades the substrate protein without using ATP or ubiquitin because it recognizes the oxidized and structurally modified hydrophobic patch of the substrate protein. To date, most studies have focused on protein degradation via 26S proteasome. This review describes the 26S/20S proteasomal pathway of protein degradation and discusses the potential of proteasome as therapeutic targets for cancer treatment as well as against diseases caused by abnormalities in the proteolytic system.

• Korean Journal of Plant Resources
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• v.28 no.6
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• pp.682-689
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• 2015

Abeliophyllum distichum Nakai (A. distichum) has been reported to exert the inhibitory effect on angiotensin converting enzyme and aldose reductase. Recently, our group found that branch extracts of A. distichum (EAFAD-B) induce apoptosis through ATF3 activation in human colon cancer cells. However, anti-cancer reagents exert their activity through the regulation of various molecular targets. Therefore, the elucidation of potential mechanisms of EAFAD-B for anti-cancer activity may be necessary. To elucidate the potential mechanism of EAFAD-B for anti-cancer activity, we evaluated the regulation of cyclin D1 in human colon cancer cells. EAFAD-B decreased cellular accumulation of cyclin D1 protein. However, cyclin D1 mRNA was not changed by EAFAD-B. Inhibition of proteasomal degradation by MG132 attenuated EAFAD-B-mediated cyclin D1 downregulation and the half-life of cyclin D1 was decreased in the cells treated with EAFAD-B. In addition, EAFAD-B induced cyclin D1 phosphorylation at threonine-286 and the point mutation of threonine-286 to alanine attenuated EAFAD-B-mediated cyclin D1 proteasomal degradation. Inhibitions of both ERK1/2 by PD98059 and NF-κB by a selective inhibitor, BAY 11-7082 suppressed cyclin D1 downregulation by EAFAD-B. From these results, we suggest that EAFAD-B-mediated cyclin D1 downregulation may result from proteasomal degradation through its threonine-286 phosphorylation via ERK1/2-dependent NF-κB activation. The current study provides new mechanistic link between EAFAD-B and anti-cancer activity in human colon cancer cells.

• Molecules and Cells
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• v.39 no.11
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• pp.821-826
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• 2016

The ${\beta}$-catenin functions as an adhesion molecule and a component of the Wnt signaling pathway. In the absence of the Wnt ligand, ${\beta}$-catenin is constantly phosphorylated, which designates it for degradation by the APC complex. This process is one of the key regulatory mechanisms of ${\beta}$-catenin. The level of ${\beta}$-catenin is also controlled by the E3 ubiquitin protein ligase SIAH-1 via a phosphorylation-independent degradation pathway. Similar to ${\beta}$-catenin, STAT3 is responsible for various cellular processes, such as survival, proliferation, and differentiation. However, little is known about how these molecules work together to regulate diverse cellular processes. In this study, we investigated the regulatory relationship between STAT3 and ${\beta}$-catenin in HEK293T cells. To our knowledge, this is the first study to report that ${\beta}$-catenin-TCF-4 transcriptional activity was suppressed by phosphorylated STAT3; furthermore, STAT3 inactivation abolished this effect and elevated activated ${\beta}$-catenin levels. STAT3 also showed a strong interaction with SIAH-1, a regulator of active ${\beta}$-catenin via degradation, which stabilized SIAH-1 and increased its interaction with ${\beta}$-catenin. These results suggest that activated STAT3 regulates active ${\beta}$-catenin protein levels via stabilization of SIAH-1 and the subsequent ubiquitin-dependent proteasomal degradation of ${\beta}$-catenin in HEK293T cells.

• Korean Journal of Plant Resources
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• v.28 no.6
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• pp.727-733
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• 2015

Although Sophorae Flos (SF) has been reported to exert an anti-cancer activity, molecular targets and mechanisms associated with anti-cancer activity of SF have been unclear. Because cyclin D1 has been regarded as an important regulator in the cell proliferation, we focused cyclin D1 and investigated the effect of SF on the cyclin D1 regulation in light of elucidating the molecular mechanism for SF’s anti-cancer activity. The treatment of SF decreased cellular accumulation of cyclin D1 protein. However, SF did not change the level of cyclin D1 mRNA. Inhibition of proteasomal degradation by MG132 attenuated SF-mediated cyclin D1 downregulation and the half-life of cyclin D1 was decreased in the cells treated with SF. In addition, a point mutation of threonine-286 to alanine attenuated SF-mediated cyclin D1 downregulation. Inhibition of ERK1/2 by a selective inhibitor, PD98059 suppressed cyclin D1 downregulation by SF. From these results, we suggest that SF-mediated cyclin D1 downregulation may result from proteasomal degradation through its threonine-286 phosphorylation via ERK1/2. SF-induced proteasomal degradation of cyclin D1 might inhibit proliferation in human colorectal cancer cells. The current study provides information on molecular events for an anti-cancer activity of SF

• Korean Journal of Plant Resources
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• v.30 no.3
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• pp.265-271
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• 2017

In this study, we elucidated the molecular mechanism of silymarin by which silymarin may inhibits cell proliferation in human colorectal cancer cells in order to search the new potential anti-cancer target associated with the cell growth arrest. Silymarin reduced the level of c-Myc protein but not mRNA level indicating that silymarin-mediated downregulation of c-Myc may result from the proteasomal degradation. In the confirmation of silymarin-mediated c-Myc degradation, MG132 as a proteasome inhibitor attenuated c-Myc degradation by silymarin. In addition, silymarin phosphorylated the threonine-58 (Thr58) of c-Myc and the point mutation of Thr58 to alanine blocked its degradation by silymarin, which indicates that Thr58 phosphorylation may be an important modification for silymarin-mediated c-Myc degradation. We observed that the inhibition of ERK1/2, p38 and $GSK3{\beta}$ blocked the Thr58 phosphorylation and subsequent c-Myc degradation by silymarin. Finally, the point mutation of Thr58 to alanine attenuated silymarin-mediated inhibition of the cell growth. The results suggest that silymarin induces the cell growth arrest through c-Myc proteasomal degradation via ERK1/2, p38 and $GSK3{\beta}-dependent$ Thr58 phosphorylation.

• Korean Journal of Plant Resources
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• v.31 no.3
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• pp.218-227
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• 2018

In this study, we investigated the effect of the extracts from Vaccinium oldhamii on cell proliferation and the regulatory mechanisms of cyclin D1 protein level in human cancer cells. The branch extracts from Vaccinium oldhamii (VOB) showed higher inhibitor effect against the cell growth than leave extracts (VOL) and fruit extracts (VOF) in human colorectal cancer, breast cancer, prostate cancer, non-small lung cancer, pancreatic cancer and liver cancer cells. In addition, VOB decreased cyclin D1 level at both protein and mRNA level. MG132 treatment attenuated VOB-mediated cyclin D1 downregulation. A point mutation of threonine-286 to alanine attenuated cyclin D1 degradation by VOB. In addition, the inhibition of nuclear export by leptomycin B (LMB) attenuated cyclin D1 degradation by VOB. But, the treatment of PD98059 (ERK1/2 inhibitor), SB203580 (p38 inhibitor), SP600125 (JNK inhibitor), LiCl ($GSK3{\beta}$ inhibitor), LY294002 (PI3K inhibitor) or BAY 11-7082 ($I{\kappa}K$ inhibitor) did not affect VOB-induced cyclin D1 degradation. In conclusion, VOB induced cyclin D1 degradation through redistribution of cyclin D1 from the nucleus to cytoplasm via T286 phosphorylation of cyclin D1, which resulted in the inhibition of cancer cell proliferation.

• Korean Journal of Plant Resources
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• v.29 no.3
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• pp.297-304
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• 2016

The seed of safflower (Carthamus tinctorius L) has been reported to suppress human cancer cell proliferation. However, the mechanisms by which safflower seed inhibits cancer cell proliferation have remained nuclear. In this study, the inhibitory effect of the safflower seed (SS) on the proliferation of human colorectal cancer cells and the potential mechanism of action were examined. SS inhibited markedly the proliferation of human colorectal cancer cells (HCT116, SW480, LoVo and HT-29). In addition, SS suppressed the proliferation of human breast cancer cells (MDA-MB-231 and MCF-7). SS treatment decreased cyclin D1 protein level in human colorectal cancer cells and breast cancer cells. But, SS-mediated downregulated mRNA level of cyclin D1 was not observed. Inhibition of proteasomal degradation by MG132 attenuated cyclin D1 downregulation by SS and the half-life of cyclin D1 was decreased in SS-treated cells. In addition, SS increased cyclin D1 phosphorylation at threonine-286 and a point mutation of threonine-286 to alanine attenuated SS-mediated cyclin D1 degradation. Inhibition of ERK1/2 by PD98059 suppressed cyclin D1 phosphorylation and downregulation of cyclin D1 by SS. In conclusion, SS has anti-proliferative activity by inducing cyclin D1 proteasomal degradation through ERK1/2-dependent threonine-286 phosphorylation of cyclin D1. These findings suggest that possibly its extract could be used for treating colorectal cancer.

• Journal of Microbiology and Biotechnology
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• v.25 no.10
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• pp.1640-1647
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• 2015

We recently reported that the antimicrobial peptide Lumbricusin (NH₂-RNRRWCIDQQA), isolated from the earthworm, increases cell proliferation in neuroblastoma SH-SY5Y cells. Here, we investigated whether Lumbricusin has neurotropic activity in mouse neural stem cells (MNSCs) and a protective effect in a mouse model of Parkinson's disease (PD). In MNSCs isolated from mouse brains, Lumbricusin treatment significantly increased cell proliferation (up to 12%) and reduced the protein expression of p27^Kip1 through proteasomal protein degradation but not transcriptional regulation. Lumbricusin inhibited the 6-OHDA-induced apoptosis of MNSCs, and also showed neuroprotective effects in a mouse PD model, ameliorating the motor impairments seen in the pole, elevated body swing, and rotation tests. These results suggest that the Lumbricusin-induced promotion of neural cell proliferation via p27^Kip1 degradation has a protective effect in an experimental PD model. Thus, the antimicrobial peptide Lumbricusin could possibly be developed as a potential therapeutic agent for the treatment of PD.

• Korean Journal of Plant Resources
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• v.33 no.4
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• pp.271-278
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• 2020

In this study, we evaluated the anti-cancer activity and potential molecular mechanism of 70% ethanol extracts of the Berchemia floribunda (BF) which belongs to Rhamnaceae against human colorectal cancer cells. The treatment of BF decreased the cell proliferation in HCT116 cell and suppressed cellular accumulation of Cyclin D1 protein. Inhibition of proteasomal activity by MG132 attenuated BF-mediated Cyclin D1 downregulation and Cyclin D1 was decreased in the cell treated with BF. These findings indicates that BF-mediated Cyclin D1 downregulation may be result from Cyclin D1 proteasomal degradation. Additionally, BF-mediated Cyclin D1 degradation was blocked in the presence of LiCl, a GSK3β inhibitor, but not PD98059, SP600125, SB203580, Bay11-7082, LY294002 an ERK1/2 inhibitor, JNK inhibitor, p38 inhibitor, IκK inhibitor and PI3K inhibitor. Furthermore, BF phosphorylated Cyclin D1 at threonine-286 (Thr286), and LiCl-induced GSK3β inhibition reduced the BF mediated phosphorylation of Cyclin D1 at Thr286. These results suggested that BF may downregulate Cyclin D1 expression as a potential anti-cancer target through GSK3β dependent Cyclin D1 degradation. Therefore, this study provides that the extract of BF has anticancer activity against human colorectal cancer cells.

• Molecules and Cells
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• v.44 no.7
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• pp.444-457
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• 2021

Although the mechanism of chronic myeloid leukemia (CML) initiation through BCR/ABL oncogene has been well characterized, CML cell differentiation into erythroid lineage cells remains poorly understood. Using CRISPR-Cas9 screening, we identify Chromobox 8 (CBX8) as a negative regulator of K562 cell differentiation into erythrocytes. CBX8 is degraded via proteasomal pathway during K562 cell differentiation, which activates the expression of erythroid differentiation-related genes that are repressed by CBX8 in the complex of PRC1. During the differentiation process, the serine/threonine-protein kinase PIM1 phosphorylates serine 196 on CBX8, which contributes to CBX8 reduction. When CD235A expression levels are analyzed, the result reveals that the knockdown of PIM1 inhibits K562 cell differentiation. We also identify TRIM28 as another interaction partner of CBX8 by proteomic analysis. Intriguingly, TRIM28 maintains protein stability of CBX8 and TRIM28 loss significantly induces proteasomal degradation of CBX8, resulting in an acceleration of erythroid differentiation. Here, we demonstrate the involvement of the CBX8-TRIM28 axis during CML cell differentiation, suggesting that CBX8 and TRIM28 are promising novel targets for CML research.