Guiying Shi

SENP3 is responsible for HIF-1 transactivation under mild oxidative stress via p300 de-SUMOylation

The physiological function of Sentrin/SUMO‐specific proteases (SENPs) remains largely unexplored, and little is known about the regulation of SENPs themselves. Here, we show that a modest increase of reactive oxygen species (ROS) regulates SENP3 stability and localization. We found that SENP3 is continuously degraded through the ubiquitin‐proteasome pathway under basal condition and that ROS inhibit this degradation. Furthermore, ROS causes SENP3 to redistribute from the nucleoli to the nucleoplasm, allowing it to regulate nuclear events. The stabilization and redistribution of SENP3 correlate with an increase in the transcriptional activity of the hypoxia‐inducing factor‐1 (HIF‐1) under mild oxidative stress. ROS‐enhanced HIF‐1 transactivation is blocked by SENP3 knockdown. The de‐SUMOylating activity of SENP3 is required for ROS‐induced increase of HIF‐1 transactivation, but the true substrate of SENP3 is the co‐activator of HIF‐1α, p300, rather than HIF‐1α itself. Removing SUMO2/3 from p300 enhances its binding to HIF‐1α. In vivo nude mouse xenografts overexpressing SENP3 are more angiogenic. Taken together, our results identify SENP3 as a redox sensor that regulates HIF‐1 transcriptional activity under oxidative stress through the de‐SUMOylation of p300.

Redox regulation of the stability of the SUMO protease SENP3 via interactions with CHIP and Hsp90

The molecular chaperone heat shock protein 90 (Hsp90) and the co‐chaperone/ubiquitin ligase carboxyl terminus of Hsc70‐interacting protein (CHIP) control the turnover of client proteins. How this system decides to stabilize or degrade the client proteins under particular physiological or pathological conditions is unclear. We report here a novel client protein, the SUMO2/3 protease SENP3, that is sophisticatedly regulated by CHIP and Hsp90. SENP3 is maintained at a low basal level under non‐stress condition due to Hsp90‐independent CHIP‐mediated ubiquitination. Upon mild oxidative stress, SENP3 undergoes thiol modification, which recruits Hsp90. Hsp90/SENP3 association protects SENP3 from CHIP‐mediated ubiquitination and subsequent degradation, but this effect of Hsp90 requires the presence of CHIP. Our data demonstrate for the first time that CHIP and Hsp90 interplay with a client alternately under non‐stress and stress conditions, and the choice between stabilization and degradation is made by the redox state of the client. In addition, enhanced SENP3/Hsp90 association is found in cancer. These findings provide new mechanistic insight into how cells regulate the SUMO protease in response to oxidative stress.

Emodin enhances cytotoxicity of chemotherapeutic drugs in prostate cancer cells: The mechanisms involve ROS-mediated suppression of multidrug resistance and hypoxia inducible factor-1

The intrinsic or acquired resistance to multiple drugs (MDR) of cancer cells remains one of the main obstacles for chemotherapy. Development of small molecule targeting to hypoxia inducible factor-1 (HIF-1) has been recently proposed as strategy for treatments of drug-resistant solid tumors. In the present study, emodin, proven as a reactive oxygen species (ROS) generator by our previous work, was applied in combination with cisplatin and other chemotherapeutic drugs in the multidrug resistant prostate carcinoma cell line DU-145 and normal human dermal fibroblasts. Results showed that emodin/cisplatin co-treatment remarkably elevated ROS level and enhanced chemosensitivity in DU-145 cells, compared with cisplatin-only treatment, but exerted little effect on non-tumor cells. The effect of co-treatment on MDR1 gene and its upstream regulator HIF-1 was then investigated in DU-145. Co-treatment down-regulated MDR1 expression and promoted drug retention, and meanwhile suppressed transactivation of HIF-1 in response to hypoxia without changing expression of HIF-1α. The experiments on tumor-bearing mice showed that co-treatment inhibited the tumor growth in vivo, owing to oxidative stress and MDR1 down-regulation within tumors. HIF-1 transactivation and clonegenisis were suppressed in cells isolated from the tumors. Finally, examinations for the body weight, the organ histology and the antioxidant capacity of serum suggested that no systemic toxicity related to co-treatment was discernable. In conclusions, emodin, as a novel small inhibitor of HIF-1, may be recognized an effective adjunctive to improve efficacy of cytotoxic drugs in prostate cancer cells with over-activated HIF-1 and potent MDR.

SENP3-mediated De-conjugation of SUMO2/3 from Promyelocytic Leukemia Is Correlated with Accelerated Cell Proliferation under Mild Oxidative Stress

Small ubiquitin-like modifier (SUMO) 2/3 is known to conjugate to substrates in response to a variety of cellular stresses. However, whether and how SUMO2/3-specific proteases are involved in de-conjugation under cell stress is unclear. Here, we show that low doses of hydrogen peroxide (H2O2) induce an increase of the SENP3 protein, which removes SUMO2/3 from promyelocytic leukemia (PML). Low dose H2O2 causes SENP3 to co-localize with PML bodies and reduces the number of PML bodies in a SENP3-dependent manner. Furthermore, de-conjugation of SUMO2/3 from PML is responsible for the accelerated cell proliferation caused by low dose H2O2. Knocking down PML promotes basal cell proliferation as expected. This can be reversed by reconstitution with wild-type PML but not its mutant lacking SUMOylation, indicating that only the SUMOylated PML can play an inhibitory role for cell proliferation. Thus, SENP3 appears to be a key mediator in mild oxidative stress-induced cell proliferation via regulation of the SUMOylation status of PML. Furthermore, SENP3 is over-accumulated in a variety of primary human cancers including colon adenocarcinoma in which PML is hypo-SUMOylated. These results reveal an important role of SENP3 and the SUMOylation status of PML in the regulation of cell proliferation under oxidative stress.

Emodin enhances sensitivity of gallbladder cancer cells to platinum drugs via glutathion depletion and MRP1 downregulation

Glutathione conjugation and transportation of glutathione conjugates of anticancer drugs out of cells are important for detoxification of many anticancer drugs. Inhibition of this detoxification system has recently been proposed as a strategy to treat drug-resistant solid tumors. Gallbladder carcinoma is resistant to many anticancer drugs, therefore, it is needed to develop a novel strategy for cancer therapy. In the present study, we tested the effect of emodin (1,3,8-trihydroxy-6-methylanthraquinone), a reactive oxygen species (ROS) generator reported by our group previously, in combination with cisplatin (CDDP), carboplatin (CBP) or oxaliplatin in treating the gallbladder carcinoma cell line SGC996. Our results showed that co-treatment with emodin could remarkably enhance chemosensitivity of SGC996 cells in comparison with cisplatin, carboplatin or oxaliplatin treatment alone. We found that the mechanisms may be attributed to reduction of glutathione level, and downregulation of multidrug resistance-related protein 1 (MRP1) expression in SGC996 cells. The experiments on tumor-bearing mice showed that emodin/cisplatin co-treatment inhibited the tumor growth in vivo via increasing tumor cell apoptosis and downregulating MRP1 expression. In conclusion, emodin can work as an adjunct to enhance the anticancer effect of platinum drugs in gallbladder cancer cells via ROS-related mechanisms.

Emodin as an effective agent in targeting cancer stem-like side population cells of gallbladder carcinoma.

Side population (SP) cells are previously identified from bone marrow based on their capacity to efflux of the fluorescent dye Hoechst 33342. Recent studies demonstrate that SP cells isolated from various cancer cell lines and primary tumors possess stem-cell-like properties. Thus, targeting tumor SP cells may provide new strategies for treatment in clinic. We previously showed that 1,3,8-trihydroxy-6-methylanthraquinone (emodin), a reactive oxygen species (ROS) generator, enhanced sensitivity of gallbladder cancer SGC-996 cells to cisplatin (CDDP) via generation of ROS and downregulation of multidrug-resistance-associated protein 1 (MRP1). To determine whether emodin also acts effectively on cancer stem cells of gallbladder carcinoma, we use SP cells as a model of cancer stem-cell-like cells. Here, we found that emodin, via ROS-related mechanism and suppressing the function of ATP-binding cassette super-family G member (ABCG2), which is known to be associated with Hoechst dye efflux activity of SP cells, not only reduced the ratio, inhibited clone formation, and eliminated sphere formation of SP cells effectively, but also promoted obviously the intracellular accumulation of doxorubicin, the main substrate of the efflux pump ABCG2. In addition, emodin could sensitize CDDP, via inhibition of expression of ABCG2, to overcome chemoresistance of SP cells. Importantly, similar to the experiment in vitro, emodin/CDDP co-treatment in vivo suppressed the tumor growth derived from SP cells through downregulating ABCG2 expression. Our results suggest that emodin is an effective agent targeting cancer stem-like SP cells of gallbladder carcinoma, either alone or acts as a chemotherapy enhancer.

SUMO2 and SUMO3 transcription is differentially regulated by oxidative stress in an Sp1-dependent manner

Protein SUMOylation (SUMO is small ubiquitin-related modifier) is a dynamic process that is strictly regulated under physiological and pathological conditions. However, little is known about how various intra- or extra-cellular stimuli regulate expression levels of components in the SUMO system. SUMO isoforms SUMO2 and SUMO3 can rapidly convert to be conjugated in response to a variety of cellular stresses. Owing to the limitations of sequence homology, SUMO2 and SUMO3 cannot be differentiated between and are thus referred to as SUMO2/3. Whether these two isoforms are regulated in distinct manners has never been addressed. In the present paper we report that the expression of SUMO3, but not SUMO2, can be down-regulated at the transcription level by cellular oxidative stress. In the present study, we checked SUMO2 and SUMO3 mRNA levels in cells exposed to various doses of H2O2 and in cells bearing different levels of ROS (reactive oxygen species). We found an inverse relationship between SUMO3 transcription and ROS levels. We characterized a promoter region specific for the mouse Sumo3 gene that is bound by the redox-sensitive transcription factor Sp1 (specificity protein 1) and demonstrated oxidation of Sp1, as well as suppression of Sp1-DNA binding upon oxidative stress. This revealed for the first time that the expression of SUMO2 and SUMO3 is regulated differently by ROS. These findings may enhance our understanding about the regulation of SUMOylation and also shed light on the functions of Sp1.

PML/RARα fusion protein mediates the unique sensitivity to arsenic cytotoxicity in acute promyelocytic leukemia cells: Mechanisms involve the impairment of cAMP signaling and the aberrant regulation of NADPH oxidase†

Acute promyelocytic leukemia (APL) cells are characterized by PML/RARα fusion protein, high responsiveness to arsenic trioxide (ATO)‐induced cytotoxicity and an abundant generation of reactive oxygen species (ROS). In this study we investigated the association among these three features in APL‐derived NB4 cells. We found that NADPH oxidase‐derived ROS generation was more abundant in NB4 cells compared with monocytic leukemia U937 cells. By using PR9, a sub‐line of U937 stably transduced with the inducible PML/RARα expression vectors, we attributed disparities on ROS generation and ATO sensitivity to the occurrence of PML/RARα fusion protein, since PML/RARα‐expressing cells appeared higher NADPH oxidase activity, higher ROS level and higher sensitivity to ATO. On the other hand, the basal intensity of cAMP signaling pathway was compared between NB4 and U937 as well as between PR9 cells with or without PML/RARα, demonstrating that PML/RARα‐expressing cells had an impaired cAMP signaling pathway which relieved its inhibitory effect on NADPH oxidase derived ROS generation. In summary, the present study demonstrated the correlation of PML/RARα with cAMP signaling pathway, NADPH oxidase and ROS generation in APL cells. PML/RARα that bestows NB4 cells various pathological features, paradoxically also endows these cells with the basis for susceptibility to ATO‐induced cytotoxcity. J. Cell. Physiol. 217: 486–493, 2008.

Emodin enhances cisplatin-induced cytotoxicity in human bladder cancer cells through ROS elevation and MRP1 downregulation.

BackgroundChemoresistance is one of the most leading causes for tumor progression and recurrence of bladder cancer. Reactive oxygen species (ROS) plays a key role in the chemosensitivity of cancer cells. In the present study, emodin (1,3,8-trihydroxy-6-methylanthraquinone) was applied as a ROS generator in combination with cisplatin in T24 and J82 human bladder cancer cells.MethodsCell viability and apoptosis rate of different treatment groups were detected by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) and flow cytometry (FCM). The expression of transporters was measured at both the transcription and translation levels using PCR and western blotting. In vitro findings were confirmed by in vivo experiments using tumor-bearing mice. The expression of multidrug resistance-associated protein 1 (MRP1) in tumour tissue was measured using immunohistochemistry and side effects of the emodin/cisplatin co-treatment were investigated by histological examination.ResultsEmodin increased the cellular ROS level and effectively enhanced the cisplatin-induced cytotoxicity of T24 and J82 human bladder cancer cells through decreasing glutathione-cisplatin (GSH-cisplatin) conjugates. It blocked the chemoresistance of T24 and J82 cells to cisplatin through suppressing the expression of MRP1. This effect was specific in T24 and J82 cells but not in HCV-29 normal bladder epithelial cells. Consistent with in vitro experiments, emodin/cisplatin co-treatment increased the cell apoptosis and repressed the MRP1 expression in xenograft tumors, and without obvious systemic toxicity.ConclusionsThis study revealed that emodin could increase the cisplatin-induced cytotoxicity against T24 and J82 cells via elevating the cellular ROS level and downregulating MRP1 expression. We suggest that emodin could serve as an effective adjuvant agent for the cisplatin-based chemotherapy of bladder cancer.