The NAD-dependent deacetylase sirtuin 1 (SIRT1), a member of the mammalian sirtuin family, plays a pivotal role in deacetylating histone and nonhistone proteins. Recently, it has been reported that ...SIRT1 is upregulated in various kinds of tumors and is associated with cell growth and metastasis. However, the factors and molecular mechanism regulating its cellular levels remain to be clarified. Here, we reported that the E3 ubiquitin ligase SMURF2 interacts with SIRT1 and mediates its ubiquitination and degradation. Depletion of SMURF2 leads to SIRT1 upregulation and induces the tumor formation and growth of colorectal cancer in vitro and in vivo. Furthermore, we show a negative correlation between SIRT1 and SMURF2 expression in human colorectal cancer. Thus, we propose a novel mechanism of colorectal tumorigenesis via SIRT1 regulation by SMURF2, which could potentially give rise to a new strategy for the treatment of colorectal cancer.
Aberrant expression of splicing factors was found to promote tumorigenesis and the development of human malignant tumors. Nevertheless, the underlying mechanisms and functional relevance remain ...elusive. We here show that USP39, a component of the spliceosome, is frequently overexpressed in high-grade serous ovarian carcinoma (HGSOC) and that an elevated level of USP39 is associated with a poor prognosis. USP39 promotes proliferation/invasion in vitro and tumor growth in vivo. Importantly, USP39 was transcriptionally activated by the oncogene protein c-MYC in ovarian cancer cells. We further demonstrated that USP39 colocalizes with spliceosome components in nuclear speckles. Transcriptomic analysis revealed that USP39 deletion led to globally impaired splicing that is characterized by skipped exons and overrepresentation of introns and intergenic regions. Furthermore, RNA immunoprecipitation sequencing showed that USP39 preferentially binds to exon-intron regions near 5' and 3' splicing sites. In particular, USP39 facilitates efficient splicing of HMGA2 and thereby increases the malignancy of ovarian cancer cells. Taken together, our results indicate that USP39 functions as an oncogenic splicing factor in ovarian cancer and represents a potential target for ovarian cancer therapy.
Isoliensinine, liensinine and neferine are major bisbenzylisoquinoline alkaloids in the seed embryo of lotus (Nelumbo nucifera), and exhibit potential anti-cancer activity. Here, we explored the ...effects of these alkaloids on triple-negative breast cancer cells and found that among the three alkaloids isoliensinine possesses the most potent cytotoxic effect, primarily by inducing apoptosis. Interestingly, isoliensinine showed a much lower cytotoxicity against MCF-10A, a normal human breast epithelial cell line. Further studies showed that isoliensinine could significantly increase the production of reactive oxygen species (ROS) in triple-negative breast cancer cells, but not in MCF-10A cells. The isoliensinine-induced apoptosis could be attenuated by radical oxygen scavenger N-acetyl cysteine, suggesting that the cytotoxic effect of isoliensinine on cancer cells is at least partially achieved by inducing oxidative stress. We found that both p38 MAPK and JNK signaling pathways were activated by isoliensinine treatment and contributed to the induction of apoptosis. Furthermore, inhibitors or specific siRNAs of p38 MAPK and JNK could attenuate apoptosis induced by isoliensinine. However, only the p38 inhibitor or p38-specific siRNA blocked the elevation of ROS in isoliensinine-treated cells. Our findings thus revealed a novel antitumor effect of isoliensinine on breast cancer cells and may have therapeutic implications.
Upregulation of special AT-rich sequence-binding protein-1 (SATB1) has been suggested to promote tumor growth and metastasis. However, the factors governing its cellular levels remain unclear. Here, ...we report that ubiquitin-specific peptidase 47 (USP47), a member of the deubiquitinating enzymes family, interacts with SATB1 and mediates its deubiquitination and stability. USP47 deficiency impairs transcriptional activity of SATB1 target genes and inhibits colon cancer cell proliferation, migration, and tumorigenesis in a mouse model of colon cancer. Furthermore, we identified SMURF2 as an E3 ubiquitin ligase that promotes SATB1 degradation by upregulating its ubiquitination, and its deficiency promotes colon cancer cell proliferation and SATB1 target gene transcription. SMURF2 is negatively regulated by USP47, and USP47 depletion sensitizes colon cancer cells to 5-FU treatment-induced apoptosis. Taken together, our findings provide a ubiquitination-related mechanistic link to USP47, SMURF2, and SATB1 and suggest that USP47 might be targeted for colon cancer treatment when SATB1 is overexpressed.
•SATB1, a tumor-promoting factor in colorectal cancer (CRC), was identified as a substrate of deubiquitinase USP47.•USP47 promotes colon cancer cell growth and migration through SATB1.•USP47 reprograms the expression profiles of cell growth and tumor metastasis-related genes.•SMURF2 is an E3 ubiquitin ligase of SATB1 that promotes its proteasome-mediated degradation.•USP47/SATB1 depletion sensitizes colon cancer cells to apoptosis.
Glioblastoma multiforme (GBM) is the most common primary malignant brain tumor and has a poor prognosis. We, here, report a potent antitumor effect of berberine, an isoquinoline alkaloid, on GBM. ...Berberine was found to have an IC50 that is much lower than temozolomide in vitro in U87, U251, and U118 glioblastoma cells. Although previous studies showed that berberine primarily exerts its anticancer effect by inducing cell-cycle arrest, apoptosis, and autophagy, we observed that the antitumor effect of berberine on glioblastoma cells was primarily achieved through induction of cellular senescence. In glioblastoma cells treated with berberine, the level of epidermal growth factor receptor (EGFR) was greatly reduced. Examination of the activities of the kinases downstream of EGFR revealed that the RAF-MEK-ERK signaling pathway was remarkably inhibited, whereas AKT phosphorylation was not altered. Pharmacologic inhibition or RNA interference of EGFR similarly induced cellular senescence of glioblastoma cells. Furthermore, the cellular senescence induced by berberine could be rescued by introduction of a constitutive active MKK. Berberine also potently inhibited the growth of tumor xenografts, which was accompanied by downregulation of EGFR and induction of senescence. Our findings thus revealed a new route by which berberine exerts its anticancer activity. Because EGFR is commonly upregulated in glioblastoma, the demonstration of effective inhibition of EGFR by berberine points to the possibility of using berberine in the treatment of patients with glioblastoma.
The reduced protein expression of SIRT6 tumor suppressor is involved in tumorigenesis. The molecular mechanisms underlying SIRT6 protein downregulation in human cancers remain unknown. Using a ...proteomic approach, we have identified the ubiquitin-specific peptidase USP10, another tumor suppressor, as one of the SIRT6-interacting proteins. USP10 suppresses SIRT6 ubiquitination to protect SIRT6 from proteasomal degradation. USP10 antagonizes the transcriptional activity of the c-Myc oncogene through SIRT6, as well as p53, to inhibit cell-cycle progression, cancer cell growth, and tumor formation. To support this conclusion, we detected significant reductions in both USP10 and SIRT6 protein expression in human colon cancers. Our study discovered crosstalk between two tumor-suppressive genes in regulating cell-cycle progression and proliferation and showed that dysregulated USP10 function promotes tumorigenesis through SIRT6 degradation.
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•USP10 is identified as a SIRT6 interactor in human colon cancer cells•USP10 deubiquitinates and stabilizes SIRT6•USP10 antagonizes c-Myc transcriptional activity through SIRT6 and p53•USP10 and SIRT6 protein expressions are reduced in human colon cancers
SIRT6 has recently emerged as a tumor suppressor, and its reduced protein expression has been detected in human cancers. Factors that downregulate SIRT6 in tumorigenesis remain to be identified. Fang and colleagues report that USP10, another tumor suppressor, is a SIRT6-specific deubiquitinase. USP10 stabilizes SIRT6 protein to inhibit the oncogenic c-Myc in cancer cells. Downregulation of USP10 is positively associated with Sirt6 reduction in human cancers. Therefore, crosstalk between these two tumor suppressors is critical in tumorigenesis.
High-grade serous ovarian carcinoma (HGSOC) accounts for the highest number of deaths among patients with epithelial ovarian cancer. However, the molecular mechanisms underlying HGSOC tumorigenesis ...are currently unclear. In the present study, a lentiviral expression system was employed to manipulate forkhead box D1 (FOXD1) expression in ovarian cancer cells. Immunohistochemical staining was used to examine the expression of FOXD1 in tissue samples. Clonogenic and MTT assays were employed to evaluate cell proliferation, and flow cytometry was applied for cell cycle analysis. Dual-luciferase reporter and chromatin immunopre-cipitation assays were used to determine the role of FOXD1 in regulating p21 expression. The results demonstrated that FOXD1 expression was downregulated in HGSOC, and high expression levels of FOXD1 were found to be a predictor of good prognosis. FOXD1 significantly inhibited the proliferation of human ovarian cancer cells and induced cell cycle arrest at G1 phase in vitro. In addition, exogenous FOXD1 expression inhibited ovarian cancer cell growth in vivo. Furthermore, microRNA (miR)-30a-5p and miR-200a-5p were observed to be upregulated in HGSOC, and function as direct negative regulators of FOXD1 by targeting its 3'-untranslated region. The present study also revealed that FOXD1 promotes p21 expression in a p53-independent manner. In conclusion, the results of the present study indicate a direct association between FOXD1 and p21 that may be mediated by miR-30a-5p and miR-200a-5p. The authors hypothesize that FOXD1 may serve as a biomarker or therapeutic target in HGSOC. Key words: high-grade serous ovarian carcinoma, forkhead box D1, proliferation, p21, microRNA-30a-5p, microRNA-200a-5p, prognosis
Dysregulated expression of splicing factors has important roles in cancer development and progression. However, it remains a challenge to identify the cancer-specific splicing variants. Here we ...demonstrate that spliceosome component BUD31 is increased in ovarian cancer, and its higher expression predicts worse prognosis. We characterize the BUD31-binding motif and find that BUD31 preferentially binds exon-intron regions near splicing sites. Further analysis reveals that BUD31 inhibition results in extensive exon skipping and a reduced production of long isoforms containing full coding sequence. In particular, we identify BCL2L12, an anti-apoptotic BCL2 family member, as one of the functional splicing targets of BUD31. BUD31 stimulates the inclusion of exon 3 to generate full-length BCL2L12 and promotes ovarian cancer progression. Knockdown of BUD31 or splice-switching antisense oligonucleotide treatment promotes exon 3 skipping and results in a truncated isoform of BCL2L12 that undergoes nonsense-mediated mRNA decay, and the cells subsequently undergo apoptosis. Our findings reveal BUD31-regulated exon inclusion as a critical factor for ovarian cancer cell survival and cancer progression.
PARP inhibitors have been widely tested in clinical trials, especially for the treatment of breast cancer and ovarian cancer, and were shown to be highly successful. Because PARP primarily functions ...in sensing and repairing DNA strand breaks, the therapeutic effect of PARP inhibition is generally believed to be attributed to impaired DNA repair. We here report that oxidative stress is also increased by PARP inhibition and mediates the antitumor effect. We showed that PARP1 is highly expressed in specimens of high grade serous ovarian carcinoma and its activity is required for unperturbed proliferation of ovarian cancer cells. Inhibition or depletion of PARP leads to not only an increase in DNA damage, but also an elevation in the levels of reactive oxygen species (ROS). Importantly, antioxidant N-acetylcysteine (NAC) significantly attenuated the induction of DNA damage and the perturbation of proliferation by PARP inhibition or depletion. We further showed that NADPH oxidases 1 and 4 were significantly upregulated by PARP inhibition and were partially responsible for the induction of oxidative stress. Depletion of NOX1 and NOX4 partially rescued the growth inhibition of PARP1-deficient tumor xenografts. Our findings suggest that in addition to compromising the repair of DNA damage, PARP inhibition or depletion may exert extra antitumor effect by elevating oxidative stress in ovarian cancer cells.
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•PARP1 is overexpressed in ovarian cancer.•PARP inhibition increases oxidative stress and oxidative DNA damage.•PARP inhibition increases ROS by upregulating NOX1 and NOX4.•Oxidative stress mediates the antitumor effect of PARP inhibition.
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