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4β-Hydroxywithanolide E Modulates Alternative Splicing of Apoptotic Genes in Human Hepatocellular Carcinoma Huh-7 Cells

ABSTRACT: Alternative splicing is a mechanism for increasing the protein variety of a limited number of genes. Studies have shown that aberrant regulations of the alternative splicing of apoptotic gene transcripts may contribute to the development of cancer. In this study, we isolated 4β-Hydroxywithanolide E (4bHWE) from the traditional herb Physalis peruviana, and analyzed its biological effects in cancer cells. The results demonstrated that 4bHWE modulates the alternative splicing of apoptotic genes (e.g., HIPK3, SMAC/DIABLO, and SURVIVIN), changes the expression level of splicing factors (e.g., hnRNP C1/C2, ASF/SF2, SRp20, and SRp55), and induces histone tail posttranslational modifications (e.g., H3K27me1, H3K27me2, H3K36me3, and H3K79me1). Pretreatment with okadaic acid to inhibit protein phosphatase-1 could partly relieve the effects of 4bHWE on the alternative splicing of HIPK3 and SMAC/DIABLO transcripts, as well as on the dephosphorylation of ASF/SF2. Genome-wide detection of alternative splicing further indicated that several other apoptosis-related genes are also regulated by 4bHWE, including APAF1, CARP-1, and RIPK1. Moreover, we extended our study to apoptosis-associated molecules, detecting an increasing level of CASPASE-3 activity and cleavage of poly ADP-ribose polymerase in 4bHWE-induced apoptosis. Furthermore, in vivo experiments showed that the treatment of tumor-bearing mice with 4bHWE resulted in a marked decrease of tumor size and weight. Taken together, this study is the first to show that 4bHWE affects alternative splicing through the modulations of splicing factors, providing a novel view of the antitumor mechanism of 4bHWE.

ORGANISM(S): Homo sapiens

PROVIDER: GSE79884 | GEO | 2017/08/18

SECONDARY ACCESSION(S): PRJNA317320

REPOSITORIES: GEO

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Project description:Alternative splicing (AS) is a process that enables a mRNA to generate different protein isoforms that may have different biological functions or properties. Cancer cells often use this maneuverability to produce proteins that contribute to growth and survival. In previous study, we found that the antihypertensive drug amiloride has a novel biological function that regulates the AS on human cancer cells. However, it also showed that the effective concentration of amiloride in cancer treatment is too high to limit its use in future therapeutic application. In this study, we therefore used computational algorithms to predict the potential amiloride derivatives and found that BS008 is the most promising compound in all derivatives. The results demonstrated that BS008 can modulate the AS of apoptotic gene transcripts, including HIPK3, SMAC, and BCLX in cancer cells. Splicing regulatory involved a variety of histone modifications and splicing factors, and accompanied the changed of phosphorylation state of SR proteins during the splicing process. Inhibition of protein phosphatase-1 with okadaic acid pretreatment partially alleviated the effects of BS008 on the AS of HIPK3 and SMAC transcripts, as well as on the phosphorylation levels of SRSF3. RNA sequencing further discovered that the AS of many other apoptosis-related gene transcripts such as AATF, ATM, AIFM1, NFKB1, and API5 was modulated by BS008. We extended the study to apoptosis-associated molecules, and detected decreased levels of BCLX and increased levels of BAX and active CASPASE-3 in BS008-induced apoptosis. In vivo experiments indicated that the treatment of tumor-bearing mice with BS008 resulted in a marked decrease in tumor size. The combination BS008/sorafenib enhances anti-tumor activity of sorafenib and allows dose reduction of sorafenib without compromising its anti-tumor activity. In conclusion, these findings suggested that BS008, an amiloride derivative, may provide therapeutic potential for cancer treatment in future.

Project description:Screening small molecules and drugs for activity to modulate alternative splicing, we found that amiloride, distinct from four other intracellular pH-affecting analogues, could “normalize” the splicing of BCL-X, HIPK3 and RON/MISTR1 transcripts in human hepatocellular carcinoma Huh-7 cells. To elucidate the underlying mechanisms, our proteomic analyses of amiloride-treated cells detected hypo-phosphorylation of splicing factor SF2/ASF and also decreased levels of SRp20 and two un-identified SR proteins. We further observed decreased phosphorylation of AKT, ERK1/2 and PP1, while increased phosphorylation of p38 and JNK, suggesting that amiloride treatment down-regulated kinases and up-regulated phosphatases in the signal pathways known to affect the splicing factor protein phosphorylation. The amiloride effects of splicing factor protein hypo-phosphorylation and“normalized”oncogenic RNA splicing were both abrogated by pre-treatment with a PP1 inhibitor. We then performed global exon array analysis of Huh-7 cells treated with amiloride for 24 hours. Using gene array chips (Affymetrix GeneChip® Human Exon 1.0 ST Array of >518000 exons of 42974 genes) for exon array analysis (set parameters of correlation coefficient ≥ 0.7, splicing index ≤ -1.585 , and log2 ratio ≤ -1.585), we found that amiloride influenced the splicing patterns of 551 genes involving at least 584 exons, which included 495 known protein-coding genes involving 526 exons, many of which play key roles in functional networks of ion transport, extracellular matrix, cytoskeletons and genome maintenance. Cellular functional analyses revealed subsequent invasion and migration defects, cell cycle disruption, cytokinesis impairment, and lethal DNA degradation in amiloride-treated Huh-7 cells. This study thus provides mechanistic underpinnings for exploiting small molecule modulation of abnormal RNA splicing for cancer therapeutics. Target was prepared from 3 biological replicates of 0.5mM amiloride-treatment for 24hr and 3 control untreatment from Huh7 cell line and hybridized to the Affymetrix Human Exon 1.0 ST Array. The values of the hybridized probesets were normalized and analyzed for gene expression using dChip2010 software.

Project description:Metastatic malignant melanoma is the deadliest skin cancer type, and it is characterized by its high resistance to apoptosis. The main driving mutations in melanoma cause hyperactivation of genes within the ERK pathway, with BRAF mutations being the most frequent ones, followed by NRAS, NF1 and MEK mutations. Increasing evidence shows that the MST2/Hippo pathway is also deregulated in this cancer type. While mutations are rare, MST2/Hippo pathway core proteins expression levels are often dysregulated in melanoma. The expression of the tumour suppressor RASSF1A, a bona fide activator of the pro-apoptotic MST2 pathway, is silenced by promoter methylation in over half of melanomas and correlates with poor prognosis. Here, using mass spectrometry-based interaction proteomics we identified Second Mitochondria-derived Activator of Caspases (SMAC) as a novel LATS1 interactor. We show that RASSF1A-dependent activation of the pro-apoptotic MST2 pathway promotes LATS1-SMAC interaction and negatively regulates the anti-apoptotic signal mediated by the members of the IAP family. Moreover, proteomic experiments identified a common cluster of the apoptotic regulator that bind to SMAC and LATS1. Mechanistic analysis show that the LATS1-SMAC complex promotes XIAP ubiquitination and its subsequent degradation which ultimately results apoptosis. Importantly, we show that the oncogenic BRAFV600E mutant prevents the pro-apoptotic signal mediated by the LAST1-SMAC complex while treatment of melanoma cell lines with BRAF inhibitors promotes this complex, indicating that inhibition of the LATS1-SMAC might be necessary for BRAFV600E-driven melanoma. Finally, we show that LATS1-SMAC interaction is regulated by the SMAC mimetic Birinapant which requires the inhibition of C-IAP1 and the degradation of XIAP, indicating that the MST2/Hippo pathway is part of the mechanism of action of Birinapant. Overall, the current work shows SMAC-dependent apoptosis is regulated by the LATS1 tumour suppressor and supports the idea that LATS1 is a signalling hub that regulates the crosstalk between the MST2 pathway, the apoptotic network and the RAF/ERK pathway.

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4β-Hydroxywithanolide E Modulates Alternative Splicing of Apoptotic Genes in Human Hepatocellular Carcinoma Huh-7 Cells

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