Hepatocyte Cell Cycle Progression Depends on a Transcriptional Repressor Cascade Downstream of Wnt Signaling

Cell proliferation is tightly controlled by inhibitors that block cell cycle progression until growth signals relieve this inhibition. In several tissues including the liver, transcriptional repressors such as E2F7 and E2F8 function as inhibitors of mitosis and promote polyploidy, but how growth factors release these mitotic inhibitors to facilitate cell cycle progression is unknown. We describe here a newly identified mechanism of cell division control in which Wnt/βcatenin signaling in the postnatal liver maintains active hepatocyte proliferation through Tbx3, a Wnt target gene. TBX3 directly represses transcription of E2f7 and E2f8, promoting a low ploidy state and cell cycle progression. This sequential transcriptional repressor cascade, initiated by Wnts, provides a new paradigm for exploring how a commonly active developmental signal impacts cell cycle completion.

lncRNA SNHG9 Promotes Cell Proliferation, Migration, and Invasion in Human Hepatocellular Carcinoma Cells by Increasing GSTP1 Methylation, as Revealed by CRISPR-dCas9

Hepatocellular carcinoma (HCC) is among the major causes of cancer-related mortalities globally. Long non-coding RNAs (LncRNAs), as epigenetic molecules, contribute to malignant tumor incidences and development, including HCC. Although LncRNA SNHG9 is considered an oncogene in many cancers, the biological function and molecular mechanism of SNHG9 in HCC are still unclear. We investigated the effects of lncRNA SNHG9 on the methylation of glutathione S-transferase P1 (GSTP1) and the progression of HCC. Histological data analysis, CRISPR-dCas9, and cytological function experiment were used to study the expression level and biological function of SNHG9 in HCC. There was an upregulated expression of SNHG9 in HCC, which was associated with shorter disease-free survival. Knockdown of SNHG9 can inhibit cell proliferation, block cell cycle progression, and inhibit cell migration and invasion by upregulating GSTP1. LncRNA SNHG9 recruits methylated enzymes (DNMT1, DNMT3A, and DNMT3B) to increase GSTP1 promoter methylation, a common event in the development of HCC. Inhibition of lncRNA SNHG9 demethylates GSTP1, which prevents HCC progression, presents a promising therapeutic approach for HCC patients.

The Anti-Cancer Effects of Anti-Parasite Drug Ivermectin in Ovarian Cancer

Ivermectin is an old, common, and classic anti-parasite drug, which has been found to have a broad-spectrum anti-cancer effect on multiple human cancers. This chapter will focus on the anti-cancer effects of ivermectin on ovarian cancer. First, ivermectin was found to suppress cell proliferation and growth, block cell cycle progression, and promote cell apoptosis in ovarian cancer. Second, drug pathway network, qRT-PCR, and immunoaffinity blot analyses found that ivermectin acts through molecular networks to target the key molecules in energy metabolism pathways, including PFKP in glycolysis, IDH2 and IDH3B in Kreb’s cycle, ND2, ND5, CYTB, and UQCRH in oxidative phosphorylation, and MCT1 and MCT4 in lactate shuttle, to inhibit ovarian cancer growth. Third, the integrative analysis of TCGA transcriptomics and mitochondrial proteomics in ovarian cancer revealed that 16 survival-related lncRNAs were mediated by ivermectin, SILAC quantitative proteomics analysis revealed that ivermectin extensively inhibited the expressions of RNA-binding protein EIF4A3 and 116 EIF4A3-interacted genes including those key molecules in energy metabolism pathways, and also those lncRNAs regulated EIF4A3-mRNA axes. Thus, ivermectin mediated lncRNA-EIF4A3-mRNA axes in ovarian cancer to exert its anticancer capability. Further, lasso regression identified the prognostic model of ivermectin-related three-lncRNA signature (ZNRF3-AS1, SOS1-IT1, and LINC00565), which is significantly associated with overall survival and clinicopathologic characteristics in ovarian cancer patients. These ivermectin-related molecular pattern alterations benefit for prognostic assessment and personalized drug therapy toward 3P medicine practice in ovarian cancer.

A New Method for Chromosomes Preparation by ATP-Competitive Inhibitor SP600125 via Enhancement of Endomitosis in Fish

Previous studies have suggested that 1,9-Pyrazoloanthrone, known as SP600125, can induce cell polyploidization. However, what is the phase of cell cycle arrest caused by SP600125 and the underlying regulation is still an interesting issue to be further addressed. Research in this article shows that SP600125 can block cell cycle progression at the prometaphase of mitosis and cause endomitosis. It is suggested that enhancement of the p53 signaling pathway and weakening of the spindle assembly checkpoint are associated with the SP600125-induced cell cycle arrest. Using preliminary SP600125 treatment, the samples of the cultured fish cells and the fish tissues display a great number of chromosome splitting phases. Summarily, SP600125 can provide a new protocol of chromosomes preparation for karyotype analysis owing to its interference with prometaphase of mitosis.

MicroRNAs Restrain Proliferation in BRAFV600E Melanocytic Nevi

Benign melanocytic nevi commonly form when melanocytes that acquire a BRAFV600E mutation undergo a period of rapid proliferation and subsequent arrest. Constitutive activation of MAPK signaling downstream of BRAF drives the initial proliferative phenotype. However, the factors that establish and maintain growth arrest in nevi remain elusive. The growth-arrested state of BRAFV600E melanocytes is not conferred by additional genetic mutations, suggesting a role for regulatory elements. We investigated the role of microRNAs in the initiation and maintenance of nevus arrest. Using primary human melanocytes, melanocytic nevi, and adjacent melanoma, we show that MIR211-5p and MIR328-3p are enriched in nevi compared to normal melanocytes, then subsequently downregulated in adjacent melanoma. Both MIR211-5p and MIR328-3p proved necessary effectors of BRAFV600E-induced growth arrest in human melanocytes. We identified microRNA target networks which, when suppressed, phenocopy BRAFV600E-induced arrest and converge on inhibition of AURKB to block cell cycle progression in primary human melanocytes.Statement of SignificanceWe describe a microRNA regulatory network that enforces BRAFV600E-induced growth arrest in human melanocytes during melanocytic nevus formation. De-regulation of MIR211-5p and MIR328-3p targets – which converge on AURKB – leads to cell cycle re-entry and melanoma progression. AURKB inhibition therefore provides a potential therapeutic intervention for melanoma prevention or treatment.

CDK1 phosphorylates ULK1-ATG13 complex to regulate mitotic autophagy and Taxol chemosensitivity

ULK1-ATG13 is the most upstream autophagy initiation complex that is phosphorylated by mTORC1 and AMPK to induce autophagy in asynchronous conditions. However, the phospho-regulation and function of ULK1-ATG13 in mitosis and cell cycle remains unknown. Here we show that ULK1-ATG13 complex is differentially regulated throughout the cell cycle. Notably, in mitosis, both ULK1 and ATG13 are highly phosphorylated by CDK1/cyclin B, the key cell cycle machinery. Combining mass spectrometry and site-directed mutagenesis, we found that CDK1-induced ULK1-ATG13 phosphorylation positively regulates mitotic autophagy and Taxol chemosensitivity, and some phosphorylation sites occur in cancer patients. Moreover, double knockout of ULK1 and ATG13 could block cell cycle progression and significantly decrease cancer cell proliferation in cell line and mouse models. Our results not only bridge the mutual regulation between the core machineries of autophagy and mitosis, illustrate the mitotic autophagy regulation mechanism, but also provide ULK1-ATG13 as potential targets for cancer therapy.

Gain-of-function mutations of PPM1D/Wip1 impair the p53-dependent G1 checkpoint

The DNA damage response (DDR) pathway and its core component tumor suppressor p53 block cell cycle progression after genotoxic stress and represent an intrinsic barrier preventing cancer development. The serine/threonine phosphatase PPM1D/Wip1 inactivates p53 and promotes termination of the DDR pathway. Wip1 has been suggested to act as an oncogene in a subset of tumors that retain wild-type p53. In this paper, we have identified novel gain-of-function mutations in exon 6 of PPM1D that result in expression of C-terminally truncated Wip1. Remarkably, mutations in PPM1D are present not only in the tumors but also in other tissues of breast and colorectal cancer patients, indicating that they arise early in development or affect the germline. We show that mutations in PPM1D affect the DDR pathway and propose that they could predispose to cancer.

Molecular Insight into How HIV-1 Vpr Protein Impairs Cell Growth through Two Genetically Distinct Pathways

Vpr, a small HIV auxiliary protein, hijacks the CUL4 ubiquitin ligase through DCAF1 to inactivate an unknown cellular target, leading to cell cycle arrest at the G2 phase and cell death. Here we first sought to delineate the Vpr determinants involved in the binding to DCAF1 and to the target. On the one hand, the three α-helices of Vpr are necessary and sufficient for binding to DCAF1; on the other hand, nonlinear determinants in Vpr are required for binding to the target, as shown by using protein chimeras. We also underscore that a SRIG motif conserved in the C-terminal tail of Vpr proteins from HIV-1/SIVcpz and HIV-2/SIVsmm lineages is critical for G2 arrest. Our results suggest that this motif may be predictive of the ability of Vpr proteins from other SIV lineages to mediate G2 arrest. We took advantage of the characterization of a subset of G2 arrest-defective, but DCAF1 binding-proficient mutants, to investigate whether Vpr interferes with cell viability independently of its ability to induce G2 arrest. These mutants inhibited cell colony formation in HeLa cells and are cytotoxic in lymphocytes, unmasking a G2 arrest-independent cytopathic effect of Vpr. Furthermore these mutants do not block cell cycle progression at the G1 or S phases but trigger apoptosis through caspase 3. Disruption of DCAF1 binding restored efficiency of colony formation. However, DCAF1 binding per se is not sufficient to confer cytopathicity. These data support a model in which Vpr recruits DCAF1 to induce the degradation of two host proteins independently required for proper cell growth.