PCLAF promotes neuroblastoma G1/S cell cycle progression via the E2F1/PTTG1 axis

PCLAF (PCNA clamp-associated factor), also known as PAF15/ KIAA0101, is overexpressed in most human cancers and is a predominant regulator of tumor progression. However, its biological function in neuroblastoma remains unclear. PCLAF is extremely overexpressed in neuroblastoma and is associated with poor prognosis. Through the analysis of various data sets, we found that the high expression of PCLAF is positively correlated with increased stage and high risk of neuroblastoma. Most importantly, knocking down PCLAF could restrict the proliferation of neuroblastoma cells in vitro and in vitro. By analyzing RNA-seq data, we found that the enrichment of cell cycle-related pathway genes was most significant among the differentially expressed downregulated genes after reducing the expression of PCLAF. In addition, PCLAF accelerated the G1/S transition of the neuroblastoma cell cycle by activating the E2F1/PTTG1 signaling pathway. In this study, we reveal the mechanism by which PCLAF facilitates cell cycle progression and recommend that the PCLAF/E2F1/PTTG1 axis is a therapeutic target in neuroblastoma.Subject terms: Cancer epigenetics, Cell growth     

E2F7 and E2F8 keep the E2F family in balance

An article by Li and colleagues (in this issue of Developmental Cell) shows that the atypical E2Fs, E2F7 and E2F8, are critical for mouse development. One of the important functions of these family members stems from a negative feedback loop in which E2F7 and E2F8 limit the expression of E2F1 and prevent E2F1-dependent apoptosis.     

DNA-damage response control of E2F7 and E2F8

Here, we report that the two recently identified E2F subunits, E2F7 and E2F8, are induced in cells treated with DNA-damaging agents where they have an important role in dictating the outcome of the DNA-damage response. The DNA-damage-dependent induction coincides with the binding of E2F7 and E2F8 to the promoters of certain E2F-responsive genes, most notably that of the E2F1 gene, in which E2F7 and E2F8 coexist in a DNA-binding complex. As a consequence, E2F7 and E2F8 repress E2F target genes, such as E2F1, and reducing the level of each subunit results in an increase in E2F1 expression and activity. Importantly, depletion of either E2F7 or E2F8 prevents the cell-cycle effects that occur in response to DNA damage. Thus, E2F7 and E2F8 act upstream of E2F1, and influence the ability of cells to undergo a DNA-damage response. E2F7 and E2F8, therefore, underpin the DNA-damage response.     

Up-regulation of MELK by E2F1 promotes the proliferation in cervical cancer cells

Cervical cancer is a common gynecologic cancer and a frequent cause of death. In this study, we investigated the role of MELK (maternal embryonic leucine zipper kinase) in cervical cancer. We found that HPV 18 E6/E7 promoted MELK expression by activating E2F1. MELK knockdown blocked cancer cells growth. Furthermore, we used MELK-8A to inhibit the kinase activity of MELK and caused the G2/M phase arrest of cancer cells. Under the treatment of inhibitors, Hela cells formed multipolar spindles and eventually underwent apoptosis. We also found that MELK is involved in protein translation and folding during cell division through the MELK interactome and the temporal proteomic analysis under inhibition with MELK-8A. Altogether, these results suggest that MELK may play a vital role in cancer cell proliferation and indicate a potential therapeutic target for cervical cancer.     

Prostaglandin E2 receptor in the myometrium: distribution in subcellular fractions

[³H]Prostaglandin (PG) E₂ bound specifically to several subcellular fractions from bovine myometrium. The binding was temperature dependent, rapid, and reversible. PGE₂ and PGE₁ competed for the [³H]PGE₂ binding site. The PGs inhibited in the following decreasing order: PGE₂ = PGE₁ ? PGF_2α > PGA₂ > PGF_1β > PGB₂. No competitive effect could be found for oxytocin. Scatchard analysis of the binding data were interpreted as showing a single high-affinity binding constant. There was no difference in the binding constant between the various fractions. The average molar dissociation constant was 2.74 ± 0.14 × 10^?9. Quantitative differences in the maximum number of binding sites were observed between fractions. One plasma membrane fraction contained 21.4 ± 2.3 × 10^?11 and the sarcoplasmic reticulum contained 11.2 ± 0.8 × 10^?11 mol binding sites/g. The results suggest that there is a high-affinity PGE₂ receptor present in both plasma membrane and sarcoplasmic reticulum.     

Cdk5 promotes synaptogenesis by regulating the subcellular distribution of the MAGUK family member CASK

Synaptogenesis is a highly regulated process that underlies formation of neural circuitry. Considerable work has demonstrated the capability of some adhesion molecules, such as SynCAM and Neurexins/Neuroligins, to induce synapse formation in vitro. Furthermore, Cdk5 gain of function results in an increased number of synapses in vivo. To gain a better understanding of how Cdk5 might promote synaptogenesis, we investigated potential crosstalk between Cdk5 and the cascade of events mediated by synapse-inducing proteins. One protein recruited to developing terminals by SynCAM and Neurexins/Neuroligins is the MAGUK family member CASK. We found that Cdk5 phosphorylates and regulates CASK distribution to membranes. In the absence of Cdk5-dependent phosphorylation, CASK is not recruited to developing synapses and thus fails to interact with essential presynaptic components. Functional consequences include alterations in calcium influx. Mechanistically, Cdk5 regulates the interaction between CASK and liprin-alpha. These results provide a molecular explanation of how Cdk5 can promote synaptogenesis.     

rtcisE2F promotes the self-renewal and metastasis of liver tumor-initiating cells via N6-methyladenosine-dependent E2F3/E2F6 mRNA stability

Liver cancer is highly heterogeneous,and the tumor tissue harbors a variety of cell types.Liver tumor initiating cells(TICs) well contribute to tumor heterogeneity and account for tumor initiation and metastasis,but the molecular mechanisms of liver TIC self-renewal are elusive.Here,we identified a functional read-through rt-circRNA,termed rtcisE2 F,that is highly expressed in liver cancer and liver TICs.rtcisE2 F plays essential roles in the self-renewal and activities of liver TICs.rtcisE2 F t...     

CHPF promotes gastric cancer tumorigenesis through the activation of E2F1

Chondroitin polymerizing factor (CHPF) is an important glycosyltransferase involved in the biosynthesis of chondroitin sulfate. However, the relationship between CHPF and gastric cancer has not been fully investigated. CHPF expression in gastric cancer tissues was detected by immunohistochemistry and correlated with gastric cancer patient prognosis. Cultured gastric cancer cells and human gastric epithelial cell line GES1 were used to investigate the effects of shCHPF and shE2F1 on the development and progression of gastric cancer by MTT, western blotting, flow cytometry analysis of cell apoptosis, colony formation, transwell and gastric cancer xenograft mouse models, in vitro and in vivo. In gastric cancer tissues, CHPF was found to be significantly upregulated, and its expression correlated with tumor infiltration and advanced tumor stage and shorter patient survival in gastric cancer. CHPF may promote gastric cancer development by regulating cell proliferation, colony formation, cell apoptosis and cell migration, while knockdown induced the opposite effects. Moreover, the results from in vivo experiments demonstrated that tumor growth was suppressed by CHPF knockdown. Additionally, E2F1 was identified as a potential downstream target of CHPF in the regulation of gastric cancer, and its knockdown decreased the CHPF-induced promotion of gastric cancer. Mechanistic study revealed that CHPF may regulate E2F1 through affecting UBE2T-mediated E2F1 ubiquitination. This study showed, for the first time, that CHPF is a potential prognostic indicator and tumor promoter in gastric cancer whose function is likely carried out through the regulation of E2F1.Subject terms: Gastric cancer, Cell biology     

SLC7A2 deficiency promotes hepatocellular carcinoma progression by enhancing recruitment of myeloid-derived suppressors cells

The main reason for poor prognosis in hepatocellular carcinoma (HCC) patients is high metastasis and recurrence. Cancer progression depends on a tumor-supportive microenvironment. Therefore, illustrating the mechanisms of tumor immunity in underlying HCC metastasis is essential. Here, we report a novel role of solute carrier family 7 member 2 (SLC7A2), a member of the solute carrier family, in HCC metastasis. The reduction of SLC7A2 was an independent and significant risk factor for the survival of HCC patients. Upregulation of SLC7A2 decreased HCC invasion and metastasis, whereas downregulation of SLC7A2 promoted HCC invasion and metastasis. We further found that deficient SLC7A2 medicated the upregulation of CXCL1 through PI3K/Akt/NF-kκB pathway to recruit myeloid-derived suppressor cells (MDSCs), exerting tumor immunosuppressive effect. Moreover, we found that G9a-mediated di-methylation of H3K9 (H3K9me2) silenced the expression of SLC7A2 to suppress HCC metastasis and immune escape. In conclusion, G9a-mediated silencing of SLC7A2 exerts unexpected functions in cancer metastasis by fostering a tumor-supportive microenvironment through CXCL1 secretion and MDSCs recruitment. Thus, SLC7A2 may provide new mechanistic insight into the cancer-promoting property of MDSCs.Subject terms: Cancer microenvironment, Cancer immunotherapy, Metastasis