A pseudoautosomal glycosylation disorder prompts the revision of dolichol biosynthesis.

Dolichol is a lipid critical for N-glycosylation as a carrier for activated sugars and nascent oligosaccharides. It is commonly thought to be directly produced from polyprenol by the enzyme SRD5A3. Instead, we found that dolichol synthesis requires a three-step detour involving additional metabolites, where SRD5A3 catalyzes only the second reaction. The first and third steps are performed by DHRSX, whose gene resides on the pseudoautosomal regions of the X and Y chromosomes. Accordingly, we report a pseudoautosomal-recessive disease presenting as a congenital disorder of glycosylation in patients with missense variants in DHRSX (DHRSX-CDG). Of note, DHRSX has a unique dual substrate and cofactor specificity, allowing it to act as a NAD+-dependent dehydrogenase and as a NADPH-dependent reductase in two non-consecutive steps. Thus, our work reveals unexpected complexity in the terminal steps of dolichol biosynthesis. Furthermore, we provide insights into the mechanism by which dolichol metabolism defects contribute to disease.

SUZ domain-containing proteins have multiple effects on nonsense-mediated decay target transcripts.

Many transcripts are targeted by nonsense-mediated decay (NMD), leading to their degradation and the inhibition of their translation. We found that the protein SUZ domain-containing protein 1 (SZRD1) interacts with the key NMD factor up-frameshift 1. When recruited to NMD-sensitive reporter gene transcripts, SZRD1 increased protein production, at least in part, by relieving translational inhibition. The conserved SUZ domain in SZRD1 was required for this effect. The SUZ domain is present in only three other human proteins besides SZRD1: R3H domain-containing protein 1 and 2 (R3HDM1, R3HDM2) and cAMP-regulated phosphoprotein 21 (ARPP21). We found that ARPP21, similarly to SZRD1, can increase protein production from NMD-sensitive reporter transcripts in an SUZ domain-dependent manner. This indicated that the SUZ domain-containing proteins could prevent translational inhibition of transcripts targeted by NMD. Consistent with the idea that SZRD1 mainly prevents translational inhibition, we did not observe a systematic decrease in the abundance of NMD targets when we knocked down SZRD1. Surprisingly, knockdown of SZRD1 in two different cell lines led to reduced levels of the NMD component UPF3B, which was accompanied by increased levels in a subset of NMD targets. This suggests that SZRD1 is required to maintain normal UPF3B levels and indicates that the effect of SZRD1 on NMD targets is not limited to a relief from translational inhibition. Overall, our study reveals that human SUZ domain-containing proteins play a complex role in regulating protein output from transcripts targeted by NMD.

Senescence Induced by UVB in Keratinocytes Impairs Amino Acids Balance.

Skin is one of the most exposed organs to external stress. Namely, UV rays are the most harmful stress that could induce important damage leading to skin aging and cancers. At the cellular level, senescence is observed in several skin cell types and contributes to skin aging. However, the origin of skin senescent cells is still unclear but is probably related to exposure to stresses. In this work, we developed an in vitro model of UVB-induced premature senescence in normal human epidermal keratinocytes. UVB-induced senescent keratinocytes display a common senescent phenotype resulting in an irreversible cell cycle arrest, an increase in the proportion of senescence-associated ß-galactosidase‒positive cells, unrepaired DNA damage, and a long-term DNA damage response activation. Moreover, UVB-induced senescent keratinocytes secrete senescence-associated secretory phenotype factors that influence cutaneous squamous cell carcinoma cell migration. Finally, a global transcriptomic study highlighted that senescent keratinocytes present a decrease in the expression of several amino acid transporters, which is associated with reduced intracellular levels of glycine, alanine, and leucine. Interestingly, the chemical inhibition of the glycine transporter SLC6A9/Glyt1 triggers senescence features.

Parkinson's disease protein PARK7 prevents metabolite and protein damage caused by a glycolytic metabolite.

Cells are continuously exposed to potentially dangerous compounds. Progressive accumulation of damage is suspected to contribute to neurodegenerative diseases and aging, but the molecular identity of the damage remains largely unknown. Here we report that PARK7, an enzyme mutated in hereditary Parkinson's disease, prevents damage of proteins and metabolites caused by a metabolite of glycolysis. We found that the glycolytic metabolite 1,3-bisphosphoglycerate (1,3-BPG) spontaneously forms a novel reactive intermediate that avidly reacts with amino groups. PARK7 acts by destroying this intermediate, thereby preventing the formation of proteins and metabolites with glycerate and phosphoglycerate modifications on amino groups. As a consequence, inactivation of PARK7 (or its orthologs) in human cell lines, mouse brain, and Drosophila melanogaster leads to the accumulation of these damaged compounds, most of which have not been described before. Our work demonstrates that PARK7 function represents a highly conserved strategy to prevent damage in cells that metabolize carbohydrates. This represents a fundamental link between metabolism and a type of cellular damage that might contribute to the development of Parkinson's disease.

Loss of NFE2L3 protects against inflammation-induced colorectal cancer through modulation of the tumor microenvironment.

We investigated the role of the NFE2L3 transcription factor in inflammation-induced colorectal cancer. Our studies revealed that Nfe2l3-/- mice exhibit significantly less inflammation in the colon, reduced tumor size and numbers, and skewed localization of tumors with a more pronounced decrease of tumors in the distal colon. CIBERSORT analysis of RNA-seq data from normal and tumor tissue predicted a reduction in mast cells in Nfe2l3-/- animals, which was confirmed by toluidine blue staining. Concomitantly, the transcript levels of Il33 and Rab27a, both important regulators of mast cells, were reduced and increased, respectively, in the colorectal tumors of Nfe2l3-/- mice. Furthermore, we validated NFE2L3 binding to the regulatory sequences of the IL33 and RAB27A loci in human colorectal carcinoma cells. Using digital spatial profiling, we found that Nfe2l3-/- mice presented elevated FOXP3 and immune checkpoint markers CTLA4, TIM3, and LAG3, suggesting an increase in Treg counts. Staining for CD3 and FOXP3 confirmed a significant increase in immunosuppressive Tregs in the colon of Nfe2l3-/- animals. Also, Human Microbiome Project (HMP2) data showed that NFE2L3 transcript levels are higher in the rectum of ulcerative colitis patients. The observed changes in the tumor microenvironment provide new insights into the molecular differences regarding colon cancer sidedness. This may be exploited for the treatment of early-onset colorectal cancer as this emerging subtype primarily displays distal/left-sided tumors.

New Insights into CDK Regulators: Novel Opportunities for Cancer Therapy.

Cyclins and their catalytic partners, the cyclin-dependent kinases (CDKs), control the transition between different phases of the cell cycle. CDK/cyclin activity is regulated by CDK inhibitors (CKIs), currently comprising the CDK-interacting protein/kinase inhibitory protein (CIP/KIP) family and the inhibitor of kinase (INK) family. Recent studies have identified a third group of CKIs, called ribosomal protein-inhibiting CDKs (RPICs). RPICs were discovered in the context of cellular senescence, a stable cell cycle arrest with tumor-suppressing abilities. RPICs accumulate in the nonribosomal fraction of senescent cells due to a decrease in rRNA biogenesis. Accordingly, RPICs are often downregulated in human cancers together with other ribosomal proteins, the tumor-suppressor functions of which are still under study. In this review, we discuss unique therapies that have been developed to target CDK activity in the context of cancer treatment or senescence-associated pathologies, providing novel tools for precision medicine.

Transmembrane (TMEM) protein family members: Poorly characterized even if essential for the metastatic process.

The majority of cancer-associated deaths are related to secondary tumor formation. This multistep process involves the migration of cancer cells to anatomically distant organs. Metastasis formation relies on cancer cell dissemination and survival in the circulatory system, as well as adaptation to the new tissue notably through genetic and/or epigenetic alterations. A large number of proteins are clearly identified to play a role in the metastatic process but the structures and modes of action of these proteins are essentially unknown or poorly described. In this review, we detail the involvement of members of the transmembrane (TMEM) protein family in the formation of metastases or in the mechanisms leading to cancer cell dissemination such as migration and extra-cellular matrix remodelling. While the phenotype associated with TMEM over or down-expression is clear, the mechanisms by which these proteins allow cancer cell spreading remain, for most of them, unclear. In parallel, the 3D structures of these proteins are presented. Moreover, we proposed that TMEM proteins could be used as prognostic markers in different types of cancers and could represent potential targets for cancer treatment. A better understanding of this heterogeneous family of poorly characterized proteins thus opens perspectives for better cancer patient care.

NFE2L3 Controls Colon Cancer Cell Growth through Regulation of DUX4, a CDK1 Inhibitor.

Constitutive nuclear factor κB (NF-κB) activation is a hallmark of colon tumor growth. Cyclin-dependent kinases (CDKs) are critical cell-cycle regulators, and inhibition of CDK activity has been used successfully as anticancer therapy. Here, we show that the NFE2L3 transcription factor functions as a key regulator in a pathway that links NF-κB signaling to the control of CDK1 activity, thereby driving colon cancer cell proliferation. We found that NFE2L3 expression is regulated by the RELA subunit of NF-κB and that NFE2L3 levels are elevated in patients with colon adenocarcinoma when compared with normal adjacent tissue. Silencing of NFE2L3 significantly decreases colon cancer cell proliferation in vitro and tumor growth in vivo. NFE2L3 knockdown results in increased levels of double homeobox factor 4 (DUX4), which functions as a direct inhibitor of CDK1. The discovered oncogenic pathway governing cell-cycle progression may open up unique avenues for precision cancer therapy.

Phosphoglycolate has profound metabolic effects but most likely no role in a metabolic DNA response in cancer cell lines.

Repair of a certain type of oxidative DNA damage leads to the release of phosphoglycolate, which is an inhibitor of triose phosphate isomerase and is predicted to indirectly inhibit phosphoglycerate mutase activity. Thus, we hypothesized that phosphoglycolate might play a role in a metabolic DNA damage response. Here, we determined how phosphoglycolate is formed in cells, elucidated its effects on cellular metabolism and tested whether DNA damage repair might release sufficient phosphoglycolate to provoke metabolic effects. Phosphoglycolate concentrations were below 5 µM in wild-type U2OS and HCT116 cells and remained unchanged when we inactivated phosphoglycolate phosphatase (PGP), the enzyme that is believed to dephosphorylate phosphoglycolate. Treatment of PGP knockout cell lines with glycolate caused an up to 500-fold increase in phosphoglycolate concentrations, which resulted largely from a side activity of pyruvate kinase. This increase was much higher than in glycolate-treated wild-type cells and was accompanied by metabolite changes consistent with an inhibition of phosphoglycerate mutase, most likely due to the removal of the priming phosphorylation of this enzyme. Surprisingly, we found that phosphoglycolate also inhibits succinate dehydrogenase with a Ki value of <10 µM. Thus, phosphoglycolate can lead to profound metabolic disturbances. In contrast, phosphoglycolate concentrations were not significantly changed when we treated PGP knockout cells with Bleomycin or ionizing radiation, which are known to lead to the release of phosphoglycolate by causing DNA damage. Thus, phosphoglycolate concentrations due to DNA damage are too low to cause major metabolic changes in HCT116 and U2OS cells.

Senescence-associated ribosome biogenesis defects contributes to cell cycle arrest through the Rb pathway.

Cellular senescence is a tumour suppressor programme characterized by a stable cell cycle arrest. Here we report that cellular senescence triggered by a variety of stimuli leads to diminished ribosome biogenesis and the accumulation of both rRNA precursors and ribosomal proteins. These defects were associated with reduced expression of several ribosome biogenesis factors, the knockdown of which was also sufficient to induce senescence. Genetic analysis revealed that Rb but not p53 was required for the senescence response to altered ribosome biogenesis. Mechanistically, the ribosomal protein S14 (RPS14 or uS11) accumulates in the soluble non-ribosomal fraction of senescent cells, where it binds and inhibits CDK4 (cyclin-dependent kinase 4). Overexpression of RPS14 is sufficient to inhibit Rb phosphorylation, inducing cell cycle arrest and senescence. Here we describe a mechanism for maintaining the senescent cell cycle arrest that may be relevant for cancer therapy, as well as biomarkers to identify senescent cells.

Ophiobolin A, a sesterterpenoid fungal phytotoxin, displays higher in vitro growth-inhibitory effects in mammalian than in plant cells and displays in vivo antitumor activity.

Ophiobolin A, a sesterterpenoid produced by plant pathogenic fungi, was purified from the culture extract of Drechslera gigantea and tested for its growth-inhibitory activity in both plant and mammalian cells. Ophiobolin A induced cell death in Nicotiana tabacum L. cv. Bright Yellow 2 (TBY-2) cells at concentrations ≥10 µM, with the TBY-2 cells showing typical features of apoptosis-like cell death. At a concentration of 5 µM, ophiobolin A did not affect plant cell viability but prevented cell proliferation. When tested on eight cancer cell lines, concentrations <1 µM of ophiobolin A inhibited growth by 50% after 3 days of culture irrespective of their multidrug resistance (MDR) phenotypes and their resistance levels to pro-apoptotic stimuli. It is, thus, unlikely that ophiobolin A exerts these in vitro growth-inhibitory effects in cancer cells by activating pro-apoptotic processes. Highly proliferative human keratinocytes appeared more sensitive to the growth-inhibitory effects of ophiobolin A than slowly proliferating ones. Ophiobolin A also displayed significant antitumor activity at the level of mouse survival when assayed at 10 mg/kg in the B16F10 mouse melanoma model with lung pseudometastases. Ophiobolin A could, thus, represent a novel scaffold to combat cancer types that display various levels of resistance to pro-apoptotic stimuli and/or various MDR phenotypes.

Fusicoccin a, a phytotoxic carbotricyclic diterpene glucoside of fungal origin, reduces proliferation and invasion of glioblastoma cells by targeting multiple tyrosine kinases.

Glioblastoma multiforme (GBM) is a deadly cancer that possesses an intrinsic resistance to pro-apoptotic insults, such as conventional chemotherapy and radiotherapy, and diffusely invades the brain parenchyma, which renders it elusive to total surgical resection. We found that fusicoccin A, a fungal metabolite from Fusicoccum amygdali, decreased the proliferation and migration of human GBM cell lines in vitro, including several cell lines that exhibit varying degrees of resistance to pro-apoptotic stimuli. The data demonstrate that fusicoccin A inhibits GBM cell proliferation by decreasing growth rates and increasing the duration of cell division and also decreases two-dimensional (measured by quantitative video microscopy) and three-dimensional (measured by Boyden chamber assays) migration. These effects of fusicoccin A treatment translated into structural changes in actin cytoskeletal organization and a loss of GBM cell adhesion. Therefore, fusicoccin A exerts cytostatic effects but low cytotoxic effects (as demonstrated by flow cytometry). These cytostatic effects can partly be explained by the fact that fusicoccin inhibits the activities of a dozen kinases, including focal adhesion kinase (FAK), that have been implicated in cell proliferation and migration. Overexpression of FAK, a nonreceptor protein tyrosine kinase, directly correlates with the invasive phenotype of aggressive human gliomas because FAK promotes cell proliferation and migration. Fusicoccin A led to the down-regulation of FAK tyrosine phosphorylation, which occurred in both normoxic and hypoxic GBM cell culture conditions. In conclusion, the current study identifies a novel compound that could be used as a chemical template for generating cytostatic compounds designed to combat GBM.

N-(2-{3-[3,5-bis(trifluoromethyl)phenyl]ureido}ethyl)-glycyrrhetinamide (6b): a novel anticancer glycyrrhetinic acid derivative that targets the proteasome and displays anti-kinase activity.

18-ß-Glycyrrhetinic acid (GA; 1) and many of its derivatives are cytotoxic in cancer cells. The current study aims to characterize the anticancer effects of 17 novel 1 derivatives. On the basis of these studies, N-(2-{3-[3,5-bis(trifluoromethyl)phenyl]ureido}ethyl)-glycyrrhetinamide (6b) appeared to be the most potent compound, with IC(50)in vitro growth inhibitory concentrations in single-digit micromolarity in a panel of 8 cancer cell lines. Compound 6b is cytostatic and displays similar efficiency in apoptosis-sensitive versus apoptosis-resistant cancer cell lines through, at least partly, the inhibition of the activity of a cluster of a dozen kinases that are implicated in cancer cell proliferation and in the control of the actin cytoskeleton organization. Compound 6b also inhibits the activity of the 3 proteolytic units of the proteasome. Compound 6b thus represents an interesting hit from which future compounds could be derived to improve chemotherapeutic regimens that aim to combat cancers associated with poor prognoses.

In vitro anticancer activity, toxicity and structure-activity relationships of phyllostictine A, a natural oxazatricycloalkenone produced by the fungus Phyllosticta cirsii.

The in vitro anticancer activity and toxicity of phyllostictine A, a novel oxazatricycloalkenone recently isolated from a plant-pathogenic fungus (Phyllosticta cirsii) was characterized in six normal and five cancer cell lines. Phyllostictine A displays in vitro growth-inhibitory activity both in normal and cancer cells without actual bioselectivity, while proliferating cells appear significantly more sensitive to phyllostictine A than non-proliferating ones. The main mechanism of action by which phyllostictine displays cytotoxic effects in cancer cells does not seem to relate to a direct activation of apoptosis. In the same manner, phyllostictine A seems not to bind or bond with DNA as part of its mechanism of action. In contrast, phyllostictine A strongly reacts with GSH, which is a bionucleophile. The experimental data from the present study are in favor of a bonding process between GSH and phyllostictine A to form a complex though Michael attack at C=C bond at the acrylamide-like system. Considering the data obtained, two new hemisynthesized phyllostictine A derivatives together with three other natural phyllostictines (B, C and D) were also tested in vitro in five cancer cell lines. Compared to phyllostictine A, the two derivatives displayed a higher, phyllostictines B and D a lower, and phyllostictine C an almost equal, growth-inhibitory activity, respectively. These results led us to propose preliminary conclusions in terms of the structure-activity relationship (SAR) analyses for the anticancer activity of phyllostictine A and its related compounds, at least in vitro.

Evaluation of the anticancer activities of two fungal polycyclic ethanones, alternethanoxins A and B, and two of their derivatives.

Alternethanoxins A (1) and B (2) are fungal phytotoxins that are produced by Alternaria sonchi and have been recently characterized as new polycyclic ethanones. Triacetyl (3) and dimethyl (4) derivatives of compound 1 were evaluated together with alternethanoxins for their in vitro growth inhibitory activities in five human and one mouse cancer cell lines in comparison to the reference compound temozolomide (TMZ). Compounds 1-4 and TMZ displayed similar growth inhibitory activities, and these anticancer activities were equivalent in cancer cell lines that display certain levels of resistance to pro-apoptotic stimuli and those that are sensitive to pro-apoptotic stimuli. Of the six cancer cell lines under study, the human esophageal cancer cell line OE21 was the most sensitive to the four polycyclic ethanones. Computer-assisted phase-contrast microscopy (quantitative videomicroscopy) revealed that compounds 1, 2 and 4 displayed cytostatic rather than cytotoxic growth inhibitory effects, while compound 3 appeared to have cytotoxic effects. Thus, this study creates a stimulus for further structure-activity investigations with respect to the anticancer activities of compounds belonging to the alternethanoxin group. The observed toxicity does not seem to be affected by the stereochemistry of C-6 of the B ring, the presence of a hydroxy group at C-1 or the presence of a furan ring joining rings A and C in alternethanoxin B. The anticancer activity (cytostatic versus cytotoxic) of this type of compound could be affected by the chemical moieties present at the hydroxy groups at C-4 and C-6, as was observed for the cytostatic and cytotoxic activities of derivatives 4 and 3, respectively.