Phosphoproteomic analysis identifies supervillin as an ERK3 substrate regulating cytokinesis and cell ploidy.

Extracellular signal-regulated kinase 3 (ERK3) is a poorly characterized member of the mitogen-activated protein (MAP) kinase family. Functional analysis of the ERK3 signaling pathway has been hampered by a lack of knowledge about the substrates and downstream effectors of the kinase. Here, we used large-scale quantitative phosphoproteomics and targeted gene silencing to identify direct ERK3 substrates and gain insight into its cellular functions. Detailed validation of one candidate substrate identified the gelsolin/villin family member supervillin (SVIL) as a bona fide ERK3 substrate. We show that ERK3 phosphorylates SVIL on Ser245 to regulate myosin II activation and cytokinesis completion in dividing cells. Depletion of SVIL or ERK3 leads to increased cytokinesis failure and multinucleation, a phenotype rescued by wild type SVIL but not by the non-phosphorylatable S245A mutant. Our results unveil a new function of the atypical MAP kinase ERK3 in cell division and the regulation of cell ploidy.

Reptin/RUVBL2 is required for hepatocyte proliferation in vivo, liver regeneration and homeostasis.

Previous studies have shown that Reptin is overexpressed in hepatocellular carcinoma and that it is necessary for in vitro proliferation and cell survival. However, its pathophysiological role in vivo remains unknown. We aimed to study the role of Reptin in hepatocyte proliferation after regeneration using a liver Reptin knock-out model (ReptinLKO ). Interestingly, hepatocyte proliferation is strongly impaired in ReptinLKO mice 36 h after partial hepatectomy, associated with a decrease of cyclin-A expression and mTORC1 and MAPK signalling, leading to an impaired liver regeneration. Moreover, in the ReptinLKO model, we have observed a progressive loss of Reptin invalidation associated with an atypical liver regeneration. Hypertrophic and proliferative hepatocytes gradually replace ReptinKO hypotrophic hepatocytes. To conclude, our results show that Reptin is required for hepatocyte proliferation in vivo and liver regeneration and that it plays a crucial role in hepatocyte survival and liver homeostasis.

Liver Reptin/RUVBL2 controls glucose and lipid metabolism with opposite actions on mTORC1 and mTORC2 signalling.

OBJECTIVE: The AAA+ ATPase Reptin is overexpressed in hepatocellular carcinoma and preclinical studies indicate that it could be a relevant therapeutic target. However, its physiological and pathophysiological roles in vivo remain unknown. This study aimed to determine the role of Reptin in mammalian adult liver. DESIGN AND RESULTS: We generated an inducible liver-specific Reptin knockout (RepinLKO ) mouse model. Following Reptin invalidation, mice displayed decreased body and fat mass, hypoglycaemia and hypolipidaemia. This was associated with decreased hepatic mTOR protein abundance. Further experiments in primary hepatocytes demonstrated that Reptin maintains mTOR protein level through its ATPase activity. Unexpectedly, loss or inhibition of Reptin induced an opposite effect on mTORC1 and mTORC2 signalling, with: (1) strong inhibition of hepatic mTORC1 activity, likely responsible for the reduction of hepatocytes cell size, for decreased de novo lipogenesis and cholesterol transcriptional programmes and (2) enhancement of mTORC2 activity associated with inhibition of the gluconeogenesis transcriptional programme and hepatic glucose production. Consequently, the role of hepatic Reptin in the pathogenesis of insulin resistance (IR) and non-alcoholic fatty liver disease consecutive to a high-fat diet was investigated. We found that Reptin deletion completely rescued pathological phenotypes associated with IR, including glucose intolerance, hyperglycaemia, hyperlipidaemia and hepatic steatosis. CONCLUSION: We show here that the AAA +ATPase Reptin is a regulator of mTOR signalling in the liver and global glucido-lipidic homeostasis. Inhibition of hepatic Reptin expression or activity represents a new therapeutic perspective for metabolic syndrome.

Reptin regulates insulin-stimulated Akt phosphorylation in hepatocellular carcinoma via the regulation of SHP-1/PTPN6.

Hepatocellular carcinoma (HCC) is the main primary cancer of the liver. Many studies have shown that insulin resistance is a risk factor for HCC. We previously discovered the overexpression and oncogenic role of the Reptin/RUVBL2 ATPase in HCC. Here, we found that Reptin silencing enhanced insulin sensitivity in 2 HCC cell lines, as shown by a large potentiation of insulin-induced AKT phosphorylation on Ser473 and Thr308, and of downstream signalling. Reptin silencing did not affect the tyrosine phosphorylation of the insulin receptor nor of IRS1, but it enhanced the tyrosine phosphorylation of the p85 subunit of PI3K. The expression of the SHP-1/PTPN6 phosphatase, which dephosphorylates p85, was reduced after Reptin depletion. Forced expression of SHP-1 restored a normal AKT phosphorylation after insulin treatment in cells where Reptin was silenced, demonstrating that the downregulation of SHP1 is mechanistically linked to increased Akt phosphorylation. In conclusion, we have uncovered a new function for Reptin in regulating insulin signalling in HCC cells via the regulation of SHP-1 expression. We suggest that the regulation of insulin sensitivity by Reptin contributes to its oncogenic action in the liver.

Corrigendum: Expression of Bioactive Chemerin by Keratinocytes Inhibits Late Stages of Tumor Development in a Chemical Model of Skin Carcinogenesis.

[This corrects the article DOI: 10.3389/fonc.2019.01253.].

Expression of Bioactive Chemerin by Keratinocytes Inhibits Late Stages of Tumor Development in a Chemical Model of Skin Carcinogenesis.

Chemerin is a multifunctional protein acting mainly through the G protein-coupled receptor ChemR23/CMKLR1/Chemerin1. Its expression is frequently downregulated in human tumors, including in melanoma and squamous cell carcinoma of the skin and anti-tumoral properties of chemerin were reported in mouse tumor graft models. In the present study, we report the development of spontaneous skin tumors in aged ChemR23-deficient mice. In order to test the potential therapeutic benefit of chemerin analogs, a transgenic model in which bioactive chemerin is over-expressed by basal keratinocytes was generated. These animals are characterized by increased levels of chemerin immunoreactivity and bioactivity in the skin and the circulation. In a chemical carcinogenesis model, papillomas developed later, were less numerous, and their progression to carcinomas was delayed. Temporal control of chemerin expression by doxycycline allowed to attribute its effects to late stages of carcinogenesis. The protective effects of chemerin were partly abrogated by ChemR23 invalidation. These results demonstrate that chemerin is able to delay very significantly tumor progression in a model that recapitulates closely the evolution of solid cancer types in human and suggest that the chemerin-ChemR23 system might constitute an interesting target for therapeutic intervention in the cancer field.

Alteration Analysis of Bone Marrow Mesenchymal Stromal Cells from De Novo Acute Myeloid Leukemia Patients at Diagnosis.

Bone marrow (BM)-derived mesenchymal stromal cells (MSCs) frequently display alterations in several hematologic disorders, such as acute lymphoid leukemia, acute myeloid leukemia (AML), and myelodysplastic syndromes. In acute leukemias, it is not clear whether MSC alterations contribute to the development of the malignant clone or whether they are simply the effect of tumor expansion on the microenvironment. We extensively investigated the characteristics of MSCs isolated from the BM of patients with de novo AML at diagnosis (L-MSCs) in terms of phenotype (gene and protein expression, apoptosis and senescence levels, DNA double-strand break formation) and functions (proliferation and clonogenic potentials, normal and leukemic hematopoiesis-supporting activity). We found that L-MSCs show reduced proliferation capacity and increased apoptosis levels compared with MSCs from healthy controls. Longer population doubling time in L-MSCs was not related to the AML characteristics at diagnosis (French-American-British type, cytogenetics, or tumor burden), but was related to patient age and independently associated with poorer patient outcome, as was cytogenetic prognostic feature. Analyzing, among others, the expression of 93 genes, we found that proliferative deficiency of L-MSCs was associated with a perivascular feature at the expense of the osteo-chondroblastic lineage with lower expression of several niche factors, such as KITLG, THPO, and ANGPT1 genes, the cell adhesion molecule VCAM1, and the developmental/embryonic genes, BMI1 and DICER1. L-MSC proliferative capacity was correlated positively with CXCL12, THPO, and ANGPT1 expression and negatively with JAG1 expression. Anyway, these changes did not affect their in vitro capacity to support normal hematopoiesis and to modify leukemic cell behavior (protection from apoptosis and quiescence induction). Our findings indicate that BM-derived MSCs from patients with newly diagnosed AML display phenotypic and functional alterations such as proliferative deficiency that could be attributed to tumor progression, but does not seem to play a special role in the leukemic process.

Reptin regulates DNA double strand breaks repair in human hepatocellular carcinoma.

Reptin/RUVBL2 is overexpressed in most hepatocellular carcinomas and is required for the growth and viability of HCC cells. Reptin is involved in several chromatin remodeling complexes, some of which are involved in the detection and repair of DNA damage, but data on Reptin involvement in the repair of DNA damage are scarce and contradictory. Our objective was to study the effects of Reptin silencing on the repair of DNA double-strand breaks (DSB) in HCC cells. Treatment of HuH7 cells with etoposide (25 µM, 30 min) or γ irradiation (4 Gy) increased the phosphorylation of H2AX by 1.94 ± 0.13 and 2.0 ± 0.02 fold, respectively. These values were significantly reduced by 35 and 65 % after Reptin silencing with inducible shRNA. Irradiation increased the number of BRCA1 (3-fold) and 53BP1 foci (7.5 fold). Depletion of Reptin reduced these values by 62 and 48%, respectively. These defects in activation and/or recruitment of repair proteins were not due to a decreased number of DSBs as measured by the COMET assay. All these results were confirmed in the Hep3B cell line. Protein expression of ATM and DNA-PKcs, the major H2AX kinases, was significantly reduced by 52 and 61 % after Reptin depletion whereas their mRNA level remained unchanged. Phosphorylation of Chk2, another ATM target, was not significantly altered. Using co-immunoprecipitation, we showed an interaction between Reptin and DNA-PKcs. The half-life of newly-synthesized DNA-PKcs was reduced when Reptin was silenced. Finally, depletion of Reptin was synergistic with etoposide or γ irradiation to reduce cell growth and colony formation. In conclusion, Reptin is an important cofactor for the repair of DSBs. Our data, combined with those of the literature suggests that it operates at least in part by regulating the expression of DNA-PKcs by a stabilization mechanism. Overexpression of Reptin in HCC could be a factor of resistance to treatment, consistent with the observed overexpression of Reptin in subgroups of chemo-resistant breast and ovarian cancers.