Distinct functional classes of PDGFRB pathogenic variants in primary familial brain calcification.

Platelet-derived growth factor receptor beta (PDGFRB) is one of the genes associated with primary familial brain calcification (PFBC), an inherited neurological disease (OMIM:173410). Genetic analysis of patients and families revealed at least 13 PDGFRB heterozygous missense variants, including two novel ones described in the present report. Limited experimental data published on five of these variants had suggested that they decrease the receptor activity. No functional information was available on the impact of variants located within the receptor extracellular domains. Here, we performed a comprehensive molecular analysis of PDGFRB variants linked to PFBC. Mutated receptors were transfected in various cell lines to monitor receptor expression, signaling, mitogenic activity and ligand binding. Four mutants caused a complete loss of tyrosine kinase activity in multiple assays. One of the novel variants, p.Pro154Ser, decreased the receptor expression and abolished binding of platelet-derived growth factor (PDGF-BB). Others showed a partial loss of function related to reduced expression or signaling. Combining clinical, genetic and molecular data, we consider nine variants as pathogenic or likely pathogenic, three as benign or likely benign and one as a variant of unknown significance. We discuss the possible relationship between the variant residual activity, incomplete penetrance, brain calcification and neurological symptoms. In conclusion, we identified distinct molecular mechanisms whereby PDGFRB variants may result in a receptor loss of function. This work will facilitate genetic counseling in PFBC.

Gut microbiome alterations at acute myeloid leukemia diagnosis are associated with muscle weakness and anorexia.

The gut microbiota makes critical contributions to host homeostasis, and its role in the treatment of acute myeloid leukaemia (AML) has attracted attention. We investigated whether the gut microbiome is affected by AML, and whether such changes are associated with cachectic hallmarks. Biological samples and clinical data were collected from 30 antibiotic-free AML patients at diagnosis and matched volunteers (1:1) in a multicenter cross-sectional prospective study. The composition and functional potential of the faecal microbiota were analyzed using shotgun metagenomics. Faecal, blood, and urine metabolomics analyses were performed. AML patients displayed muscle weakness, anorexia, signs of altered gut function, and glycaemic disorders. The composition of the faecal microbiota differed between patients with AML and control subjects, with an increase in oral bacteria. Alterations in bacterial functions and faecal metabolome support an altered redox status in the gut microbiota, which may contribute to the altered redox status observed in patients with AML. Eubacterium eligens, reduced 3-fold in AML patients, was strongly correlated with muscle strength and citrulline, a marker of enterocyte mass and function. Blautia and Parabacteroides, increased in patients with AML, were correlated with anorexia. Several bacterial taxa and metabolites (e.g. Blautia, Prevotella, phenylacetate, and hippurate) previously associated with glycaemic disorders were altered. Our work revealed important perturbations in the gut microbiome of AML patients at diagnosis, which are associated with muscle strength, altered redox status, and anorexia. These findings pave the way for future mechanistic work to explore the function and therapeutic potential of the bacteria identified in this study.

Identification of a novel PHIP::BRAF gene fusion in infantile fibrosarcoma.

INTRODUCTION: The ETV6::NTRK3 fusion is the most common gene alteration in infantile fibrosarcoma, a soft tissue tumor affecting patients under two years of age. Less frequently, these tumors harbor fusions of genes encoding other kinases, such as BRAF, which activates MEK in the mitogen-activated protein kinase pathway. The identification and characterization of these oncogenes are crucial to facilitate diagnosis, validate new treatments, and better understand the pathophysiology of these neoplasms. METHODS: Herein, we analyzed an ETV6::NTRK3-negative infantile fibrosarcoma from a 5-day-old patient by RNA-sequencing to identify new fusion transcripts. Functional exploration of the fusion of interest was performed by in vitro assays to study its activity, oncogenicity, and sensitivity to the MEK inhibitor trametinib. RESULTS: We identified a novel fusion involving the PHIP and BRAF genes. The corresponding fusion protein constitutively activated the mitogen-activated protein kinase pathway, resulting in fibroblast transformation. Treatment of transfected cells with trametinib effectively inhibited signaling by PHIP::BRAF. CONCLUSION: PHIP::BRAF is a novel fusion oncogene that can be targeted by trametinib in infantile fibrosarcoma.

Penttinen syndrome-associated PDGFRB Val665Ala variant causes aberrant constitutive STAT1 signalling.

Penttinen syndrome is a rare progeroid disorder caused by mutations in platelet-derived growth factor (PDGF) receptor beta (encoded by the PDGFRB proto-oncogene) and characterized by a prematurely aged appearance with lipoatrophy, skin lesions, thin hair and acro-osteolysis. Activating mutations in PDGFRB have been associated with other human diseases, including Kosaki overgrowth syndrome, infantile myofibromatosis, fusiform aneurysms, acute lymphoblastic leukaemia and myeloproliferative neoplasms associated with eosinophilia. The goal of the present study was to characterize the PDGFRB p.Val665Ala variant associated with Penttinen syndrome at the molecular level. This substitution is located in a conserved loop of the receptor tyrosine kinase domain. We observed that the mutant receptor was expressed at a lower level but showed constitutive activity. In the absence of ligand, the mutant activated STAT1 and elicited an interferon-like transcriptional response. Phosphorylation of STAT3, STAT5, AKT and phospholipase Cγ was weak or undetectable. It was devoid of oncogenic activity in two cell proliferation assays, contrasting with classical PDGF receptor oncogenic mutants. STAT1 activation was not sensitive to ruxolitinib and did not rely on interferon-JAK2 signalling. Another tyrosine kinase inhibitor, imatinib, blocked signalling by the p.Val665Ala variant at a higher concentration compared with the wild-type receptor. Importantly, this concentration remained in the therapeutic range. Dasatinib, nilotinib and ponatinib also inhibited the mutant receptor. In conclusion, the p.Val665Ala variant confers unique features to PDGF receptor ß compared with other characterized gain-of-function mutants, which may in part explain the particular set of symptoms associated with Penttinen syndrome.

PDGF receptor mutations in human diseases.

PDGFRA and PDGFRB are classical proto-oncogenes that encode receptor tyrosine kinases responding to platelet-derived growth factor (PDGF). PDGFRA mutations are found in gastrointestinal stromal tumors (GISTs), inflammatory fibroid polyps and gliomas, and PDGFRB mutations drive myofibroma development. In addition, chromosomal rearrangement of either gene causes myeloid neoplasms associated with hypereosinophilia. Recently, mutations in PDGFRB were linked to several noncancerous diseases. Germline heterozygous variants that reduce receptor activity have been identified in primary familial brain calcification, whereas gain-of-function mutants are present in patients with fusiform aneurysms, Kosaki overgrowth syndrome or Penttinen premature aging syndrome. Functional analysis of these variants has led to the preclinical validation of tyrosine kinase inhibitors targeting PDGF receptors, such as imatinib, as a treatment for some of these conditions. This review summarizes the rapidly expanding knowledge in this field.

Novel COL4A1-VEGFD gene fusion in myofibroma.

Myofibroma is a benign pericytic tumour affecting young children. The presence of multicentric myofibromas defines infantile myofibromatosis (IMF), which is a life-threatening condition when associated with visceral involvement. The disease pathophysiology remains poorly characterized. In this study, we performed deep RNA sequencing on eight myofibroma samples, including two from patients with IMF. We identified five different in-frame gene fusions in six patients, including three previously described fusion transcripts, SRF-CITED1, SRF-ICA1L and MTCH2-FNBP4, and a fusion of unknown significance, FN1-TIMP1. We found a novel COL4A1-VEGFD gene fusion in two cases, one of which also carried a PDGFRB mutation. We observed a robust expression of VEGFD by immunofluorescence on the corresponding tumour sections. Finally, we showed that the COL4A1-VEGFD chimeric protein was processed to mature VEGFD growth factor by proteases, such as the FURIN proprotein convertase. In conclusion, our results unravel a new recurrent gene fusion that leads to VEGFD production under the control of the COL4A1 gene promoter in myofibroma. This fusion is highly reminiscent of the COL1A1-PDGFB oncogene associated with dermatofibrosarcoma protuberans. This work has implications for the diagnosis and, possibly, the treatment of a subset of myofibromas.

miR-15a-5p and miR-21-5p contribute to chemoresistance in cytogenetically normal acute myeloid leukaemia by targeting PDCD4, ARL2 and BTG2.

Cytarabine and daunorubicin are old drugs commonly used in the treatment of acute myeloid leukaemia (AML). Refractory or relapsed disease because of chemotherapy resistance is a major issue. microRNAs (miRNAs) were incriminated in resistance. This study aimed to identify miRNAs involved in chemoresistance in AML patients and to define their target genes. We focused on cytogenetically normal AML patients with wild-type NPM1 without FLT3-ITD as the treatment of this subset of patients with intermediate-risk cytogenetics is not well established. We analysed baseline AML samples by small RNA sequencing and compared the profile of chemoresistant to chemosensitive AML patients. Among the miRNAs significantly overexpressed in chemoresistant patients, we revealed miR-15a-5p and miR-21-5p as miRNAs with a major role in chemoresistance in AML. We showed that miR-15a-5p and miR-21-5p overexpression decreased apoptosis induced by cytarabine and/or daunorubicin. PDCD4, ARL2 and BTG2 genes were found to be targeted by miR-15a-5p, as well as PDCD4 and BTG2 by miR-21-5p. Inhibition experiments of the three target genes reproduced the functional effect of both miRNAs on chemosensitivity. Our study demonstrates that miR-15a-5p and miR-21-5p are overexpressed in a subgroup of chemoresistant AML patients. Both miRNAs induce chemoresistance by targeting three pro-apoptotic genes PDCD4, ARL2 and BTG2.

MiR-15a-5p Confers Chemoresistance in Acute Myeloid Leukemia by Inhibiting Autophagy Induced by Daunorubicin.

Anthracyclines remain a cornerstone of induction chemotherapy for acute myeloid leukemia (AML). Refractory or relapsed disease due to chemotherapy resistance is a major obstacle in AML management. MicroRNAs (miRNAs) have been observed to be involved in chemoresistance. We previously observed that miR-15a-5p was overexpressed in a subgroup of chemoresistant cytogenetically normal AML patients compared with chemosensitive patients treated with daunorubicin and cytarabine. MiR-15a-5p overexpression in AML cells reduced apoptosis induced by both drugs in vitro. This study aimed to elucidate the mechanisms by which miR-15a-5p contributes to daunorubicin resistance. We showed that daunorubicin induced autophagy in myeloid cell lines. The inhibition of autophagy reduced cell sensitivity to daunorubicin. The overexpression of miR-15a-5p decreased daunorubicin-induced autophagy. Conversely, the downregulation of miR-15a-5p increased daunorubicin-induced autophagy. We found that miR-15a-5p targeted four genes involved in autophagy, namely ATG9a, ATG14, GABARAPL1 and SMPD1. Daunorubicin increased the expression of these four genes, and miR-15a-5p counteracted this regulation. Inhibition experiments with the four target genes showed the functional effect of miR-15a-5p on autophagy. In summary, our results indicated that miR-15a-5p induces chemoresistance in AML cells through the abrogation of daunorubicin-induced autophagy, suggesting that miR-15a-5p could be a promising therapeutic target for chemoresistant AML patients.

The HMG box transcription factor HBP1: a cell cycle inhibitor at the crossroads of cancer signaling pathways.

HMG box protein 1 (HBP1) is a transcription factor and a potent cell cycle inhibitor in normal and cancer cells. HBP1 activates or represses the expression of different cell cycle genes (such as CDKN2A, CDKN1A, and CCND1) through direct DNA binding, cofactor recruitment, chromatin remodeling, or neutralization of other transcription factors. Among these are LEF1, TCF4, and MYC in the WNT/beta-catenin pathway. HBP1 also contributes to oncogenic RAS-induced senescence and terminal cell differentiation. Collectively, these activities suggest a tumor suppressor function. However, HBP1 is not listed among frequently mutated cancer driver genes. Nevertheless, HBP1 expression is lower in several tumor types relative to matched normal tissues. Several micro-RNAs, such as miR-155, miR-17-92, and miR-29a, dampen HBP1 expression in cancer cells of various origins. The phosphatidylinositol-3 kinase (PI3K)/AKT pathway also inhibits HBP1 transcription by preventing FOXO binding to the HBP1 promoter. In addition, AKT directly phosphorylates HBP1, thereby inhibiting its transcriptional activity. Taken together, these findings place HBP1 at the center of a network of micro-RNAs and oncoproteins that control cell proliferation. In this review, we discuss our current understanding of HBP1 function in human physiology and diseases.

PDGFRB gain-of-function mutations in sporadic infantile myofibromatosis.

Infantile myofibromatosis is one of the most prevalent soft tissue tumors of infancy and childhood. Multifocal nodules with visceral lesions are associated with a poor prognosis. A few familial cases have been linked to mutations in various genes including PDGFRB. In this study, we sequenced PDGFRB, which encodes a receptor tyrosine kinase, in 16 cases of myofibromatosis or solitary myofibroma. Mutations in the coding sequence of PDGFRB were identified in 6 out of 8 patients with the sporadic multicentric form of the disease and in 1 out of 8 patients with isolated myofibroma. Two patients had the same mutation in multiple separated lesions. By contrast, a third patient had three different PDGFRB mutations in the three nodules analyzed. Mutations were located in the transmembrane, juxtamembrane and kinase domains of the receptor. We showed that these mutations activated receptor signaling in the absence of ligand and transformed fibroblasts. In one case, a weakly-activating germline variant was associated with a stronger somatic mutation, suggesting a two-hit model for familial myofibromatosis. Furthermore, the mutant receptors were sensitive to the tyrosine kinase inhibitor imatinib, except D850V, which was inhibited by dasatinib and ponatinib, suggesting a targeted therapy for severe myofibromatosis. In conclusion, we identified gain-of-function PDGFRB mutations in the majority of multifocal infantile myofibromatosis cases, shedding light on the mechanism of disease development, which is reminiscent of multifocal venous malformations induced by TIE2 mutations. Our results provide a genetic test to facilitate diagnosis, and preclinical data for development of molecular therapies.

The gut microbiota metabolite indole alleviates liver inflammation in mice.

The gut microbiota regulates key hepatic functions, notably through the production of bacterial metabolites that are transported via the portal circulation. We evaluated the effects of metabolites produced by the gut microbiota from aromatic amino acids (phenylacetate, benzoate, p-cresol, and indole) on liver inflammation induced by bacterial endotoxin. Precision-cut liver slices prepared from control mice, Kupffer cell (KC)-depleted mice, and obese mice ( ob/ ob) were treated with or without LPS and bacterial metabolites. We observed beneficial effects of indole that dose-dependently reduced the LPS-induced up-regulation of proinflammatory mediators at both mRNA and protein levels in precision-cut liver slices prepared from control or ob/ ob mice. KC depletion partly prevented the antiinflammatory effects of indole, notably through a reduction of nucleotide-binding domain and leucine-rich repeat containing (NLR) family pyrin domain-containing 3 (NLRP3) pathway activation. In vivo, the oral administration of indole before an LPS injection reduced the expression of key proteins of the NF-κB pathway and downstream proinflammatory gene up-regulation. Indole also prevented LPS-induced alterations of cholesterol metabolism through a transcriptional regulation associated with increased 4ß-hydroxycholesterol hepatic levels. In summary, indole appears as a bacterial metabolite produced from tryptophan that is able to counteract the detrimental effects of LPS in the liver. Indole could be a new target to develop innovative strategies to decrease hepatic inflammation.-Beaumont, M., Neyrinck, A. M., Olivares, M., Rodriguez, J., de Rocca Serra, A., Roumain, M., Bindels, L. B., Cani, P. D., Evenepoel, P., Muccioli, G. G., Demoulin, J.-B., Delzenne, N. M. The gut microbiota metabolite indole alleviates liver inflammation in mice.

Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle.

We hypothesized that a single session of resistance exercise performed in moderate hypoxic (FiO2: 14%) environmental conditions would potentiate the anabolic response during the recovery period spent in normoxia. Twenty subjects performed a 1-leg knee extension session in normoxic or hypoxic conditions. Muscle biopsies were taken 15 min and 4 h after exercise in the vastus lateralis of the exercised and the nonexercised legs. Blood and saliva samples were taken at regular intervals before, during, and after the exercise session. The muscle fractional-protein synthetic rate was determined by deuterium incorporation into proteins, and the protein-degradation rate was determined by methylhistidine release from skeletal muscle. We found that: 1) hypoxia blunted the activation of protein synthesis after resistance exercise; 2) hypoxia down-regulated the transcriptional program of autophagy; 3) hypoxia regulated the expression of genes involved in glucose metabolism at rest and the genes involved in myoblast differentiation and fusion and in muscle contraction machinery after exercise; and 4) the hypoxia-inducible factor-1α pathway was not activated at the time points studied. Contrary to our hypothesis, environmental hypoxia did not potentiate the short-term anabolic response after resistance exercise, but it initiated transcriptional regulations that could potentially translate into satellite cell incorporation and higher force production in the long term.-Gnimassou, O., Fernández-Verdejo, R., Brook, M., Naslain, D., Balan, E., Sayda, M., Cegielski, J., Nielens, H., Decottignies, A., Demoulin, J.-B., Smith, K., Atherton, P. J., Fancaux, M., Deldicque, L. Environmental hypoxia favors myoblast differentiation and fast phenotype but blunts activation of protein synthesis after resistance exercise in human skeletal muscle.

Targeting the gut microbiota with inulin-type fructans: preclinical demonstration of a novel approach in the management of endothelial dysfunction.

OBJECTIVE: To investigate the beneficial role of prebiotics on endothelial dysfunction, an early key marker of cardiovascular diseases, in an original mouse model linking steatosis and endothelial dysfunction. DESIGN: We examined the contribution of the gut microbiota to vascular dysfunction observed in apolipoprotein E knockout (Apoe-/-) mice fed an n-3 polyunsaturated fatty acid (PUFA)-depleted diet for 12 weeks with or without inulin-type fructans (ITFs) supplementation for the last 15 days. Mesenteric and carotid arteries were isolated to evaluate endothelium-dependent relaxation ex vivo. Caecal microbiota composition (Illumina Sequencing of the 16S rRNA gene) and key pathways/mediators involved in the control of vascular function, including bile acid (BA) profiling, gut and liver key gene expression, nitric oxide and gut hormones production were also assessed. RESULTS: ITF supplementation totally reverses endothelial dysfunction in mesenteric and carotid arteries of n-3 PUFA-depleted Apoe-/- mice via activation of the nitric oxide (NO) synthase/NO pathway. Gut microbiota changes induced by prebiotic treatment consist in increased NO-producing bacteria, replenishment of abundance in Akkermansia and decreased abundance in bacterial taxa involved in secondary BA synthesis. Changes in gut and liver gene expression also occur upon ITFs suggesting increased glucagon-like peptide 1 production and BA turnover as drivers of endothelium function preservation. CONCLUSIONS: We demonstrate for the first time that ITF improve endothelial dysfunction, implicating a short-term adaptation of both gut microbiota and key gut peptides. If confirmed in humans, prebiotics could be proposed as a novel approach in the prevention of metabolic disorders-related cardiovascular diseases.

A patient with germ-line gain-of-function PDGFRB p.N666H mutation and marked clinical response to imatinib.

PurposeHeterozygous germ-line activating mutations in PDGFRB cause Kosaki and Penttinen syndromes and myofibromatosis. We describe a 10-year-old child with a germ-line PDGFRB p.N666H mutation who responded to the tyrosine kinase inhibitor imatinib by inhibition of PDGFRB.MethodsThe impact of p.N666H on PDGFRB function and sensitivity to imatinib was studied in cell culture.ResultsCells expressing the p.N666H mutation showed constitutive PDGFRB tyrosine phosphorylation. PDGF-independent proliferation was abolished by imatinib at 1 µM concentration. Patient fibroblasts showed constitutive receptor tyrosine phosphorylation that was also abrogated by imatinib with reduced proliferation of treated cells.This led to patient treatment with imatinib at 400 mg daily (340 mg/m2) for a year with objective improvement of debilitating hand and foot contractures, reduced facial coarseness, and significant improvement in quality of life. New small subcutaneous nodules developed, but remained stable. Transient leukopenia, neutropenia, and fatigue resolved without intervention; however, mildly decreased growth velocity resulted in reducing imatinib dose to 200 mg daily (170 mg/m2). The patient continues treatment with ongoing clinical response.ConclusionTo our knowledge, this is one of the first personalized treatments of a congenital disorder caused by a germ-line PDGF receptor mutation with a PDGFRB inhibitor.

Activating transcription factor 3 attenuates chemokine and cytokine expression in mouse skeletal muscle after exercise and facilitates molecular adaptation to endurance training.

Activating transcription factor (ATF)3 regulates the expression of inflammation-related genes in several tissues under pathological contexts. In skeletal muscle, atf3 expression increases after exercise, but its target genes remain unknown. We aimed to identify those genes and to determine the influence of ATF3 on muscle adaptation to training. Skeletal muscles of ATF3-knockout (ATF3-KO) and control mice were analyzed at rest, after exercise, and after training. In resting muscles, there was no difference between genotypes in enzymatic activities or fiber type. After exercise, a microarray analysis in quadriceps revealed ATF3 affects genes modulating chemotaxis and chemokine/cytokine activity. Quantitative PCR showed that the mRNA levels of chemokine C-C motif ligand (ccl)8 and chemokine C-X-C motif ligand (cxcl)13 were higher in quadriceps of ATF3-KO mice than in control mice. The same was observed for ccl9 and cxcl13 in soleus. Also in soleus, ccl2, interleukin (il)6, il1ß, and cluster of differentiation (cd)68 mRNA levels increased after exercise only in ATF3-KO mice. Endurance training increased the basal mRNA level of hexokinase-2, hormone sensitive lipase, glutathione peroxidase-1, and myosin heavy chain IIa in quadriceps of control mice but not in ATF3-KO mice. In summary, ATF3 attenuates the expression of inflammation-related genes after exercise and thus facilitates molecular adaptation to training.-Fernández-Verdejo, R., Vanwynsberghe, A. M., Essaghir, A., Demoulin, J.-B., Hai, T., Deldicque, L., Francaux, M. Activating transcription factor 3 attenuates chemokine and cytokine expression in mouse skeletal muscle after exercise and facilitates molecular adaptation to endurance training.

Germline CDKN2A/P16INK4A mutations contribute to genetic determinism of sarcoma.

BACKGROUND: Sarcomas are rare mesenchymal malignancies whose pathogenesis is poorly understood; both environmental and genetic risk factors could contribute to their aetiology. METHODS AND RESULTS: We performed whole-exome sequencing (WES) in a familial aggregation of three individuals affected with soft-tissue sarcoma (STS) without TP53 mutation (Li-Fraumeni-like, LFL) and found a shared pathogenic mutation in CDKN2A tumour suppressor gene. We searched for individuals with sarcoma among 474 melanoma-prone families with a CDKN2A-/+ genotype and for CDKN2A mutations in 190 TP53-negative LFL families where the index case was a sarcoma. Including the initial family, eight independent sarcoma cases carried a germline mutation in the CDKN2A/p16INK4A gene. In five out of seven formalin-fixed paraffin-embedded sarcomas, heterozygosity was lost at germline CDKN2A mutations sites demonstrating complete loss of function. As sarcomas are rare in CDKN2A/p16INK4A carriers, we searched in constitutional WES of nine carriers for potential modifying rare variants and identified three in platelet-derived growth factor receptor (PDGFRA) gene. Molecular modelling showed that two never-described variants could impact the PDGFRA extracellular domain structure. CONCLUSION: Germline mutations in CDKN2A/P16INK4A, a gene known to predispose to hereditary melanoma, pancreatic cancer and tobacco-related cancers, account also for a subset of hereditary sarcoma. In addition, we identified PDGFRA as a candidate modifier gene.

Hepatocyte MyD88 affects bile acids, gut microbiota and metabolome contributing to regulate glucose and lipid metabolism.

OBJECTIVE: To examine the role of hepatocyte myeloid differentiation primary-response gene 88 (MyD88) on glucose and lipid metabolism. DESIGN: To study the impact of the innate immune system at the level of the hepatocyte and metabolism, we generated mice harbouring hepatocyte-specific deletion of MyD88. We investigated the impact of the deletion on metabolism by feeding mice with a normal control diet or a high-fat diet for 8 weeks. We evaluated body weight, fat mass gain (using time-domain nuclear magnetic resonance), glucose metabolism and energy homeostasis (using metabolic chambers). We performed microarrays and quantitative PCRs in the liver. In addition, we investigated the gut microbiota composition, bile acid profile and both liver and plasma metabolome. We analysed the expression pattern of genes in the liver of obese humans developing non-alcoholic steatohepatitis (NASH). RESULTS: Hepatocyte-specific deletion of MyD88 predisposes to glucose intolerance, inflammation and hepatic insulin resistance independently of body weight and adiposity. These phenotypic differences were partially attributed to differences in gene expression, transcriptional factor activity (ie, peroxisome proliferator activator receptor-α, farnesoid X receptor (FXR), liver X receptors and STAT3) and bile acid profiles involved in glucose, lipid metabolism and inflammation. In addition to these alterations, the genetic deletion of MyD88 in hepatocytes changes the gut microbiota composition and their metabolomes, resembling those observed during diet-induced obesity. Finally, obese humans with NASH displayed a decreased expression of different cytochromes P450 involved in bioactive lipid synthesis. CONCLUSIONS: Our study identifies a new link between innate immunity and hepatic synthesis of bile acids and bioactive lipids. This dialogue appears to be involved in the susceptibility to alterations associated with obesity such as type 2 diabetes and NASH, both in mice and humans.

FOXO transcription factors in cancer development and therapy.

The forkhead box O (FOXO) transcription factors are considered as tumor suppressors that limit cell proliferation and induce apoptosis. FOXO gene alterations have been described in a limited number of human cancers, such as rhabdomyosarcoma, leukemia and lymphoma. In addition, FOXO proteins are inactivated by major oncogenic signals such as the phosphatidylinositol-3 kinase pathway and MAP kinases. Their expression is also repressed by micro-RNAs in multiple cancer types. FOXOs are mediators of the tumor response to various therapies. However, paradoxical roles of FOXOs in cancer progression were recently described. FOXOs contribute to the maintenance of leukemia-initiating cells in acute and chronic myeloid leukemia. These factors may also promote invasion and metastasis of subsets of colon and breast cancers. Resistance to treatment was also ascribed to FOXO activation in multiple cases, including targeted therapies. In this review, we discuss the complex role of FOXOs in cancer development and response to therapy.

Idiopathic basal ganglia calcification-associated PDGFRB mutations impair the receptor signalling.

Platelet-derived growth factors (PDGF) bind to two related receptor tyrosine kinases, which are encoded by the PDGFRA and PDGFRB genes. Recently, heterozygous PDGFRB mutations have been described in patients diagnosed with idiopathic basal ganglia calcification (IBGC or Fahr disease), a rare inherited neurological disorder. The goal of the present study was to determine whether these mutations had a positive or negative impact on the PDGFRB activity. We first showed that the E1071V mutant behaved like wild-type PDGFRB and may represent a polymorphism unrelated to IBGC. In contrast, the L658P mutant had no kinase activity and failed to activate any of the pathways normally stimulated by PDGF. The R987W mutant activated Akt and MAP kinases but did not induce the phosphorylation of signal transducer and activator of transcription 3 (STAT3) after PDGF stimulation. Phosphorylation of phospholipase Cγ was also decreased. Finally, we showed that the R987W mutant was more rapidly degraded upon PDGF binding compared to wild-type PDGFRB. In conclusion, PDGFRB mutations associated with IBGC impair the receptor signalling. PDGFRB loss of function in IBGC is consistent with recently described inactivating mutations in the PDGF-B ligand. These results raise concerns about the long-term safety of PDGF receptor inhibition by drugs such as imatinib.

The expression of the tumour suppressor HBP1 is down-regulated by growth factors via the PI3K/PKB/FOXO pathway.

Growth factors inactivate the FOXO (forkhead box O) transcription factors through PI3K (phosphoinositide 3-kinase) and PKB (protein kinase B). By comparing microarray data from multiple model systems, we identified HBP1 (high-mobility group-box protein 1) as a novel downstream target of this pathway. HBP1 mRNA was down-regulated by PDGF (platelet-derived growth factor), FGF (fibroblast growth factor), PI3K and PKB, whereas it was up-regulated by FOXO factors. This observation was confirmed in human and murine fibroblasts as well as in cell lines derived from leukaemia, breast adenocarcinoma and colon carcinoma. Bioinformatics analysis led to the identification of a conserved consensus FOXO-binding site in the HBP1 promoter. By luciferase activity assay and ChIP, we demonstrated that FOXO bound to this site and regulated the HBP1 promoter activity in a PI3K-dependent manner. Silencing of HBP1 by shRNA increased the proliferation of human fibroblasts in response to growth factors, suggesting that HBP1 limits cell growth. Finally, by analysing a transcriptomics dataset from The Cancer Genome Atlas, we observed that HBP1 expression was lower in breast tumours that had lost FOXO expression. In conclusion, HBP1 is a novel target of the PI3K/FOXO pathway and controls cell proliferation in response to growth factors.