Tumor suppressor FLCN inhibits tumorigenesis of a FLCN-null renal cancer cell line and regulates expression of key molecules in TGF-β signaling

<p>Abstract</p> <p>Background</p> <p>Germline mutations in the <it>FLCN </it>gene are responsible for the development of fibrofolliculomas, lung cysts and renal neoplasia in Birt-Hogg-Dube' (BHD) syndrome. The encoded protein folliculin (FLCN) is conserved across species but contains no classic motifs or domains and its function remains unknown. Somatic mutations or loss of heterozygosity in the remaining wild type copy of the <it>FLCN </it>gene have been found in renal tumors from BHD patients suggesting that <it>FLCN </it>is a classic tumor suppressor gene.</p> <p>Results</p> <p>To examine the tumor suppressor function of <it>FLCN</it>, wild-type or mutant <it>FLCN </it>(H255R) was stably expressed in a <it>FLCN-null </it>renal tumor cell line, UOK257, derived from a BHD patient. When these cells were injected into nude mice, tumor development was inversely dependent upon the level of wild-type <it>FLCN </it>expression. We identified genes that were differentially expressed in the cell lines with or without wild-type <it>FLCN</it>, many of which are involved in TGF-β signaling, including <it>TGF-β2 </it>(<it>TGFB2</it>)<it>, inhibin β A chain </it>(<it>INHBA</it>)<it>, thrombospondin 1 </it>(<it>THBS1</it>), <it>gremlin </it>(<it>GREM1</it>), and <it>SMAD3</it>. In support of the <it>in vitro </it>data, <it>TGFB2</it>, <it>INHBA</it>, <it>THBS1 </it>and <it>SMAD3 </it>expression levels were significantly lower in BHD-associated renal tumors compared with normal kidney tissue. Although receptor mediated SMAD phosphorylation was not affected, basal and maximal TGF-β-induced levels of <it>TGFB2</it>, <it>INHBA </it>and <it>SMAD7 </it>were dramatically reduced in <it>FLCN-null </it>cells compared with <it>FLCN</it>-restored cells. Secreted TGF-β2 and activin A (homo-dimer of INHBA) protein levels were also lower in <it>FLCN-null </it>cells compared with <it>FLCN</it>-restored cells. Consistent with a growth suppressive function, activin A (but not TGF-β2) completely suppressed anchorage-independent growth of <it>FLCN-null </it>UOK257 cells.</p> <p>Conclusions</p> <p>Our data demonstrate a role for <it>FLCN </it>in the regulation of key molecules in TGF-β signaling and confirm deregulation of their expression in BHD-associated renal tumors. Thus, deregulation of genes involved in TGF-β signaling by <it>FLCN </it>inactivation is likely to be an important step for tumorigenesis in BHD syndrome.</p

Intestinal Diffuse Large B-Cell Lymphoma in a Patient with Systemic Lupus Erythematosus

A 44-year-old Japanese woman with systemic lupus erythematosus (SLE) presented to our hospital with abdominal pain. Radiological and endoscopic examinations led to the diagnosis of diffuse large B-cell lymphoma of the jejunum, which was subsequently resected. Patients with SLE reportedly have an increased risk of non-Hodgkin lymphoma, as demonstrated by our patient. Hence, lymphoma should be considered in the differential diagnosis of neoplastic lesions emerging in SLE patients. In addition, flow cytometry using endoscopically biopsied fragments is useful for the immediate diagnosis of lymphoma, leading to timely and accurate preoperative staging

Pyridoxal in the Cerebrospinal Fluid May Be a Better Indicator of Vitamin B6–dependent Epilepsy Than Pyridoxal 5′-Phosphate

Background We aimed to demonstrate the biochemical characteristics of vitamin B6–dependent epilepsy, with a particular focus on pyridoxal 5′-phosphate and pyridoxal in the cerebrospinal fluid. Methods Using our laboratory database, we identified patients with vitamin B6–dependent epilepsy and extracted their data on the concentrations of pyridoxal 5′-phosphate, pyridoxal, pipecolic acid, α-aminoadipic semialdehyde, and monoamine neurotransmitters. We compared the biochemical characteristics of these patients with those of other epilepsy patients with low pyridoxal 5′-phosphate concentrations. Results We identified seven patients with pyridoxine-dependent epilepsy caused by an ALDH7A1 gene abnormality, two patients with pyridoxal 5′-phosphate homeostasis protein deficiency, and 28 patients with other epilepsies with low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. Cerebrospinal fluid pyridoxal and pyridoxal 5′-phosphate concentrations were low in patients with vitamin B6–dependent epilepsy but cerebrospinal fluid pyridoxal concentrations were not reduced in most patients with other epilepsies with low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. Increase in 3-O-methyldopa and 5-hydroxytryptophan was demonstrated in some patients with vitamin B6–dependent epilepsy, suggestive of pyridoxal 5′-phosphate deficiency in the brain. Conclusions Low cerebrospinal fluid pyridoxal concentrations may be a better indicator of pyridoxal 5′-phosphate deficiency in the brain in vitamin B6–dependent epilepsy than low cerebrospinal fluid pyridoxal 5′-phosphate concentrations. This finding is especially helpful in individuals with suspected pyridoxal 5′-phosphate homeostasis protein deficiency, which does not have known biomarkers

Inactivation of the FLCN Tumor Suppressor Gene Induces TFE3 Transcriptional Activity by Increasing Its Nuclear Localization

Germline mutations in a tumor suppressor gene FLCN lead to development of fibrofolliculomas, lung cysts and renal cell carcinoma (RCC) in Birt-Hogg-Dubé syndrome. TFE3 is a member of the MiTF/TFE transcription factor family and Xp11.2 translocations found in sporadic RCC involving TFE3 result in gene fusions and overexpression of chimeric fusion proteins that retain the C-terminal DNA binding domain of TFE3. We found that GPNMB expression, which is regulated by MiTF, was greatly elevated in renal cancer cells harboring either TFE3 translocations or FLCN inactivation. Since TFE3 is implicated in RCC, we hypothesized that elevated GPNMB expression was due to increased TFE3 activity resulting from the inactivation of FLCN.TFE3 knockdown reduced GPNMB expression in renal cancer cells harboring either TFE3 translocations or FLCN inactivation. Moreover, FLCN knockdown induced GPNMB expression in FLCN-restored renal cancer cells. Conversely, wildtype FLCN suppressed GPNMB expression in FLCN-null cells. FLCN inactivation was correlated with increased TFE3 transcriptional activity accompanied by its nuclear localization as revealed by elevated GPNMB mRNA and protein expression, and predominantly nuclear immunostaining of TFE3 in renal cancer cells, mouse embryo fibroblast cells, mouse kidneys and mouse and human renal tumors. Nuclear localization of TFE3 was associated with TFE3 post-translational modifications including decreased phosphorylation.Increased TFE3 activity is a downstream event induced by FLCN inactivation and is likely to be important for renal tumor development. This study provides an important novel mechanism for induction of TFE3 activity in addition to TFE3 overexpression resulting from Xp11.2 translocations, suggesting that TFE3 may be more broadly involved in tumorigenesis

Seventh BHD international symposium: recent scientific and clinical advancement.

The 7th Birt-Hogg-Dubé (BHD) International Symposium convened virtually in October 2021. The meeting attracted more than 200 participants internationally and highlighted recent findings in a variety of areas, including genetic insight and molecular understanding of BHD syndrome, structure and function of the tumor suppressor Folliculin (FLCN), therapeutic and clinical advances as well as patients' experiences living with this malady

Pitavastatin suppresses diethylnitrosamine-induced liver preneoplasms in male C57BL/KsJ-db/db obese mice

<p>Abstract</p> <p>Background</p> <p>Obesity and related metabolic abnormalities, including inflammation and lipid accumulation in the liver, play a role in liver carcinogenesis. Adipocytokine imbalances, such as decreased serum adiponectin levels, are also involved in obesity-related liver tumorigenesis. In the present study, we examined the effects of pitavastatin - a drug used for the treatment of hyperlipidemia - on the development of diethylnitrosamine (DEN)-induced liver preneoplastic lesions in C57BL/KsJ-<it>db/db </it>(<it>db/db</it>) obese mice.</p> <p>Methods</p> <p>Male <it>db/db </it>mice were administered tap water containing 40 ppm DEN for 2 weeks and were subsequently fed a diet containing 1 ppm or 10 ppm pitavastatin for 14 weeks.</p> <p>Results</p> <p>At sacrifice, feeding with 10 ppm pitavastatin significantly inhibited the development of hepatic premalignant lesions, foci of cellular alteration, as compared to that in the untreated group by inducing apoptosis, but inhibiting cell proliferation. Pitavastatin improved liver steatosis and activated the AMPK-α protein in the liver. It also decreased free fatty acid and aminotransferases levels, while increasing adiponectin levels in the serum. The serum levels of tumor necrosis factor (TNF)-α and the expression of <it>TNF-α </it>and <it>interleukin-6 </it>mRNAs in the liver were decreased by pitavastatin treatment, suggesting attenuation of the chronic inflammation induced by excess fat deposition.</p> <p>Conclusions</p> <p>Pitavastatin is effective in inhibiting the early phase of obesity-related liver tumorigenesis and, therefore, may be useful in the chemoprevention of liver cancer in obese individuals.</p

Increased Stathmin1 Expression in the Dentate Gyrus of Mice Causes Abnormal Axonal Arborizations

Pituitary adenylate cyclase-activating polypeptide (PACAP) is involved in multiple brain functions. To clarify the cause of abnormal behavior in PACAP deficient-mice, we attempted the identification of genes whose expression was altered in the dentate gyrus of PACAP-deficient mice using the differential display method. Expression of stathmin1 was up-regulated in the dentate gyrus at both the mRNA and protein levels. PACAP stimulation inhibited stathmin1 expression in PC12 cells, while increased stathmin1expression in neurons of the subgranular zone and in primary cultured hippocampal neurons induced abnormal arborization of axons. We also investigated the pathways involved in PACAP deficiency. Ascl1 binds to E10 box of the stathmin1 promoter and increases stathmin1 expression. Inhibitory bHLH proteins (Hes1 and Id3) were rapidly up-regulated by PACAP stimulation, and Hes1 could suppress Ascl1 expression and Id3 could inhibit Ascl1 signaling. We also detected an increase of stathmin1 expression in the brains of schizophrenic patients. These results suggest that up-regulation of stathmin1 in the dentate gyrus, secondary to PACAP deficiency, may create abnormal neuronal circuits that cause abnormal behavior

Blockade of interleukin-6 signaling inhibits the classic pathway and promotes an alternative pathway of macrophage activation after spinal cord injury in mice

Background Recent in vivo and in vitro studies in non-neuronal and neuronal tissues have shown that different pathways of macrophage activation result in cells with different properties. Interleukin (IL)-6 triggers the classically activated inflammatory macrophages (M1 phenotype), whereas the alternatively activated macrophages (M2 phenotype) are anti-inflammatory. The objective of this study was to clarify the effects of a temporal blockade of IL-6/IL-6 receptor (IL-6R) engagement, using an anti-mouse IL-6R monoclonal antibody (MR16-1), on macrophage activation and the inflammatory response in the acute phase after spinal cord injury (SCI) in mice. Methods MR16-1 antibodies versus isotype control antibodies or saline alone were administered immediately after thoracic SCI in mice. SC tissue repair was compared between the two groups by Luxol fast blue (LFB) staining for myelination and immunoreactivity for the neuronal markers growth-associated protein (GAP)-43 and neurofilament heavy 200 kDa (NF-H) and for locomotor function. The expression of T helper (Th)1 cytokines (interferon (IFN)-? and tumor necrosis factor-a) and Th2 cytokines (IL-4, IL-13) was determined by immunoblot analysis. The presence of M1 (inducible nitric oxide synthase (iNOS)-positive, CD16/32-positive) and M2 (arginase 1-positive, CD206-positive) macrophages was determined by immunohistology. Using flow cytometry, we also quantified IFN-? and IL-4 levels in neutrophils, microglia, and macrophages, and Mac-2 (macrophage antigen-2) and Mac-3 in M2 macrophages and microglia. Results LFB-positive spared myelin was increased in the MR16-1-treated group compared with the controls, and this increase correlated with enhanced positivity for GAP-43 or NF-H, and improved locomotor Basso Mouse Scale scores. Immunoblot analysis of the MR16-1-treated samples identified downregulation of Th1 and upregulation of Th2 cytokines. Whereas iNOS-positive, CD16/32-positive M1 macrophages were the predominant phenotype in the injured SC of non-treated control mice, MR16-1 treatment promoted arginase 1-positive, CD206-positive M2 macrophages, with preferential localization of these cells at the injury site. MR16-1 treatment suppressed the number of IFN-?-positive neutrophils, and increased the number of microglia present and their positivity for IL-4. Among the arginase 1-positive M2 macrophages, MR16-1 treatment increased positivity for Mac-2 and Mac-3, suggestive of increased phagocytic behavior. Conclusion The results suggest that temporal blockade of IL-6 signaling after SCI abrogates damaging inflammatory activity and promotes functional recovery by promoting the formation of alternatively activated M2 macrophages

MiT/TFE Family Renal Cell Carcinoma

The microphthalmia-associated transcription factor/transcription factor E (MiT/TFE) family of transcription factors are evolutionarily conserved, basic helix–loop–helix leucine zipper (bHLH-Zip) transcription factors, consisting of MITF, TFEB, TFE3, and TFEC. MiT/TFE proteins, with the exception of TFEC, are involved in the development of renal cell carcinoma (RCC). Most of the MiT/TFE transcription factor alterations seen in sporadic RCC cases of MiT family translocation renal cell carcinoma (tRCC) are chimeric proteins generated by chromosomal rearrangements. These chimeric MiT/TFE proteins retain the bHLH-Zip structures and act as oncogenic transcription factors. The germline variant of MITF p.E318K has been reported as a risk factor for RCC. E 318 is present at the SUMOylation consensus site of MITF. The p.E318K variant abrogates SUMOylation on K 316, which results in alteration of MITF transcriptional activity. Only a few cases of MITF p.E318K RCC have been reported, and their clinical features have not yet been fully described. It would be important for clinicians to recognize MITF p.E318K RCC and consider MITF germline testing for undiagnosed familial RCC cases. This review outlines the involvement of the MiT/TFE transcription factors in RCC, both in sporadic and hereditary cases. Further elucidation of the molecular function of the MiT/TFE family is necessary for better diagnosis and treatment of these rare diseases