Balada E, etal., Autoimmunity. 2016;49(1):12-6. doi: 10.3109/08916934.2015.1113404. Epub 2015 Nov 22.
BACKGROUND: Overactivation of the interferon pathways has been demonstrated in patients suffering from different systemic autoimmune diseases (SADs). Genetic associations have been described for many genes involved in these pathways. Gain-of-function mutations in the TMEM17
MEM173 gene have recently been reported in patients with autoinflammatory diseases that share some clinical features with SADs. METHODS: We aimed at detecting the reported three mutations of transmembrane protein 173 (TMEM173) exon 5 in 100 patients suffering from: systemic lupus erythematosus (SLE) (n = 22), primary antiphospholipid syndrome (PAPS) (n = 20), systemic sclerosis (SSc) (n = 20), dermatomyositis (DM) (n = 20), and vasculitis (n = 18). Samples from 19 healthy controls were also included. Sequence analyses were performed from the derived TMEM173 exon 5 PCR fragment amplified from DNA obtained from whole blood. RESULTS: Neither mutations nor single nucleotide polymorphisms (SNPs) in the exon 5 of the TMEM173 gene were detected. Just the rs7380272 SNP, located in the intronic region upstream exon 5, was detected in some patients and controls. The allele frequency of this SNP, though, was not statistically different between the patients groups and the control group. CONCLUSIONS: Our study demonstrates the lack of association between the presence of SADs and mutations in exon 5 of the TMEM173 gene. SADs are complex multifactorial diseases in which not just one but probably many different genetic alterations may coexist. Although we cannot rule out the possibility that other variations may exist in other regions of this gene, we think that studies must be directed towards the analysis of other genes which, as TMEM173, also code for nucleic acid sensors that activate the nucleic-acid induced type I IFN pathway.
Decker CE, etal., Proc Natl Acad Sci U S A. 2015 Dec 22;112(51):15654-9. doi: 10.1073/pnas.1511285112. Epub 2015 Dec 7.
Phospholipase C gamma-2 (PLCgamma2)-dependent calcium (Ca(2+)) oscillations are indispensable for nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) activation and downstream gene transcription driving osteoclastogenesis during skeletal remodeling and pathological bone loss. Here we describ
e, to our knowledge, the first known function of transmembrane protein 178 (Tmem178), a PLCgamma2 downstream target gene, as a critical modulator of the NFATc1 axis. In surprising contrast to the osteopetrotic phenotype of PLCgamma2(-/-) mice, Tmem178(-/-) mice are osteopenic in basal conditions and are more susceptible to inflammatory bone loss, owing to enhanced osteoclast formation. Mechanistically, Tmem178 localizes to the ER membrane and regulates RANKL-induced Ca(2+) fluxes, thus controlling NFATc1 induction. Importantly, down-regulation of Tmem178 is observed in human CD14(+) monocytes exposed to plasma from systemic juvenile idiopathic arthritis patients. Similar to the mouse model, reduced Tmem178 expression in human cells correlates with excessive osteoclastogenesis. In sum, these findings identify an essential role for Tmem178 to maintain skeletal mass and limit pathological bone loss.
Rodríguez-García E, etal., Immunohorizons. 2018 Dec 11;2(11):363-376. doi: 10.4049/immunohorizons.1800068.
The innate immune system provides a primary line of defense against pathogens. Stimulator of IFN genes (STING), encoded by the TMEM173 gene, is a critical protein involved in IFN-β induction in response to infection by different pathogens. In this study, we desc
ribe the expression of three different alternative-spliced human (h) TMEM173 mRNAs producing STING truncated isoforms 1, 2, and 3 in addition to the full-length wild-type (wt) hSTING. All of the truncated isoforms lack exon 7 and share the N-terminal transmembrane region with wt hSTING. Overexpression of the three STING truncated isoforms failed to induce IFN-β, and they acted as selective pathway inhibitors of wt hSTING even in combination with upstream inducer cyclic-di-GMP-AMP synthase. Truncated isoforms alter the stability of wt hSTING, reducing protein t1/2 to some extent by the induction of proteasome-dependent degradation. Knocking down expression of truncated isoforms increased production of IFN-β by THP1 monocytes in response to intracellular cytosolic DNA or HSV-1 infection. At early stages of infection, viruses like HSV-1 or vesicular stomatitis virus reduced the ratio of full-length wt hSTING/truncated STING isoforms, suggesting the skewing of alternative splicing of STING toward truncated forms as a tactic to evade antiviral responses. Finally, in silico analysis revealed that the human intron-exon gene architecture of TMEM173 (splice sites included) is preserved in other mammal species, predominantly primates, stressing the relevance of alternative splicing in regulating STING antiviral biology.
Christodoulou A, etal., J Cell Sci. 2016 Feb 18. pii: jcs.175273.
The mechanism of endoplasmic reticulum (ER) morphogenesis is incompletely understood. ER tubules are shaped by the reticulons (RTNs) and DP1/Yop1p family members, but the mechanism of ER sheet formation is much less clear. Here we characterize TMEM170A, a human
transmembrane protein, which localizes in ER and NE membranes. Silencing or overexpressing TMEM170A in HeLa K cells alters ER shape and morphology. Ultrastructural analysis reveals that down-regulation of TMEM170A specifically induces tubular ER formation, while overexpression of TMEM170A induces ER sheet formation, indicating that TMEM170A is a novel ER sheet-promoting protein. Additionally, down-regulation of TMEM170A alters nuclear shape and size, decreases the density of nuclear pore complexes (NPCs) in the NE and causes either a reduction in inner nuclear membrane (INM) proteins or their relocalization to the ER. TMEM170A interacts with RTN4, a member of the reticulon family; simultaneous co-silencing of TMEM170A and RTN4 rescues ER, NPC and NE-related phenotypes, implying that the two proteins have antagonistic effects on ER membrane organization, NE and NPC formation.
Bu Y, etal., PLoS One. 2016 Nov 4;11(11):e0165681. doi: 10.1371/journal.pone.0165681. eCollection 2016.
Hepatocellular carcinoma (HCC) is one of the most lethal cancer types, and chronic infection with Hepatitis B Virus (HBV) is identified as the strongest risk factor for HCC. Transmembrane Protein 173 (TMEM173) is a pattern recognition receptor which functions as
a major regulator of the innate immune response to viral and bacterial infections. However, the prognostic value of TMEM173 in HCC remains elusive. Thus, we aimed to evaluate the potential prognostic significance of TMEM173 expression in HCC patients following curative resection. Immunohistochemistry was used to detect TMEM173 expression in 96 HCC patients. We found that TMEM173 protein expression was remarkably decreased in tumor tissues compared to non-tumor tissues, and that TMEM173 staining intensity was inversely correlated with tumor size, tumor invasion TNM stage and overall survival (OS) in HCC patients. Multivariate analysis supported TMEM173 as an independent prognostic factor, and identified that combining TMEM173 expression with TNM stage showed better prognostic efficiency for OS in HCC patients. In summary, TMEM173 was discovered having an independent prognostic value and may serve as a potential immunotherapeutic target for HCC.
Surpris G, etal., J Immunol. 2016 Jan 15;196(2):547-52. doi: 10.4049/jimmunol.1501415. Epub 2015 Dec 18.
With the stimulator of IFN genes (STING) C terminus being extensively studied, the role of the N-terminal domain (NTD) of STING remains an important subject of investigation. In this article, we identify novel mutations in NTD of Sting of the MOLF strain in response to HSV and Listeria monocytogene
s both in vitro and in vivo. These mutations are responsible for low levels of IFN-beta caused by failure of MOLF STING to translocate from the endoplasmic reticulum. These data provide evidence that the NTD of STING affects DNA responses via control of trafficking. They also show that the genetic diversity of wild-derived mice resembles the diversity observed in humans. Several human alleles of STING confer attenuated IFN-I production similar to what we observe with the MOLF Sting allele, a crucial functional difference not apparent in classical inbred mice. Thus, understanding the functional significance of polymorphisms in MOLF STING can provide basic mechanistic insights relevant to humans.
BACKGROUND: The proximal tubules play a critical role in phosphate (Pi) homeostasis by reabsorbing Pi via sodium-dependent Pi cotransporters. NPT2A is a major proximal-specific Pi cotransporter, whose expression is regulated by circulating hormones, such as parathyroid hormone (PTH) and f
ibroblast growth factor 23 (FGF23). In this study, we aimed to find a novel regulator in Pi homeostasis. METHODS: Using RNA-seq and RT-qPCR analysis, we identified proximal tubule cell-enriched genes. We next used RNAi screening of the identified proximal tubular cell-enriched genes to identify a novel proximal tubule-specific gene that contributes to FGF23- and PTH-mediated inhibition of Pi uptake and NPT2 reduction. We created mice lacking this novel regulator of Pi homeostasis to examine whether the novel regulator contributes to Pi homeostasis in vivo. RESULTS: We identified 54 kidney-enriched genes, 19 of which are expressed in renal primary proximal tubule cells. One of the proximal tubule-specific genes, TMEM174, interacted with NPT2A, and its knockdown blocked the reduction of NPT2A protein by FGF23 and PTH treatments in human and opossum proximal tubule cells. TMEM174 KO mice had significantly increased levels of serum Pi, FGF23, and PTH, resulting in vascular calcification. CONCLUSIONS: TMEM174 is a novel regulator of Pi homeostasis that interacts with NPT2A.
