Distinct Dynamic Modes Enable the Engagement of Dissimilar Ligands in a Promiscuous Atypical RNA Recognition Motif

Conformational dynamics play a critical role in ligand binding, often conferring divergent activities and specificities even in species with highly similar ground-state structures. Here, we employ time-resolved electrospray ionization hydrogen-deuterium exchange (TRESI-HDX) to characterize the changes in dynamics that accompany oligonucleotide binding in the atypical RNA recognition motif (RRM2) in the C-terminal domain (CTD) of human La protein. Using this approach, which is uniquely capable of probing changes in the structure and dynamics of weakly ordered regions of proteins, we reveal that binding of RRM2 to a model 23-mer single-stranded RNA and binding of RRM2 to structured IRES domain IV of the hepatitis C viral (HCV) RNA are driven by fundamentally different dynamic processes. In particular, binding of the single-stranded RNA induces helical "unwinding" in a region of the CTD previously hypothesized to play an important role in La and La-related protein-associated RNA remodeling, while the same region becomes less dynamic upon engagement with the double-stranded HCV RNA. Binding of double-stranded RNA also involves less penetration into the RRM2 binding pocket and more engagement with the unstructured C-terminus of the La CTD. The complementarity between TRESI-HDX and Δδ nuclear magnetic resonance measurements for ligand binding analysis is also explored.

Overexpression of LARP1 predicts poor prognosis of colorectal cancer and is expected to be a potential therapeutic target

This study investigated the significance of La-related protein 1 (LARP1) in the development and progression of colorectal cancer (CRC). Quantitative real-time polymerase chain reaction and Western blot analyses were carried out to determine the mRNA and protein expression of LARP1 in CRC tumor tissues and paired adjacent normal mucosa. The expression of LARP1 was upregulated in CRC. Immunohistochemical analysis using tissue microarray was performed. A positive correlation between LARP1 and proliferating cell nuclear antigen (PCNA) in the area of proliferation was observed using the Spearman's correlation coefficient test (r = 0.332, P < 0.01). The elevated expression of LARP1 significantly correlated with T stage (P = 0.02), N stage (P = 0.006), M stage (P < 0.001), American Joint Committee on Cancer (AJCC) stage (P = 0.04), differentiation rank (P < 0.001), and PCNA level (P < 0.001). In addition, the inhibitory effect of LARP1 knockdown on CRC cell proliferation was demonstrated using Cell Counting Kit-8 (CCK8) and colony-forming cell (CFC) assays. Multivariate analysis showed that LARP1 was an independent prognostic factor for overall survival (OS; hazard rate (HR) = 0.244; 95 % confidence interval (CI), 0.078-0.769; P = 0.016) and disease-free survival (DFS; HR = 0.281; 95 % CI, 0.086-0.917; P = 0.035) in CRC patients. LARP1 plays an important role in the proliferation of colorectal cancer and represents a new prognostic indicator.

The RNA-binding protein LARP4 regulates cancer cell migration and invasion

LARP4 is a La-related RNA-binding protein implicated in regulating mRNA translation, which interacts with poly(A)-binding protein (PABP). We previously identified LARP4 in an RNAi screen as one of several genes that regulate the shape of PC3 prostate cancer cells. Here we show that LARP4 depletion induces cell elongation in PC3 cells and MDA-MB-231 breast cancer cells. LARP4 depletion increases cell migration and invasion, as well as inducing invasive cell protrusions in 3D Matrigel. Conversely, LARP4 over-expression reduces cell elongation and increases cell circularity. LARP4 mutations are found in a variety of cancers. Introduction of some of these cancer-associated mutations, including a truncation mutant, into LARP4 enhances its effects on cell morphology. The truncation mutant shows enhanced interaction with PABP. We propose that LARP4 inhibits migration and invasion of cancer cells, and that some cancer-associated mutations stimulate these effects of LARP4. © 2016 The Authors. Cytoskeleton Published by Wiley Periodicals, Inc.

Plasmacytoid dendritic cells and type 1 interferon promote peripheral expansion of forkhead box protein 3(+) regulatory T cells specific for the ubiquitous RNA-binding nuclear antigen La/Sjögren's syndrome (SS)-B

RNA-binding nuclear antigens are a major class of self-antigen to which immune tolerance is lost in rheumatic diseases. Serological tolerance to one such antigen, La/Sjögren's syndrome (SS)-B (La), is controlled by CD4(+) T cells. This study investigated peripheral tolerance to human La (hLa) by tracking the fate of hLa-specific CD4(+) T cells expressing the transgenic (Tg) 3B5.8 T cell receptor (TCR) after adoptive transfer into lymphocyte-replete recipient mice expressing hLa as a neo-self-antigen. After initial antigen-specific cell division, hLa-specific donor CD4(+) T cells expressed forkhead box protein 3 (FoxP3). Donor cells retrieved from hLa Tg recipients displayed impaired proliferation and secreted interleukin (IL)-10 in vitro in response to antigenic stimulation. Transfer of highly purified FoxP3-negative donor cells demonstrated that accumulation of hLa-specific regulatory T cells (Treg ) was due primarily to expansion of small numbers of donor Treg . Depletion of recipient plasmacytoid dendritic cells (pDC), but not B cells, severely hampered the accumulation of FoxP3(+) donor Treg in hLa Tg recipients. Recipient pDC expressed tolerogenic markers and higher levels of co-stimulatory and co-inhibitory molecules than B cells. Adoptive transfer of hLa peptide-loaded pDC into mice lacking expression of hLa recapitulated the accumulation of hLa-specific Treg . Blockade of the type 1 interferon (IFN) receptor in hLa Tg recipients of hLa-specific T cells impaired FoxP3(+) donor T cell accumulation. Therefore, peripheral expansion of Treg specific for an RNA-binding nuclear antigen is mediated by antigen-presenting pDC in a type 1 IFN-dependent manner. These results reveal a regulatory function of pDC in controlling autoreactivity to RNA-binding nuclear antigens.

Analysis of the cell populations composing the mononuclear cell infiltrates in the labial minor salivary glands from patients with rheumatoid arthritis and sicca syndrome

OBJECTIVES

Sicca symptoms occur in around 30% of rheumatoid arthritis (RA) patients. Herein, we examined the characteristics of RA patients bearing sicca symptomatology (RA-sicca) with a special focus on the immunohistopathological features of their labial minor salivary gland (LMSG) biopsies.

METHODS

Our cohort included 100 consecutive RA patients which were interrogated using a sicca symptoms questionnaire. Positive responders were evaluated for ocular and oral dryness and underwent an LMSG biopsy. All samples were immunohistochemically evaluated for the presence and distribution of specific leukocyte subsets using appropriate markers and for the expression of certain immunoregulatory molecules by salivary gland epithelial cells. Positively stained and total mononuclear cells (MNC) were counted in the entire section. Counts were expressed as cell frequency (percentage of cell type number/total infiltrating MNC number).

RESULTS

In the majority (86.1%) of the 44 RA-sicca cases, periductal infiltrates were observed in LMSG biopsies. The frequencies of infiltrating cell subtypes and their correlation with lesion severity were different from that previously described in primary Sjögren's syndrome (pSS). Moreover, DCs and ΜΦs frequencies were increased in RA-sicca patients who had a biopsy focus score <1 and absence of anti-Ro/anti-La autoantibodies, in contrast to what was observed for B cells. In about half of the biopsies, salivary gland epithelial cells expressed CD80/B7.1 molecules, most commonly in patients with a positive biopsy or anti-Ro/anti-La autoantibodies.

CONCLUSION

LMSG infiltrates composition in RA-sicca patients is distinct from that described in pSS. These differences, further attest to diverse pathophysiologic processes operating in these two entities.

Association of anti-Ro52, anti-Ro60 and anti-La antibodies with diagnostic, clinical and laboratory features in a referral hospital in Jerez, Spain

OBJECTIVE

Several antibodies have proven to be useful in autoimmune diseases, as markers for diagnosis, prognosis or clinical manifestations. Our objective was to evaluate the diagnosis and manifestations associated for antibodies anti-Ro52, anti-Ro60 and anti-La at a referral hospital in Spain.

METHODS

We retrospectively analyzed the antigenic specificities of the consecutive samples submitted to the Immunology Unit for antinuclear antibody screening between 2002 and 2012. We included patients with more than one positive sample for some of the autoantibodies anti-Ro52, anti-Ro60 or anti-La. We also reviewed diagnosis, clinical and laboratory features. As dependent variable we evaluated possible combinations of anti-Ro52, anti-Ro60 and anti-La.

RESULTS

322 patients, 91% females, were studied (age 44.3±15.51 years). The most frequent diagnosis was Sjögren's syndrome (40.06%) and systemic lupus erythematosus (SLE) (36.6%). The most prevalent pattern by indirect immunofluorescence was the fine speckled (69.9%). Anti-Ro52+/anti-Ro60+/anti-La+ combination was positively associated with fine speckled pattern (p: 0.001) and negatively with homogeneous (p: 0.016) and cytoplasmic pattern (p: 0.002). Isolated anti-Ro52+ was negatively associated with fine speckled pattern (p<0.001) and positively with the cytoplasmic one (p<0.001). The main positive associations with clinical symptoms were xerostomia and xerophthalmia with anti-Ro52+/anti-Ro60+/anti-La+ (p<0.001), oral ulcers with anti-Ro52+/anti-Ro60+/anti-La- (p: 0.002) and alopecia with anti-Ro52-/anti-Ro60+/anti-La- (p: 0.003). Negative associations were xerophthalmia and photosensitivity with anti-Ro52+/anti-Ro60-/anti-La- (p: 0.003). Laboratory positive associations were hypergammaglobulinemia with anti-Ro52+/anti-Ro60+/anti-La+ (p: 0.003), and hypocomplementemia with anti-Ro52-/anti-Ro60+/anti-La- (p: 0.003). Leucopenia was negatively associated with anti-Ro52+/anti-Ro60-/anti-La- (p: 0.003).

CONCLUSION

Our study found significant relationships between clinical and laboratory manifestations with different patterns of antibodies to anti-Ro52, anti-Ro60 and anti-La. The combination of antibodies might be clinically useful due to prognostic and therapeutic implications.

La Autoantigen Induces Ribosome Binding Protein 1 (RRBP1) Expression through Internal Ribosome Entry Site (IRES)-Mediated Translation during Cellular Stress Condition

The function of ribosome binding protein 1 (RRBP1) is regulating the transportation and secretion of some intracellular proteins in mammalian cells. Transcription of RRBP1 is induced by various cytokines. However, few studies focused on the process of RRPB1 mRNA translation. The RRBP1 mRNA has a long 5' untranslated region that potentially formed a stable secondary structure. In this study, we show that the 5' UTR of RRBP1 mRNA contains an internal ribosome entry site (IRES). Moreover, the RRBP1 expression is induced by chemotherapeutic drug paclitaxel or adriamycin in human hepatocellular carcinoma cells and accompanied with the increased expression of La autoantigen (La), which binds to RRBP1 IRES element and facilitates translation initiation. Interestingly, we found IRES-mediated RRBP1 translation is also activated during serum-starvation condition which can induce cytoplasmic localization of La. After mapping the entire RRBP1 5' UTR, we determine the core IRES activity is located between nt-237 and -58. Furthermore, two apical GARR loops within the functional RRBP1 IRES elements may be important for La binding. These results strongly suggest an important role for IRES-dependent translation of RRBP1 mRNA in hepatocellular carcinoma cells during cellular stress conditions.

The Lupus Autoantigen La Prevents Mis-channeling of tRNA Fragments into the Human MicroRNA Pathway

The Lupus autoantigen La is an RNA-binding protein that stabilizes RNA polymerase III (Pol III) transcripts and supports RNA folding and has in addition been implicated in the mammalian microRNA (miRNA) pathway. Here, we have analyzed effects of La depletion on Argonaute (Ago)-bound small RNAs in human cells. We find that in the absence of La, distinct tRNA fragments are loaded into Ago proteins. Thus, La functions as gatekeeper ensuring correct tRNA maturation and protecting the miRNA pathway from potentially functional tRNA fragments. However, one specific isoleucin pre-tRNA produces both a functional tRNA and a miRNA even when La is present. We demonstrate that the fully complementary 5' leader and 3' trailer of the pre-tRNA-Ile form a double-stranded RNA molecule that has low affinity to La. Instead, Exportin-5 (Xpo5) recognizes it as miRNA precursor and transports it into the cytoplasm for Dicer processing and Ago loading.

Comparison of antibody assays for detection of autoantibodies to Ro 52, Ro 60 and La associated with primary Sjögren's syndrome

Anti-Ro(52/60) and anti-La constitute the hallmark autoantibodies in primary Sjögren's syndrome, being present in 40-70% of sera. Several anti-Ro/La assays exist, but antibody detection appears to be assay-specific, thus the aim of this study was to compare several anti-Ro/La assays. In total, 96 sera from individuals with primary Sjögren's syndrome and 114 healthy controls were tested for anti-Ro 52/60 and anti-La in 17 immunoassays. Especially the immunoassays used for detection of anti-Ro 52 differed in their sensitivity (48-79%), while only small differences in sensitivities were observed for the anti-Ro 60 (69-77%) anti-La (39-44%) assays. Concordances of 65%, 79% and 73% for the anti-Ro 52, anti-Ro 60 and anti-La assays were found, respectively. The majority of the assays yielded high specificities, primarily ranging from 97 to 100%, except from a single anti-Ro 60 assay, which yielded a specificity of 79%. Occasionally, reactivity levels were increased in a few assays, indicating that false-positive results can be obtained when applying assays of reduced specificity. In general, the commercial assays appeared to perform better than the in-house analyses. When correcting the in-house assays for background reactivity, sensitivities were reduced by approximately 7%, 17%, and 19% for anti-Ro 52, anti-Ro 60 and anti-La assays, respectively, illustrating the pitfalls when applying immunoassays for detection of autoantibodies, which in theory may apply to commercial assays as well. Finally, increased total sensitivities were obtained when combining assays. These studies contribute to clarify the clinical utility of immunoassays for detection of autoantibodies of Ro 52, Ro 60 and La and illustrate that the most efficient strategy to maximize antibody sensitivity is to combine several assays.

Identification of RNA-Binding Protein LARP4B as a Tumor Suppressor in Glioma

Transposon-based insertional mutagenesis is a valuable method for conducting unbiased forward genetic screens to identify cancer genes in mice. We used this system to elucidate factors involved in the malignant transformation of neural stem cells into glioma-initiating cells. We identified an RNA-binding protein, La-related protein 4b (LARP4B), as a candidate tumor-suppressor gene in glioma. LARP4B expression was consistently decreased in human glioma stem cells and cell lines compared with normal neural stem cells. Moreover, heterozygous deletion of LARP4B was detected in nearly 80% of glioblastomas in The Cancer Genome Atlas database. LARP4B loss was also associated with low expression and poor patient survival. Overexpression of LARP4B in glioma cell lines strongly inhibited proliferation by inducing mitotic arrest and apoptosis in four of six lines as well as in two patient-derived glioma stem cell populations. The expression levels of CDKN1A and BAX were also upregulated upon LARP4B overexpression, and the growth-inhibitory effects were partially dependent on p53 (TP53) activity in cells expressing wild-type, but not mutant, p53. We further found that the La module, which is responsible for the RNA chaperone activity of LARP4B, was important for the growth-suppressive effect and was associated with BAX mRNA. Finally, LARP4B depletion in p53 and Nf1-deficient mouse primary astrocytes promoted cell proliferation and led to increased tumor size and invasiveness in xenograft and orthotopic models. These data provide strong evidence that LARP4B serves as a tumor-suppressor gene in glioma, encouraging further exploration of the RNA targets potentially involved in LARP4B-mediatd growth inhibition. Cancer Res; 76(8); 2254-64. ©2016 AACR.

LARP6 Meets Collagen mRNA: Specific Regulation of Type I Collagen Expression

Type I collagen is the most abundant structural protein in all vertebrates, but its constitutive rate of synthesis is low due to long half-life of the protein (60-70 days). However, several hundred fold increased production of type I collagen is often seen in reparative or reactive fibrosis. The mechanism which is responsible for this dramatic upregulation is complex, including multiple levels of regulation. However, posttranscriptional regulation evidently plays a predominant role. Posttranscriptional regulation comprises processing, transport, stabilization and translation of mRNAs and is executed by RNA binding proteins. There are about 800 RNA binding proteins, but only one, La ribonucleoprotein domain family member 6 (LARP6), is specifically involved in type I collagen regulation. In the 5'untranslated region (5'UTR) of mRNAs encoding for type I and type III collagens there is an evolutionally conserved stem-loop (SL) structure; this structure is not found in any other mRNA, including any other collagen mRNA. LARP6 binds to the 5'SL in sequence specific manner to regulate stability of collagen mRNAs and their translatability. Here, we will review current understanding of how is LARP6 involved in posttranscriptional regulation of collagen mRNAs. We will also discuss how other proteins recruited by LARP6, including nonmuscle myosin, vimentin, serine threonine kinase receptor associated protein (STRAP), 25 kD FK506 binding protein (FKBP25) and RNA helicase A (RHA), contribute to this process.

Akt mediated phosphorylation of LARP6; critical step in biosynthesis of type I collagen

La ribonucleoprotein domain family, member 6 (LARP6) is the RNA binding protein, which regulates translation of collagen mRNAs and synthesis of type I collagen. Posttranslational modifications of LARP6 and how they affect type I collagen synthesis have not been studied. We show that in lung fibroblasts LARP6 is phosphorylated at 8 serines, 6 of which are located within C-terminal domain. Phosphorylation of LARP6 follows a hierarchical order; S451 phosphorylation being a prerequisite for phosphorylations of other serines. Inhibition of PI3K/Akt pathway reduced the phosphorylation of LARP6, but had no effect on the S451A mutant, suggesting that PI3K/Akt pathway targets S451 and we have identified Akt as the responsible kinase. Overexpression of S451A mutant had dominant negative effect on collagen biosynthesis; drastically reduced secretion of collagen and induced hyper-modifications of collagen α2 (I) polypeptides. This indicates that LARP6 phosphorylation at S451 is critical for regulating translation and folding of collagen polypeptides. Akt inhibitor, GSK-2141795, which is in clinical trials for treatment of solid tumors, reduced collagen production by human lung fibroblasts with EC50 of 150 nM. This effect can be explained by inhibition of LARP6 phosphorylation and suggests that Akt inhibitors may be effective in treatment of various forms of fibrosis.

Epidermal Growth Factor Receptor-Dependent Mutual Amplification between Netrin-1 and the Hepatitis C Virus

Hepatitis C virus (HCV) is an oncogenic virus associated with the onset of hepatocellular carcinoma (HCC). The present study investigated the possible link between HCV infection and Netrin-1, a ligand for dependence receptors that sustains tumorigenesis, in particular in inflammation-associated tumors. We show that Netrin-1 expression is significantly elevated in HCV+ liver biopsies compared to hepatitis B virus (HBV+) and uninfected samples. Furthermore, Netrin-1 was upregulated in all histological stages of HCV+ hepatic lesions, from minimal liver fibrosis to cirrhosis and HCC, compared to histologically matched HCV- tissues. Both cirrhosis and HCV contributed to the induction of Netrin-1 expression, whereas anti-HCV treatment resulted in a reduction of Netrin-1 expression. In vitro, HCV increased the level and translation of Netrin-1 in a NS5A-La-related protein 1 (LARP1)-dependent fashion. Knockdown and forced expression experiments identified the receptor uncoordinated receptor-5 (UNC5A) as an antagonist of the Netrin-1 signal, though it did not affect the death of HCV-infected cells. Netrin-1 enhanced infectivity of HCV particles and promoted viral entry by increasing the activation and decreasing the recycling of the epidermal growth factor receptor (EGFR), a protein that is dysregulated in HCC. Netrin-1 and HCV are, therefore, reciprocal inducers in vitro and in patients, as seen from the increase in viral morphogenesis and viral entry, both phenomena converging toward an increase in the level of infectivity of HCV virions. This functional association involving a cancer-related virus and Netrin-1 argues for evaluating the implication of UNC5 receptor ligands in other oncogenic microbial species.

The RNA-binding protein LARP1 is a post-transcriptional regulator of survival and tumorigenesis in ovarian cancer

RNA-binding proteins (RBPs) are increasingly identified as post-transcriptional drivers of cancer progression. The RBP LARP1 is an mRNA stability regulator, and elevated expression of the protein in hepatocellular and lung cancers is correlated with adverse prognosis. LARP1 associates with an mRNA interactome that is enriched for oncogenic transcripts. Here we explore the role of LARP1 in epithelial ovarian cancer, a disease characterized by the rapid acquisition of resistance to chemotherapy through the induction of pro-survival signalling. We show, using ovarian cell lines and xenografts, that LARP1 is required for cancer cell survival and chemotherapy resistance. LARP1 promotes tumour formation in vivo and maintains cancer stem cell-like populations. Using transcriptomic analysis following LARP1 knockdown, cross-referenced against the LARP1 interactome, we identify BCL2 and BIK as LARP1 mRNA targets. We demonstrate that, through an interaction with the 3' untranslated regions (3' UTRs) of BCL2 and BIK, LARP1 stabilizes BCL2 but destabilizes BIK with the net effect of resisting apoptosis. Together, our data indicate that by differentially regulating the stability of a selection of mRNAs, LARP1 promotes ovarian cancer progression and chemotherapy resistance.

LARP4 Is Regulated by Tumor Necrosis Factor Alpha in a Tristetraprolin-Dependent Manner

LARP4 is a protein with unknown function that independently binds to poly(A) RNA, RACK1, and the poly(A)-binding protein (PABPC1). Here, we report on its regulation. We found a conserved AU-rich element (ARE) in the human LARP4 mRNA 3' untranslated region (UTR). This ARE, but not its antisense version or a point-mutated version, significantly decreased the stability of β-globin reporter mRNA. We found that overexpression of tristetraprolin (TTP), but not its RNA binding mutant or the other ARE-binding proteins tested, decreased cellular LARP4 levels. RNA coimmunoprecipitation showed that TTP specifically associated with LARP4 mRNA in vivo. Consistent with this, mouse LARP4 accumulated to higher levels in TTP gene knockout (KO) cells than in control cells. Stimulation of WT cells with tumor necrosis factor alpha (TNF-α), which rapidly induces TTP, robustly decreased LARP4 with a coincident time course but had no such effect on LARP4B or La protein or on LARP4 in the TTP KO cells. The TNF-α-induced TTP pulse was followed by a transient decrease in LARP4 mRNA that was quickly followed by a subsequent transient decrease in LARP4 protein. Involvement of LARP4 as a target of TNF-α-TTP regulation provides a clue as to how its functional activity may be used in a physiologic pathway.

The La-Related Proteins, a Family with Connections to Cancer

The evolutionarily-conserved La-related protein (LARP) family currently comprises Genuine La, LARP1, LARP1b, LARP4, LARP4b, LARP6 and LARP7. Emerging evidence suggests each LARP has a distinct role in transcription and/or mRNA translation that is attributable to subtle sequence variations within their La modules and specific C-terminal domains. As emerging research uncovers the function of each LARP, it is evident that La, LARP1, LARP6, LARP7 and possibly LARP4a and 4b are dysregulated in cancer. Of these, LARP1 is the first to be demonstrated to drive oncogenesis. Here, we review the role of each LARP and the evidence linking it to malignancy. We discuss a future strategy of targeting members of this protein family as cancer therapy.

(1)H, (15)N and (13)C chemical shift assignments of the La motif and RRM1 from human LARP6

We report here the nearly complete (1)H, (15)N and (13)C resonance assignment of the La motif and RNA recognition motif 1 of human LARP6, an RNA binding protein involved in regulating collagen synthesis.

Study of microRNAs (miRNAs) that are predicted to target the autoantigens Ro/SSA and La/SSB in primary Sjögren's Syndrome

The elevated tissue expression of Ro/SSA and La/SSB autoantigens appears to be crucial for the generation and perpetuation of autoimmune humoral responses against these autoantigens in Sjögren's syndrome (SS). The mechanisms that govern their expression are not known. miRNAs, the post-transcriptional regulators of gene expression, might be implicated. We have identified previously the miRNAs let7b, miR16, miR181a, miR200b-3p, miR200b-5p, miR223 and miR483-5p that are predicted to target Ro/SSA [Ro52/tripartite motif-containing protein 21 (TRIM21), Ro60/TROVE domain family, member 2 (TROVE2)] and La/SSB mRNAs. To study possible associations with autoantigen mRNA expression and disease features, their expression was investigated in minor salivary gland (MSG) tissues, peripheral blood mononuclear cells (PBMC) and long-term cultured non-neoplastic salivary gland epithelial cells (SGEC) from 29 SS patients (20 of 29 positive for autoantibodies to Ro/SSA and La/SSB) and 24 sicca-complaining controls. The levels of miR16 were up-regulated in MSGs, miR200b-3p in SGECs and miR223 and miR483-5p in PBMCs of SS patients compared to sicca-complaining controls. The MSG levels of let7b, miR16, miR181a, miR223 and miR483-5p were correlated positively with Ro52/TRIM21-mRNA. miR181a and miR200b-3p were correlated negatively with Ro52/TRIM21 and Ro60/TROVE2 mRNAs in SGECs, respectively, whereas let7b, miR200b-5p and miR223 associated with La/SSB-mRNA. In PBMCs, let7b, miR16, miR181a and miR483-5p were correlated with Ro52/TRIM21, whereas let7b, miR16 and miR181a were also associated with La/SSB-mRNA expression. Significantly lower miR200b-5p levels were expressed in SS patients with mucosa-associated lymphoid tissue (MALT) lymphoma compared to those without. Our findings indicate that miR16, miR200b-3p, miR223 and miR483-5p are deregulated in SS, but the exact role of this deregulation in disease pathogenesis and autoantigen expression needs to be elucidated.

LARP1 post-transcriptionally regulates mTOR and contributes to cancer progression

RNA-binding proteins (RBPs) bind to and post-transcriptionally regulate the stability of mRNAs. La-related protein 1 (LARP1) is a conserved RBP that interacts with poly-A-binding protein and is known to regulate 5'-terminal oligopyrimidine tract (TOP) mRNA translation. Here, we show that LARP1 is complexed to 3000 mRNAs enriched for cancer pathways. A prominent member of the LARP1 interactome is mTOR whose mRNA transcript is stabilized by LARP1. At a functional level, we show that LARP1 promotes cell migration, invasion, anchorage-independent growth and in vivo tumorigenesis. Furthermore, we show that LARP1 expression is elevated in epithelial cancers such as cervical and non-small cell lung cancers, where its expression correlates with disease progression and adverse prognosis, respectively. We therefore conclude that, through the post-transcriptional regulation of genes such as mTOR within cancer pathways, LARP1 contributes to cancer progression.

The La-related protein 1-specific domain repurposes HEAT-like repeats to directly bind a 5'TOP sequence

La-related protein 1 (LARP1) regulates the stability of many mRNAs. These include 5'TOPs, mTOR-kinase responsive mRNAs with pyrimidine-rich 5' UTRs, which encode ribosomal proteins and translation factors. We determined that the highly conserved LARP1-specific C-terminal DM15 region of human LARP1 directly binds a 5'TOP sequence. The crystal structure of this DM15 region refined to 1.86 Å resolution has three structurally related and evolutionarily conserved helix-turn-helix modules within each monomer. These motifs resemble HEAT repeats, ubiquitous helical protein-binding structures, but their sequences are inconsistent with consensus sequences of known HEAT modules, suggesting this structure has been repurposed for RNA interactions. A putative mTORC1-recognition sequence sits within a flexible loop C-terminal to these repeats. We also present modelling of pyrimidine-rich single-stranded RNA onto the highly conserved surface of the DM15 region. These studies lay the foundation necessary for proceeding toward a structural mechanism by which LARP1 links mTOR signalling to ribosome biogenesis.

How hepatitis C virus modifies the immunological profile of Sjögren syndrome: analysis of 783 patients

INTRODUCTION

We conducted a study to analyze how infection by hepatitis C virus (HCV) may influence the immunological serum pattern of patients with Sjögren syndrome (SS).

METHODS

Since 1994, we have tested serum HCV-IgG antibodies in 783 patients with SS diagnosed according to the 1993 European classification criteria. The immunological profile at diagnosis was compared according to the presence or absence of HCV.

RESULTS

Of the 783 patients with SS, 105 (13.4 %) tested positive for HCV-IgG antibodies (88 females, 17 males, mean age at SS diagnosis: 62.9 years). Multivariate analysis showed that patients with SS-HCV had a higher mean age and a higher frequency of low C3/C4 levels, cryoglobulins, and hematological neoplasia compared with patients without HCV. The frequency of anti-La antibodies compared with anti-Ro antibodies was higher in patients with SS-HCV (17 % vs. 15 %) and lower in patients without HCV infection (30 % vs. 43 %). The frequency of concomitant detection of the three main cryoglobulin-related markers (cryoglobulins, rheumatoid factor activity, and C4 consumption) was threefold higher in patients with SS-HCV compared with patients without HCV. SS-HCV patients with genotype 1b showed the highest frequencies of immunological abnormalities related to cryoglobulins and the lowest frequencies of anti-Ro/La antibodies.

CONCLUSIONS

We found HCV infection in 13 % of a large series of Spanish patients with SS. The HCV-driven autoimmune response was characterized by a lower frequency of anti-Ro/La antibodies, an abnormal predominance of anti-La among anti-Ro antibodies, and a higher frequency of cryoglobulinemic-related immunological markers in comparison with patients without HCV infection. This immunological pattern may contribute to the poor outcomes found in patients with SS-HCV.

Endoplasmic reticulum stress causes autophagy and apoptosis leading to cellular redistribution of the autoantigens Ro/Sjögren's syndrome-related antigen A (SSA) and La/SSB in salivary gland epithelial cells

The aim of this study was to examine the levels of endoplasmic reticulum (ER) stress in minor salivary glands, to investigate the interplay between ER stress-induced autophagy and apoptosis in human salivary gland (HSG) cells and to test the effect of ER stress-induced apoptosis on the cellular redistribution of the two major Sjögren's syndrome (SS) autoantigens Ro/Sjögren's syndrome-related antigen A (SSA) and La/Sjögren's syndrome-related antigen B (SSB). Minor salivary gland biopsies from SS patients and sicca controls were examined by immunohistochemistry for the expression of 78 kDa glucose-regulated protein/binding immunoglobulin protein (GRP78/BiP) as an indicator of unfolded protein response (UPR). HSG cells were treated with thapsigargin (TG) and cell viability, autophagy and apoptosis were assessed. Immunoblot was applied to detect the conversion of LC3I to LC3II and the protein levels of GRP78/BiP and X-box binding protein-1 (XBP-1). Apoptosis was evaluated by a single-stranded DNA enzyme-linked immunosorbent assay (ELISA). Ro/SSA and La/SSB localization was visualized using immunofluorescence. GRP78/BiP was expressed by acinar and ductal epithelial cells in salivary glands of patients and sicca controls. TG treatment induced autophagy, as indicated by enhanced protein expression of LC3II. The protein levels of UPR marker XBP-1 were increased after TG treatment, while GRP78/BiP levels were decreased. TG treatment resulted in induction of HSG apoptosis. Ro/SSA and La/SSB autoantigens were localized predominantly to the cytoplasm in resting cells, while they were redistributed to cell membrane and blebs in the apoptotic cells. In conclusion, ER stress is activated in minor salivary gland epithelial cells from SS patients and controls. ER stress-induced apoptosis in HSG cells leads to cell surface and apoptotic blebs relocalization of Ro/SSA and La/SSB autoantigens.

MicroRNA-26a/b directly regulate La-related protein 1 and inhibit cancer cell invasion in prostate cancer

Our past studies of microRNA (miRNA) expression signatures of cancers including prostate cancer (PCa) revealed that microRNA-26a and microRNA-26b (miR-26a and miR-26b) were significantly downregulated in cancer tissues. In the present study, we found that restoration of miR-26a or miR-26b significantly inhibited PCa cell invasion. Gene expression data and in silico analysis showed that the gene encoding La-related protein 1 (LARP1) was a putative candidate of miR-26a and miR-26b regulation. Moreover, luciferase reporter assays revealed that LARP1 was a direct target of both miR-26a and miR-26b. Overexpression of LARP1 was observed in PCa clinical specimens and knockdown of LARP1 inhibited cancer cell migration. Therefore, LARP1 acted as an oncogene in PCa cells. Moreover, 'ribosome', 'RNA transport' and 'mTOR signaling pathway' were identified as LARP1-regulated pathways. Our present data suggested that loss of tumor-suppressive miR-26a and miR-26b enhanced cancer cell invasion in PCa through direct regulation of oncogenic LARP1. Elucidation of the molecular networks regulated by tumor-suppressive miRNAs will provide insights into the molecular mechanisms of PCa oncogenesis and metastasis.

Pleural Effusion In A Patient With Primary Sjögren's Syndrome Successfully Treated With Corticosteroids

Sjögren's syndrome is a systemic autoimmune disorder characterized by salivary insufficiency and lymphocytic infiltration of the exocrine glands. Bronchiolitis and bronchiectasis are common airway manifestations but interstitial pneumonitis, and lymphocytic interstitial pneumonitis may also occur. It rarely presents with pleuritis. We report a woman with primary Sjögren's syndrome who developed pleuritis with moderately large effusions and antibody levels for SS-A and SS-B in the serum without evidence of infection, malignancy or other collagen diseases. After the initial treatment, daily administration of 20 mg of oral prednisone has effectively controlled the serious manifestations of the disease with minimal side effects.