Latexin regulates the abundance of multiple cellular proteins in hematopoietic stem cells

The Intersection between Oral Microbiota, Host Gene Methylation and Patient Outcomes in Head and Neck Squamous Cell Carcinoma

Simple Summary

Recently, there has been increased recognition of an association between the bacterial microbiome and cancer. In this study, we characterized the non-HPV head and neck squamous cell carcinoma (HNSCC) microbiome. We found a significant enrichment of Fusobacterium, depletion of Streptococcus, and the microbial signatures of twelve bacterial genera distinguishing HNSCC. With increased Fusobacterium—in particular, F. nucleatum—in our HNSCC cohort and its known association with prognosis in colorectal cancers (CRC), we sought to further characterize the association between clinical outcomes and F. nucleatum, and the host interaction with F. nucleatum. We identified a higher abundance of F. nucleatum in non-smokers and an improved survival, in contrast to CRC. An integrative analysis also identified that the enrichment of F. nucleatum was associated with host gene promoter methylation, suggesting that the bacterial mircobiome status may have a potential role as a prognostic biomarker and be involved in the pathogenesis of HNSCC.

Abstract

The role of oral microbiota in head and neck squamous cell carcinoma (HNSCC) is poorly understood. Here we sought to evaluate the association of the bacterial microbiome with host gene methylation and patient outcomes, and to explore its potential as a biomarker for early detection or intervention. Here we performed 16S rRNA gene amplicon sequencing in sixty-eight HNSCC patients across both tissue and oral rinse samples to identify oral bacteria with differential abundance between HNSCC and controls. A subset of thirty-one pairs of HNSCC tumor tissues and the adjacent normal tissues were characterized for host gene methylation profile using bisulfite capture sequencing. We observed significant enrichments of Fusobacterium and Peptostreptococcus in HNSCC tumor tissues when compared to the adjacent normal tissues, and in HNSCC oral rinses when compared to healthy subjects, while ten other bacterial genera were largely depleted. These HNSCC-related bacteria were discriminative for HNSCC and controls with area under the receiver operating curves (AUCs) of 0.84 and 0.86 in tissue and oral rinse samples, respectively. Moreover, Fusobacterium nucleatum abundance in HNSCC cases was strongly associated with non-smokers, lower tumor stage, lower rate of recurrence, and improved disease-specific survival. An integrative analysis identified that enrichment of F. nucleatum was associated with host gene promoter methylation, including hypermethylation of tumor suppressor genes LXN and SMARCA2, for which gene expressions were downregulated in the HNSCC cohort from The Cancer Genome Atlas. In conclusion, we identified a taxonomically defined microbial consortium associated with HNSCC that may have clinical potential regarding biomarkers for early detection or intervention. Host–microbe interactions between F. nucleatum enrichment and clinical outcomes or host gene methylation imply a potential role of F. nucleatum as a pro-inflammatory driver in initiating HNSCC without traditional risk factors, which warrants further investigation for the underlying mechanisms.

Latexin regulation by HMGB2 is required for hematopoietic stem cell maintenance

Hematopoietic stem cells provide life-long production of blood cells and undergo self-renewal division in order to sustain the stem cell pool. Homeostatic maintenance of hematopoietic stem cell pool and blood cell production is vital for the organism to survive. We previously reported that latexin is a negative regulator of hematopoietic stem cells in mice. Its natural variation in the expression is inversely correlated with hematopoietic stem cell number. However, the molecular mechanisms regulating latexin transcription remain largely unknown, and the genetic factors contributing to its natural variation are not clearly defined. Here we discovered a chromatin protein, high-mobility group protein B2, as a novel transcriptional suppressor of latexin by using DNA pull-down and mass spectrometry. High-mobility group protein B2 knockdown increases latexin expression at transcript and protein levels, and decreases hematopoietic stem cell number and regeneration capacity in vivo. Concomitant blockage of latexin activation significantly reverses these phenotypic changes, suggesting that latexin is one of the downstream targets and functional mediators of high-mobility group protein B2. We further identified a functional single nucleotide polymorphism, rs31528793, in the latexin promoter that binds to high-mobility group protein B2 and affects the promoter activity. G allelic variation in rs31528793 associates with the higher latexin expression and lower hematopoietic stem cell number, whereas C allele indicates the lower latexin expression and higher stem cell number. This study reveals for the first time that latexin transcription is regulated by both transacting (high-mobility group protein B2) and cis-acting (single nucleotide polymorphism rs31528793) factors. It uncovers the functional role of naturally occurring genetic variants, in combination with epigenetic regulator, in determining differential gene expression and phenotypic diversity in the hematopoietic stem cell population.

The putative tumour suppressor protein Latexin is secreted by prostate luminal cells and is downregulated in malignancy

Loss of latexin (LXN) expression negatively correlates with the prognosis of several human cancers. Despite association with numerous processes including haematopoietic stem cell (HSC) fate, inflammation and tumour suppression, a clearly defined biological role for LXN is still lacking. Therefore, we sought to understand LXN expression and function in the normal and malignant prostate to assess its potential as a therapeutic target. Our data demonstrate that LXN is highly expressed in normal prostate luminal cells but downregulated in high Gleason grade cancers. LXN protein is both cytosolic and secreted by prostate cells and expression is directly and potently upregulated by all-trans retinoic acid (atRA). Whilst overexpression of LXN in prostate epithelial basal cells did not affect cell fate, LXN overexpression in the luminal cancer line LNCaP reduced plating efficiency. Transcriptome analysis revealed that LXN overexpression had no direct effects on gene expression but had significant indirect effects on important genes involved in both retinoid metabolism and IFN-associated inflammatory responses. These data highlight a potential role for LXN in retinoid signaling and inflammatory pathways. Investigating the effects of LXN on immune cell function in the tumour microenvironment (TME) may reveal how observed intratumoural loss of LXN affects the prognosis of many adenocarcinomas.

Tumor suppressor RARRES1 links tubulin deglutamylation to mitochondrial metabolism and cell survival

RARRES1, a retinoic acid regulated carboxypeptidase inhibitor associated with fatty acid metabolism, stem cell differentiation and tumorigenesis is among the most commonly methylated loci in multiple cancers but has no known mechanism of action. Here we show that RARRES1 interaction with cytoplasmic carboxypeptidase 2 (CCP2) inhibits tubulin deglutamylation, which in turn regulates the mitochondrial voltage dependent anion channel (VDAC1), mitochondrial membrane potential, AMPK activation, energy balance and metabolically reprograms cells and zebrafish to a more energetic and anabolic phenotype. Depletion of RARRES1 also increases expression of stem cell markers, promotes anoikis, anchorage independent growth and insensitivity to multiple apoptotic stimuli. As depletion of CCP2 or inhibition of VDAC1 reverses the effects of RARRES1 depletion on energy balance and cell survival we conclude that RARRES1 modulation of CCP2-modulated tubulin-mitochondrial VDAC1 interactions is a fundamental regulator of cancer and stem cell metabolism and survival.

Latexin and hematopoiesis

PURPOSE OF REVIEW

Hematopoietic stem cells (HSCs) produce mature blood cells throughout lifetime. Natural genetic diversity offers an important yet largely untapped reservoir for deciphering regulatory mechanisms of HSCs and hematopoiesis. In this review, we explore the role of latexin, identified by natural variation, in regulating homeostatic and stress hematopoiesis, unravel the underlying signaling pathways, and propose its therapeutic implication.

RECENT FINDINGS

Latexin acts endogenously in HSCs to negatively regulate their population size by enhancing apoptosis and by decreasing self-renewal. Deletion of latexin in vivo increases HSC repopulation capacity and survival, expands the entire hematopoietic system, and mitigates myelosuppression. Latexin inactivation downregulates thrombospondin 1 (Thbs1). It inhibits nuclear translocation of ribosomal protein subunit 3 (Rps3), a novel latexin-binding protein, and sensitizes hematopoietic cells to radiation-induced cell death. However, how latexin-Rps3 pathway regulates Thbs1 transcription is unclear. Latexin is downregulated in cancer cells because of promoter hypermethylation, but latexin-depleted mice do not inherently develop hematologic malignancies even with aging. The mechanism of action of latexin in tumorigenesis remains largely unknown.

SUMMARY

Understanding how latexin regulates HSC survival, self-renewal, and stress response will advance our knowledge of HSC biology. It will facilitate the development of a novel therapeutic strategy for hematopoietic regeneration and cancer treatment.

Lysine-specific demethylase 1 inhibitors prevent teratoma development from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are creating great expectations for regenerative medicine. However, safety strategies must be put in place to guard against teratoma formation after transplantation of hiPSC-derived cells into patients. Recent studies indicate that epigenetic regulators act at the initial step of tumorigenesis. Using gain-of-function and loss-of-function approaches, we show here that the expression and function of lysine-specific demethylase 1 (LSD1) are tightly regulated in hiPSCs, and their deregulation underlies the development of teratomas. Consistent with these results, we demonstrate that an LSD1 inhibitor, S2157, prevented teratoma formation from hiPSCs transplanted into immunodeficient mice. This novel action of LSD1 and the effects of its inhibition potentially allow for the development of new clinical applications and therapeutic strategies using hiPSCs.

Latexin Inactivation Enhances Survival and Long-Term Engraftment of Hematopoietic Stem Cells and Expands the Entire Hematopoietic System in Mice

Natural genetic diversity offers an important yet largely untapped resource to decipher the molecular mechanisms regulating hematopoietic stem cell (HSC) function. Latexin (Lxn) is a negative stem cell regulatory gene identified on the basis of genetic diversity. By using an Lxn knockout mouse model, we found that Lxn inactivation in vivo led to the physiological expansion of the entire hematopoietic hierarchy. Loss of Lxn enhanced the competitive repopulation capacity and survival of HSCs in a cell-intrinsic manner. Gene profiling of Lxn-null HSCs showed altered expression of genes enriched in cell-matrix and cell-cell interactions. Thrombospondin 1 (Thbs1) was a potential downstream target with a dramatic downregulation in Lxn-null HSCs. Enforced expression of Thbs1 restored the Lxn inactivation-mediated HSC phenotypes. This study reveals that Lxn plays an important role in the maintenance of homeostatic hematopoiesis, and it may lead to development of safe and effective approaches to manipulate HSCs for clinical benefit.

Bone Microenvironment Changes in Latexin Expression Promote Chemoresistance

Although docetaxel is the standard of care for advanced prostate cancer, most patients develop resistance to docetaxel. Therefore, elucidating the mechanism that underlies resistance to docetaxel is critical to enhance therapeutic intervention. Mining cDNA microarray from the PC-3 prostate cancer cell line and its docetaxel-resistant derivative (PC3-TxR) revealed decreased latexin (LXN) expression in the resistant cells. LXN expression was inversely correlated with taxane resistance in a panel of prostate cancer cell lines. LXN knockdown conferred docetaxel resistance to prostate cancer cells in vitro and in vivo, whereas LXN overexpression reduced docetaxel resistance in several prostate cancer cell lines. A mouse model of prostate cancer demonstrated that prostate cancer cells developed resistance to docetaxel in the bone microenvironment, but not the soft tissue microenvironment. This was associated with decreased LXN expression in prostate cancer cells in the bone microenvironment compared with the soft tissue microenvironment. It was identified that bone stromal cells decreased LXN expression through methylation and induced chemoresistance in prostate cancer in vitro These findings reveal that a subset of prostate cancer develops docetaxel resistance through loss of LXN expression associated with methylation and that the bone microenvironment promotes this drug resistance phenotype.Implications: This study suggests that the LXN pathway should be further explored as a viable target for preventing or reversing taxane resistance in prostate cancer. Mol Cancer Res; 15(4); 457-66. ©2017 AACR.

Quantitative trait gene Slit2 positively regulates murine hematopoietic stem cell numbers

Hematopoietic stem cells (HSC) demonstrate natural variation in number and function. The genetic factors responsible for the variations (or quantitative traits) are largely unknown. We previously identified a gene whose differential expression underlies the natural variation of HSC numbers in C57BL/6 (B6) and DBA/2 (D2) mice. We now report the finding of another gene, Slit2, on chromosome 5 that also accounts for variation in HSC number. In reciprocal chromosome 5 congenic mice, introgressed D2 alleles increased HSC numbers, whereas B6 alleles had the opposite effect. Using gene array and quantitative polymerase chain reaction, we identified Slit2 as a quantitative trait gene whose expression was positively correlated with the number of HSCs. Ectopic expression of Slit2 not only increased the number of the long-term colony forming HSCs, but also enhanced their repopulation capacity upon transplantation. Therefore, Slit2 is a novel quantitative trait gene and a positive regulator of the number and function of murine HSCs. This finding suggests that Slit2 may be a potential therapeutic target for the effective in vitro and in vivo expansion of HSCs without compromising normal hematopoiesis.

Latexin exhibits tumor-suppressor potential in pancreatic ductal adenocarcinoma

Recent studies suggest that latexin (Lxn) expression is involved in stem cell regulation and that it plays significant roles in tumor cell migration and invasion. The clinicopathological significance of Lxn expression and its possible correlation with CD133 expression in pancreatic ductal adenocarcinoma (PDAC) is currently unknown. In the present study, immunohistochemical analysis was performed to determine Lxn and CD133 expression in 43 PDAC patient samples and in 32 corresponding adjacent non-cancerous samples. The results were analyzed and compared with patient age, gender, tumor site and size, histological grade, clinical stage and overall mean survival time. Lxn expression was clearly decreased in the PDAC tissues compared with that in the adjacent non-cancerous tissues, while CD133 expression was increased. Low Lxn expression in the PDAC tissues was significantly correlated with tumor size (P=0.002), histological grade (P=0.000), metastasis (P=0.007) and clinical stage (P=0.018), but not with age (P=0.451), gender (P=0.395) or tumor site (P=0.697). Kaplan-Meier survival analysis revealed that low Lxn expression was significantly correlated with reduced overall survival time (P=0.000). Furthermore, Lxn expression was found to be inversely correlated with CD133 expression (r=−0.485, P=0.001). Furthermore, CD133-positive MIA PaCa-2 pancreatic tumor cells were sorted by magnetic-activated cell sorting (MACS), and those that overexpressed Lxn exhibited a significantly higher rate of apoptosis and lower proliferative activity. Our findings suggest that Lxn may function as a tumor suppressor that targets CD133-positive pancreatic cancer cells.

Analysis of dermal papilla cell interactome using STRING database to profile the ex vivo hair growth inhibition effect of a vinca alkaloid drug, colchicine

Dermal papillae (DPs) control the formation of hair shafts. In clinical settings, colchicine (CLC) induces patients' hair shedding. Compared to the control, the ex vivo hair fiber elongation of organ cultured vibrissa hair follicles (HFs) declined significantly after seven days of CLC treatment. The cultured DP cells (DPCs) were used as the experimental model to study the influence of CLC on the protein dynamics of DPs. CLC could alter the morphology and down-regulate the expression of alkaline phosphatase (ALP), the marker of DPC activity, and induce IκBα phosphorylation of DPCs. The proteomic results showed that CLC modulated the expression patterns (fold>2) of 24 identified proteins, seven down-regulated and 17 up-regulated. Most of these proteins were presumably associated with protein turnover, metabolism, structure and signal transduction. Protein-protein interactions (PPI) among these proteins, established by Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) database, revealed that they participate in protein metabolic process, translation, and energy production. Furthermore, ubiquitin C (UbC) was predicted to be the controlling hub, suggesting the involvement of ubiquitin-proteasome system in modulating the pathogenic effect of CLC on DPC.

Molecular mechanism of cell death induced by king cobra (Ophiophagus hannah) venom l-amino acid oxidase

Snake venom LAAOs have been reported to exhibit a wide range of pharmacological activities, including cytotoxic, edema-inducing, platelet aggregation-inducing/platelet aggregation-inhibiting, bactericidal and antiviral activities. A heat-stable form of l-amino acid oxidase isolated from king cobra (Ophiophagus hannah) venom (OH-LAAO) has been shown to exhibit very potent cytotoxicity against human tumorigenic cells but not in their non-tumorigenic counterparts, and the cytotoxicity was due to the apoptosis-inducing effect of the enzyme. In this work, the molecular mechanism of cell death induced by OH-LAAO was investigated. The enzyme exerts its apoptosis-inducing effect presumably via both intrinsic and extrinsic pathways as suggested by the increase in caspase-8 and -9 activities. Oligonucleotide microarray analysis showed that the expression of a total of 178 genes was significantly altered as a result of oxidative stress induced by the hydrogen peroxide generated by the enzyme. Of the 178 genes, at least 27 genes are involved in apoptosis and cell death. These alterations of gene expression was presumably caused by the direct cytotoxic effect of H2O2 generated during the enzymatic reaction, as well as the non-specific oxidative modifications of signaling molecules that eventually lead to apoptosis and cell death. The very substantial up-regulation of cytochrome P450 genes may also contribute to the potent cytotoxic action of OH-LAAO by producing excessive reactive oxygen species (ROS). In conclusion, the potent apoptosis inducing activity of OH-LAAO was likely due to the direct cytotoxic effect of H2O2 generated during the enzymatic reaction, as well as the non-specific oxidation of signalling molecules.

Latexin sensitizes leukemogenic cells to gamma-irradiation-induced cell-cycle arrest and cell death through Rps3 pathway

Leukemia is a leading cause of cancer death. Recently, the latexin (Lxn) gene was identified as a potential tumor suppressor in several types of solid tumors and lymphoma, and Lxn expression was found to be absent or downregulated in leukemic cells. Whether Lxn functions as a tumor suppressor in leukemia and what molecular and cellular mechanisms are involved are unknown. In this study, the myeloid leukemogenic FDC-P1 cell line was used as a model system and Lxn was ectopically expressed in these cells. Using the protein pull-down assay and mass spectrometry, ribosomal protein subunit 3 (Rps3) was identified as a novel Lxn binding protein. Ectopic expression of Lxn inhibited FDC-P1 growth in vitro. More surprisingly, Lxn enhanced gamma irradiation-induced DNA damages and induced cell-cycle arrest and massive necrosis, leading to depletion of FDC-P1 cells. Mechanistically, Lxn inhibited the nuclear translocation of Rps3 upon radiation, resulting in abnormal mitotic spindle formation and chromosome instability. Rps3 knockdown increased the radiation sensitivity of FDC-P1, confirming that the mechanism of action of Lxn is mediated by Rps3 pathway. Moreover, Lxn enhanced the cytotoxicity of chemotherapeutic agent, VP-16, on FDC-P1 cells. Our study suggests that Lxn itself not only suppresses leukemic cell growth but also potentiates the cytotoxic effect of radio- and chemotherapy on cancer cells. Lxn could be a novel molecular target that improves the efficacy of anti-cancer therapy.

Latexin exhibits tumor suppressor potential in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary cancer of the liver and latexin is downregulated in several types of human cancer. However, latexin expression in HCC remains unknown. mRNA expression of latexin in HCC samples and HCC-derived cell lines was detected by semi‑quantitative PCR and real-time PCR, while protein expression was assessed by immunohistochemistry. The role of latexin in the regulation of the proliferation of HCC-derived cells was investigated both in vitro and in vivo. Flow cytometry was used to differentiate cell cycle distribution in SK-hep-1 and YY-8103. In a total of 60 paired HCC specimens, compared with adjacent non-cancer tissues, latexin mRNA was downregulated in 42 specimens. Immunohistochemical analysis showed a significant reduction in latexin expression in HCC compared to control tissues. Overexpression of latexin inhibited SK-hep-1 and HepG2 cellular colony formation and tumor growth. Conversely, YY‑8103 and Focus cells transfected with shRNA enhanced colony formation and tumor growth. Latexin overexpression promoted cell cycle arrest in the G0/G1 phase in SK-hep-1 and silencing of latexin promoted the cell cycle transition from G0/G1 phase to S phase in YY-8103. The cyclin-dependent kinase inhibitors (CDKIs) (p21Cip1, p27Kip1, p15INK4B), cyclin D1 and cyclin E were shown to be differentially expressed in latexin-overexpressed cells and latexin-silenced cells. These results indicated that latexin may be an effective target for gene therapy.

Longitudinal transcriptomic dysregulation in the peripheral blood of transgenic Huntington's disease monkeys

Background

Huntington’s Disease (HD) is a progressive neurodegenerative disorder caused by an expansion in the polyglutamine (polyQ) region of the Huntingtin (HTT) gene. The clinical features of HD are characterized by cognitive, psychological, and motor deficits. Molecular instability, a core component in neurological disease progression, can be comprehensively evaluated through longitudinal transcriptomic profiling. Development of animal models amenable to longitudinal examination enables distinct disease-associated mechanisms to be identified.

Results

Here we report the first longitudinal study of transgenic monkeys with genomic integration of various lengths of the human HTT gene and a range of polyQ repeats. With this unique group of transgenic HD nonhuman primates (HD monkeys), we profiled over 47,000 transcripts from peripheral blood collected over a 2 year timespan from HD monkeys and age-matched wild-type control monkeys.

Conclusions

Messenger RNAs with expression patterns which diverged with disease progression in the HD monkeys considerably facilitated our search for transcripts with diagnostic or therapeutic potential in the blood of human HD patients, opening up a new avenue for clinical investigation.

Retinoic acid represses invasion and stem cell phenotype by induction of the metastasis suppressors RARRES1 and LXN

The mouse haematopoietic stem cell (SC) regulator Latexin (LXN) is the only known homologue of the retinoic acid receptor responder 1 (RARRES1) gene. Both genes lie adjacent on chromosome 3 and differ mostly by the presence of a transmembrane domain in RARRES1. Despite their homology, it is not known whether they possess similar regulatory mechanisms, cellular localization and function. Here, we identified RARRES1 and LXN as highly significantly downregulated genes in human prostate SCs, whose expression was induced by the pro-differentiation agent all-trans retinoic acid (atRA). AtRA induced expression in the most differentiated cells compared with the SC fraction, suggesting that this subpopulation was less responsive to atRA. Small interfering RNA suppression of RARRES1 and LXN enhanced the SC properties of primary prostate cultures, as shown by a significant increase in their colony-forming ability. Expression of both RARRES1 and LXN was co-ordinately repressed by DNA methylation in prostate cancer cell lines and inhibition of RARRES1 and LXN increased the invasive capacity of primary prostate cultures, which also fully rescued an inhibitory effect induced by atRA. Moreover, we showed that RARRES1 and LXN reside within different sub-cellular compartments, providing evidence that RARRES1 is not a plasma membrane protein as previously supposed but is located primarily in the endoplasmic reticulum; whereas LXN was detected in the nucleus of prostate epithelial cells. Thus, LXN and RARRES1 are potential tumour suppressor genes, which are co-ordinately regulated, SC-silenced genes functioning to suppress invasion and colony-forming ability of prostate cancer cells; yet the proteins reside within different sub-cellular compartments.

Homopiperazine derivatives as a novel class of proteasome inhibitors with a unique mode of proteasome binding

The proteasome is a proteolytic machinery that executes the degradation of polyubiquitinated proteins to maintain cellular homeostasis. Proteasome inhibition is a unique and effective way to kill cancer cells because they are sensitive to proteotoxic stress. Indeed, the proteasome inhibitor bortezomib is now indispensable for the treatment of multiple myeloma and other intractable malignancies, but is associated with patient inconvenience due to intravenous injection and emerging drug resistance. To resolve these problems, we attempted to develop orally bioavailable proteasome inhibitors with distinct mechanisms of action and identified homopiperazine derivatives (HPDs) as promising candidates. Biochemical and crystallographic studies revealed that some HPDs inhibit all three catalytic subunits (ß 1, ß 2 and ß 5) of the proteasome by direct binding, whereas bortezomib and other proteasome inhibitors mainly act on the ß5 subunit. Proteasome-inhibitory HPDs exhibited cytotoxic effects on cell lines from various hematological malignancies including myeloma. Furthermore, K-7174, one of the HPDs, was able to inhibit the growth of bortezomib-resistant myeloma cells carrying a ß5-subunit mutation. Finally, K-7174 had additive effects with bortezomib on proteasome inhibition and apoptosis induction in myeloma cells. Taken together, HPDs could be a new class of proteasome inhibitors, which compensate for the weak points of conventional ones and overcome the resistance to bortezomib.