A human leucyl-tRNA synthetase as an anticancer target

Dickkopf 4 Alone and in Combination with Leucyl-tRNA Synthetase as a Good Prognostic Biomarker for Human Colorectal Cancer

The prognosis of patients with colorectal cancer (CRC) is affected by invasion and metastasis. Leucyl-tRNA synthetase (LARS) was shown to be related to the growth and migration of lung cancer cells. Dickkopf 4 (DKK4) is known as a Wnt/β-catenin pathway inhibitor, and its upregulation was reported in several cancers. However, the clinical significance of LARS and DKK4 in human CRC has not been clearly defined. We investigated the expression of LARS and DKK4 by immunohistochemical staining in tissue microarrays from 642 primary CRC patients and analyzed the relationship between their expression and the clinicopathological characteristics of CRC patients. LARS and DKK4 expressions were not related to gender, age at surgery, histologic grade, size, tumor location, tumor invasion, or metastasis, but LARS expression was significantly correlated with TNM stage, N stage, and lymph node metastasis. DKK4 expression was inversely related to the TNM stage and N stage. Survival analysis demonstrated that the OS and DFS in the LARS high expression group were not different compared to the LARS low expression group. OS and DFS in the DKK4 high expression group were significantly higher than in the DKK4 low expression group. In addition, OS and DFS in the group with the combination of the LARS high/DKK4 low expression were significantly lower than in the LARS high/DKK4 high expression group. The low expression of DKK4 alone can be used as a predictor of relapse in CRC patients. In addition, DKK4 low expression in the case of LARS high expression can be used as a poor prognostic factor in CRC patients. Thus, our findings suggest that DKK4 alone or in combination with LARS at diagnosis may be a useful prognostic factor for CRC.

tRNA Function and Dysregulation in Cancer

Transfer RNA (tRNA) is a central component of protein synthesis and plays important roles in epigenetic regulation of gene expression in tumors. tRNAs are also involved in many cell processes including cell proliferation, cell signaling pathways and stress response, implicating a role in tumorigenesis and cancer progression. The complex role of tRNA in cell regulation implies that an understanding of tRNA function and dysregulation can be used to develop treatments for many cancers including breast cancer, colon cancer, and glioblastoma. Moreover, tRNA modifications including methylation are necessary for tRNA folding, stability, and function. In response to certain stress conditions, tRNAs can be cleaved in half to form tiRNAs, or even shorter tRNA fragments (tRF). tRNA structure and modifications, tiRNA induction of stress granule formation, and tRF regulation of gene expression through the repression of translation can all impact a cell’s fate. This review focuses on how these functions of tRNAs, tiRNA, and tRFs can lead to tumor development and progression. Further studies focusing on the specific pathways of tRNA regulation could help identify tRNA biomarkers and therapeutic targets, which might prevent and treat cancers.

LARS2 Regulates Apoptosis via ROS-Mediated Mitochondrial Dysfunction and Endoplasmic Reticulum Stress in Ovarian Granulosa Cells

Several studies have indicated that mutations of LARS2 are associated with premature ovarian insufficiency (POI). However, the pathogenic mechanism of LARS2 in POI has not been reported yet. In the present study, the expression levels of LARS2 and E2F1 in granulosa cells (GCs) of POI patients were examined. CCK-8 and Edu assay were performed to determine the effect of LARS2 on cell proliferation. Apoptosis rate, mitochondrial membrane potential, reactive oxygen species (ROS), and cytoplasm Ca²⁺ levels were analyzed by flow cytometry. Western blot was conducted to evaluate the expression level of genes affected by LARS2. Transmission electron microscopy (TEM) was used to observe mitochondrial structure in GCs. Chromatin immunoprecipitation (ChIP) was used to evaluate the regulatory effect of E2F1 on Mfn-2 expression. Our results showed that LARS2 expression was downregulated in GCs of POI patients. Silencing of LARS2 inhibited cell proliferation and promoted the apoptosis of GCs. Meanwhile, LARS2 knockdown could induce mitochondrial dysfunction and accumulation of ROS levels. Moreover, ROS was found to be involved in the antiproliferation, proapoptotic, and endoplasmic reticulum (ER) stress effects of LARS2 knockdown. Furthermore, we also found that the expression level of E2F1 was positively correlated with LARS2. In addition, E2F1 could bind at the -61/-46 region of Mfn-2 promoter and regulated MFN-2 transcription. These findings demonstrated that LARS2 could promote the expression of E2F1. E2F1 mediated the effect of LARS2 on Mfn-2 expression via targeting the promoter region of Mfn-2, in which subsequently regulated cell proliferation and apoptosis, which resulted in the etiology of POI. This study will provide useful information for further investigations on the LARS2 in the occurrence of POI.

Genome-wide analysis of therapeutic response uncovers molecular pathways governing tamoxifen resistance in ER+ breast cancer

Background

Prioritization of breast cancer patients based on the risk of resistance to tamoxifen plays a significant role in personalized therapeutic planning and improving disease course and outcomes.

Methods

In this work, we demonstrate that a genome-wide pathway-centric computational framework elucidates molecular pathways as markers of tamoxifen resistance in ER+ breast cancer patients. In particular, we associated activity levels of molecular pathways with a wide spectrum of response to tamoxifen, which defined markers of tamoxifen resistance in patients with ER+ breast cancer.

Findings

We identified five biological pathways as markers of tamoxifen failure and demonstrated their ability to predict the risk of tamoxifen resistance in two independent patient cohorts (Test cohort1: log-rank p-value = 0.02, adjusted HR = 3.11; Test cohort2: log-rank p-value = 0.01, adjusted HR = 4.24). We have shown that these pathways are not markers of aggressiveness and outperform known markers of tamoxifen response. Furthermore, for adoption into clinic, we derived a list of pathway read-out genes and their associated scoring system, which assigns a risk of tamoxifen resistance for new incoming patients.

Interpretation

We propose that the identified pathways and their read-out genes can be utilized to prioritize patients who would benefit from tamoxifen treatment and patients at risk of tamoxifen resistance that should be offered alternative regimens.

Funding

This work was supported by the Rutgers SHP Dean's research grant, Rutgers start-up funds, Libyan Ministry of Higher Education and Scientific Research, and Katrina Kehlet Graduate Award from The NJ Chapter of the Healthcare Information Management Systems Society.

Therapeutic effects of the novel Leucyl-tRNA synthetase inhibitor BC-LI-0186 in non-small cell lung cancer

Objective:

Leucyl-tRNA synthetase (LRS) is an aminoacyl-tRNA synthetase catalyzing ligation of leucine to its cognate tRNA and is involved in the activation of mTORC1 by sensing cytoplasmic leucine. In this study, the usefulness of LRS as a therapeutic target of non-small cell lung cancer (NSCLC) and the anticancer effect of the LRS inhibitor, BC-LI-0186, was evaluated.

Methods:

LRS expression and the antitumor effect of BC-LI-0186 were evaluated by immunohistochemical staining, immunoblotting, and live cell imaging. The in vivo antitumor effect of BC-LI-0186 was evaluated using Lox-Stop-Lox (LSL) K-ras G12D mice.

Results:

LRS was frequently overexpressed in NSCLC tissues, and its expression was positively correlated with mTORC1 activity. The guanosine-5’-triphosphate (GTP) binding status of RagB was related to the expression of LRS and the S6K phosphorylation. siRNA against LRS inhibited leucine-mediated mTORC1 activation and cell growth. BC-LI-0186 selectively inhibited phosphorylation of S6K without affecting phosphorylation of AKT and leucine-mediated co-localization of Raptor and LAMP2 in the lysosome. BC-LI-0186 induced cleaved poly (ADP-ribose) polymerase (PARP) and caspase-3 and increase of p62 expression, showing that it has the autophagy-inducing property. BC-LI-0186 has the cytotoxic effect at nanomolar concentration and its GI₅₀ value was negatively correlated with the degree of LRS expression. BC-LI-0186 showed the antitumor effect, which was comparable with that of cisplatin, and mTORC1 inhibitory effect in a lung cancer model.

Conclusions:

BC-LI-0186 inhibits the noncanonical mTORC1-activating function of LRS. These results provide a new therapeutic strategy for NSCLC and warrant future clinical development by targeting LRS.

Discovering simple phenylboronic acid and benzoxaborole derivatives for experimental oncology - phase cycle-specific inducers of apoptosis in A2780 ovarian cancer cells

Objective The aim of the study was to evaluate the antiproliferative potential of simple phenylboronic acid and benzoxaborole derivatives as well as to provide preliminary insight into their mode of action in cancer cells in vitro. Methods The antiproliferative activity was assessed in five diverse cancer cell lines via the SRB method (sulforhodamine B) or MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method after 72 h of treatment. Further studies of the mechanism of action consisted of the influence of the compounds on cell cycle progression and apoptosis induction, which was assessed by flow cytometry, caspase-3 enzymatic activity, fluorescence microscopy and western blot analysis. Results A clear structure-activity relationship was observed for both groups of compounds with several representatives evaluated as highly active antiproliferative agents with low micromolar [Formula: see text] values. 2-Fluoro-6-formylphenylboronic acid (18) and 3-morpholino-5-fluorobenzoxaborole (27) exhibited strong cell cycle arrest induction in G₂/M associated with caspase-3 activation in an A2780 ovarian cancer cell line. These events were accompanied by a mitotic catastrophe cell morphology and an increased percentage of aneuploid and tetraploid cells. Further experiments indicated that the compounds were phase cycle-specific agents since cells co-treated with hydroxyurea were less sensitive. The observed cell cycle arrest resulted from significant p21 accumulation and was associated neither with cyclin B1 nor β-tubulin degradation. Conclusion Phenylboronic acid and benzoxaborole derivatives were found to be highly promising antiproliferative and proapoptotic compounds with a cell cycle-specific mode of action. The presented data support their candidacy for further studies as a novel class of potential anticancer agents.

Correlation of histopathologic characteristics to protein expression and function in malignant melanoma

Background

Metastatic melanoma is still one of the most prevalent skin cancers, which upon progression has neither a prognostic marker nor a specific and lasting treatment. Proteomic analysis is a versatile approach with high throughput data and results that can be used for characterizing tissue samples. However, such analysis is hampered by the complexity of the disease, heterogeneity of patients, tumors, and samples themselves. With the long term aim of quest for better diagnostics biomarkers, as well as predictive and prognostic markers, we focused on relating high resolution proteomics data to careful histopathological evaluation of the tumor samples and patient survival information.

Patients and methods

Regional lymph node metastases obtained from ten patients with metastatic melanoma (stage III) were analyzed by histopathology and proteomics using mass spectrometry. Out of the ten patients, six had clinical follow-up data. The protein deep mining mass spectrometry data was related to the histopathology tumor tissue sections adjacent to the area used for deep-mining. Clinical follow-up data provided information on disease progression which could be linked to protein expression aiming to identify tissue-based specific protein markers for metastatic melanoma and prognostic factors for prediction of progression of stage III disease.

Results

In this feasibility study, several proteins were identified that positively correlated to tumor tissue content including IF6, ARF4, MUC18, UBC12, CSPG4, PCNA, PMEL and MAGD2. The study also identified MYC, HNF4A and TGFB1 as top upstream regulators correlating to tumor tissue content. Other proteins were inversely correlated to tumor tissue content, the most significant being; TENX, EHD2, ZA2G, AOC3, FETUA and THRB. A number of proteins were significantly related to clinical outcome, among these, HEXB, PKM and GPNMB stood out, as hallmarks of processes involved in progression from stage III to stage IV disease and poor survival.

Conclusion

In this feasibility study, promising results show the feasibility of relating proteomics to histopathology and clinical outcome, and insight thus can be gained into the molecular processes driving the disease. The combined analysis of histological features including the sample cellular composition with protein expression of each metastasis enabled the identification of novel, differentially expressed proteins. Further studies are necessary to determine whether these putative biomarkers can be utilized in diagnostics and prognostic prediction of metastatic melanoma.