Association of Aurora A and gamma-tubulin expression in astrocytomas and patient survival

Dysregulation of Microtubule Nucleating Proteins in Cancer Cells

Simple Summary

The dysfunction of microtubule nucleation in cancer cells changes the overall cytoskeleton organization and cellular physiology. This review focuses on the dysregulation of the γ-tubulin ring complex (γ-TuRC) proteins that are essential for microtubule nucleation. Recent research on the high-resolution structure of γ-TuRC has brought new insight into the microtubule nucleation mechanism. We discuss the effect of γ-TuRC protein overexpression on cancer cell behavior and new drugs directed to γ-tubulin that may offer a viable alternative to microtubule-targeting agents currently used in cancer chemotherapy.

Abstract

In cells, microtubules typically nucleate from microtubule organizing centers, such as centrosomes. γ-Tubulin, which forms multiprotein complexes, is essential for nucleation. The γ-tubulin ring complex (γ-TuRC) is an efficient microtubule nucleator that requires additional centrosomal proteins for its activation and targeting. Evidence suggests that there is a dysfunction of centrosomal microtubule nucleation in cancer cells. Despite decades of molecular analysis of γ-TuRC and its interacting factors, the mechanisms of microtubule nucleation in normal and cancer cells remains obscure. Here, we review recent work on the high-resolution structure of γ-TuRC, which brings new insight into the mechanism of microtubule nucleation. We discuss the effects of γ-TuRC protein dysregulation on cancer cell behavior and new compounds targeting γ-tubulin. Drugs inhibiting γ-TuRC functions could represent an alternative to microtubule targeting agents in cancer chemotherapy.

TUBA1C is a Prognostic Marker in Low-grade Glioma and Correlates with Immune Cell Infiltration in the Tumor Microenvironment

TUBA1C, a microtubule component, contributes to the development of several cancers. Our purpose was to study the expression of TUBA1C, its potential prognostic value, and its effects on the infiltration of immune cells of low-grade glioma (LGG). Through applying multiple bioinformatics analyses, we extracted and analyzed datasets from TCGA, TIMER, GTEx, GEPIA, and HPA to investigate the potential oncogenic mechanisms of TUBA1C, including the correlation between TUBA1C and prognosis, immune-checkpoints, tumor microenvironment (TME), and infiltration of immune cells in LGG. GO functional annotations and KEGG pathway analyses were further applied to investigate the potential action of TUBA1C in LGG. We revealed that the mRNA levels of TUBA1C were increased in LGG tumor tissues than in normal tissues. Additionally, TUBA1C was up-regulated in the grade III of LGG than in grade II. Moreover, we found that TUBA1C may be an independent prognostic factor of LGG, and high TUBA1C expression correlated to a poor prognosis of LGG. TUBA1C expression was positively associated with the infiltration of B cells, CD8 T+ cells, CD4⁺ T cells, macrophages, dendritic cells, and neutrophils. TUBA1C was also verified to be co-expressed with immune-related genes and immune-checkpoints. GO and KEGG pathway analyses indicated that TUBA1C may potentially regulate the pathogenesis of LGG through immune-related pathways, including chemokine pathway; JAK-STAT pathway; natural killer cell mediated cytotoxicity; T cell receptor pathway; leukocyte migration; negative regulation of immune system process; regulation of lymphocyte activation; T cell activation and other pathways. In conclusion, TUBA1C expression is increased in LGG and high TUAB1C expression is related to a poor prognosis. TUBA1C may influence tumor development by regulating the tumor-infiltrating cells in the TME. TUBA1C may be a potential target for immunotherapy.

Proteolysis of γ-tubulin small complex proteins is mediated by the ubiquitin-proteasome system

Microtubule nucleation is mainly mediated by the γ-tubulin ring complex (γTuRC), whose core components are γ-tubulin and γ-tubulin complex proteins GCP2-6. A substantial fraction of γ-tubulin also exists with GCP2 and GCP3 in a tetramer called the γ-tubulin small complex (γTuSC). To date, the mechanisms underlying the turnover of γ-tubulin and GCPs have remained unclear. Here, we show that γ-tubulin, GCP2, and GCP3 are proteolyzed by the ubiquitin-proteasome system, and we identify cullin 1, cullin 4A, and cullin 4B as the E3 ligases that mediate the ubiquitination and, consequently, the degradation of γ-tubulin. Notably, we found that γTuSC disassembly promotes the degradation of γ-tubulin, GCP2, and GCP3, which indicates a role for γTuSCs in the stabilization of its components.

Prognostic biomarker TUBA1C is correlated to immune cell infiltration in the tumor microenvironment of lung adenocarcinoma

BACKGROUND

TUBA1C is a microtubule component that is involved in a variety of cancers. Our main objective was to investigate TUBA1C expression, its prognostic value, its potential biological functions, and its impact on the immune system of patients with lung adenocarcinoma (LUAD).

METHODS

The Cancer Genome Atlas (TCGA), Gene Expression Profiling Interactive Analysis (GEPIA) and Immunohistochemistry Analysis were used to analyze TUBA1C expression, its clinicopathology, overall survival (OS), and disease-free survival (DFS) in LUAD patients. We also determined the correlation between TUBA1C and tumor-infiltrating immune cells (TIICs) by using CIBERSORT and GEPIA databases. To determine the expression of TUBA1C in LUAD, we analyzed a collection of immune infiltration levels and cumulative survival of LUAD tissues in TIMER database. By using UALCAN, STRING, and GeneMANIA databases, we investigated the protein-coding genes related to TUBA1C and its co-expression genes in LUAD tissues. Gene set enrichment analysis (GSEA) was performed by using the TCGA dataset.

RESULTS

The mRNA and the protein expression of TUBA1C were found to be up-regulated in LUAD tissues. The univariate analysis indicated that an increased expression of TUBA1C was significantly correlated to the following parameters: age, stage, and lymph node metastasis. An over-expression of TUBA1C was associated with a poor prognosis of LUAD. In TIMER and CIBERSORT databases, we found that TUBA1C is correlated with 13 types of TIICs: activated B cell, activated CD4 T cell, central memory CD4 T cell, effector memory CD8 T cell, eosinophils, immature B cell, gamma-delta T cell, immature dendritic cell, mast cell, memory B cell, natural killer T cell, regulatory T cell, and type 2T helper cell. By performing GSEA, we found that TUBA1C is closely correlated to cell cycle, p53 signaling pathway, glycolysis, and gluconeogenesis.

CONCLUSIONS

Our findings indicate that TUBA1C is associated with TIICs in tumor microenvironment. Therefore, it serves as a novel prognostic biomarker and a target for future treatment methods of LUAD.

Oncogene TUBA1C promotes migration and proliferation in hepatocellular carcinoma and predicts a poor prognosis

The prognostic biomarkers and potential therapy targets are urgently needed in hepatocellular carcinoma (HCC). In this article, we report the expression of TUBA1C was significantly increased in HCC on mRNA and protein level, and this finding was further validated in another two independent datasets. Survival analysis was also implemented on these three datasets, and TUBA1C high expression group was detected to have relative shorter survival time. Furthermore, the metastatic ability is increased along with TUBA1C abundance, according to protein abundance evaluation of normal-tumor-portal vein tumor thrombus pairs, and mRNA comparison between metastasis-averse HCC and metastasis-incline HCC. Correlation analysis was implemented and TUBA1C expression was shown to be significantly associated with recurrence, embolus, and AFP level. Proliferation and migration assays following knock down of TUBA1C in two cell lines, HCCLM3 and PLC, revealed that down-regulation of TUBA1C significantly reduces proliferation and migration in HCC cells. in vivo study also showed the similar results. Gene Set Enrichment Analysis (GSEA) comparing the TUBA1C-low and TUBA1C-high group indicates that KEGG pathways including "cell cycle", "DNA replication", and "proteasome" were significantly enriched in TUBA1C-high group. In conclusion, prognostic biomarker and oncogene TUBA1C promotes migration and proliferation of hepatocellular carcinoma cells, probability via cell cycle signaling pathway.

Blockade of vascular endothelial growth factor receptors by tivozanib has potential anti-tumour effects on human glioblastoma cells

Glioblastoma (GBM) remains one of the most fatal human malignancies due to its high angiogenic and infiltrative capacities. Even with optimal therapy including surgery, radiotherapy and temozolomide, it is essentially incurable. GBM is among the most neovascularised neoplasms and its malignant progression associates with striking neovascularisation, evidenced by vasoproliferation and endothelial cell hyperplasia. Targeting the pro-angiogenic pathways is therefore a promising anti-glioma strategy. Here we show that tivozanib, a pan-inhibitor of vascular endothelial growth factor (VEGF) receptors, inhibited proliferation of GBM cells through a G2/M cell cycle arrest via inhibition of polo-like kinase 1 (PLK1) signalling pathway and down-modulation of Aurora kinases A and B, cyclin B1 and CDC25C. Moreover, tivozanib decreased adhesive potential of these cells through reduction of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Tivozanib diminished GBM cell invasion through impairing the proteolytic cascade of cathepsin B/urokinase-type plasminogen activator (uPA)/matrix metalloproteinase-2 (MMP-2). Combination of tivozanib with EGFR small molecule inhibitor gefitinib synergistically increased sensitivity to gefitinib. Altogether, these findings suggest that VEGFR blockade by tivozanib has potential anti-glioma effects in vitro. Further in vivo studies are warranted to explore the anti-tumour activity of tivozanib in combinatorial approaches in GBM.

Overexpression and Nucleolar Localization of γ-Tubulin Small Complex Proteins GCP2 and GCP3 in Glioblastoma

The expression, cellular distribution, and subcellular sorting of the microtubule (MT)-nucleating γ-tubulin small complex (γTuSC) proteins, GCP2 and GCP3, were studied in human glioblastoma cell lines and in clinical tissue samples representing all histologic grades of adult diffuse astrocytic gliomas (n = 54). Quantitative real-time polymerase chain reaction revealed a significant increase in the expression of GCP2 and GCP3 transcripts in glioblastoma cells versus normal human astrocytes; these were associated with higher amounts of both γTuSC proteins. GCP2 and GCP3 were concentrated in the centrosomes in interphase glioblastoma cells, but punctate and diffuse localizations were also detected in the cytosol and nuclei/nucleoli. Nucleolar localization was fixation dependent. GCP2 and GCP3 formed complexes with γ-tubulin in the nucleoli as confirmed by reciprocal immunoprecipitation experiments and immunoelectron microscopy. GCP2 and GCP3 depletion caused accumulation of cells in G2/M and mitotic delay but did not affect nucleolar integrity. Overexpression of GCP2 antagonized the inhibitory effect of the CDK5 regulatory subunit-associated tumor suppressor protein 3 (C53) on DNA damage G2/M checkpoint activity. Tumor cell GCP2 and GCP3 immunoreactivity was significantly increased over that in normal brains in glioblastoma samples; it was also associated with microvascular proliferation. These findings suggest that γTuSC protein dysregulation in glioblastomas may be linked to altered transcriptional checkpoint activity or interaction with signaling pathways associated with a malignant phenotype.

Emerging microtubule targets in glioma therapy

Major advances in the genomics and epigenomics of diffuse gliomas and glioblastoma to date have not been translated into effective therapy, necessitating pursuit of alternative treatment approaches for these therapeutically challenging tumors. Current knowledge of microtubules in cancer and the development of new microtubule-based treatment strategies for high-grade gliomas are the topic in this review article. Discussed are cellular, molecular, and pharmacologic aspects of the microtubule cytoskeleton underlying mitosis and interactions with other cellular partners involved in cell cycle progression, directional cell migration, and tumor invasion. Special focus is placed on (1) the aberrant overexpression of βIII-tubulin, a survival factor associated with hypoxic tumor microenvironment and dynamic instability of microtubules; (2) the ectopic overexpression of γ-tubulin, which in addition to its conventional role as a microtubule-nucleating protein has recently emerged as a transcription factor interacting with oncogenes and kinases; (3) the microtubule-severing ATPase spastin and its emerging role in cell motility of glioblastoma cells; and (4) the modulating role of posttranslational modifications of tubulin in the context of interaction of microtubules with motor proteins. Specific antineoplastic strategies discussed include downregulation of targeted molecules aimed at achieving a sensitization effect on currently used mainstay therapies. The potential role of new classes of tubulin-binding agents and ATPase inhibitors is also examined. Understanding the cellular and molecular mechanisms underpinning the distinct behaviors of microtubules in glioma tumorigenesis and drug resistance is key to the discovery of novel molecular targets that will fundamentally change the prognostic outlook of patients with diffuse high-grade gliomas.