TUBB4B is a novel therapeutic target in non-alcoholic fatty liver disease-associated hepatocellular carcinoma.

Non-alcoholic fatty liver disease-associated hepatocellular carcinoma (NAFLD-HCC) is an emerging malignancy due to the rising prevalence of NAFLD. However, no drug is available to target NAFLD-HCC. In this study, we aim to unravel novel therapeutic targets of NAFLD-HCC utilizing a high-throughput CRISPR/Cas9 screening strategy. We utilized the Epi-drug CRISPR/Cas9 library consisting of single-guide RNAs (sgRNAs) targeting over 1,000 genes representing the FDA-approved drug targets and epigenetic regulators to perform loss-of-function screening in two NAFLD-HCC cell lines (HKCI2 and HKCI10). CRISPR/Cas9 library screening unraveled TUBB4B as an essential gene for NAFLD-HCC cell growth. TUBB4B was overexpressed in NAFLD-HCC tumors compared with adjacent normal tissues (N = 17) and was associated with poor survival (p < 0.01). RNA-sequencing and functional assays revealed that TUBB4B knockout in NAFLD-HCC promoted cell apoptosis, cell cycle arrest, and cellular senescence, leading to suppressed NAFLD-HCC growth in vitro and in vivo. We identified that TUBB4B inhibitor mebendazole (MBZ), an FDA-approved drug, inhibited NAFLD-HCC growth by inducing apoptosis and cellular senescence. Since protein expression of pro-survival Bcl-xL was induced in TUBB4B knockout NAFLD-HCC cells, we examined combination of TUBB4B inhibition with navitoclax, a Bcl-xL inhibitor that selectively targets senescent cells. Consistent with our hypothesis, either TUBB4B knockout or MBZ synergized with navitoclax to inhibit NAFLD-HCC cell growth via the induction of intrinsic and extrinsic apoptosis pathways. In summary, TUBB4B is a novel therapeutic target in NAFLD-HCC. Inhibition of TUBB4B with MBZ in combination with navitoclax synergistically inhibited NAFLD-HCC cell growth, representing a promising strategy for the treatment of NAFLD-HCC. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Mutations in TUBB4B Cause a Distinctive Sensorineural Disease.

Leber congenital amaurosis (LCA) is a neurodegenerative disease of photoreceptor cells that causes blindness within the first year of life. It occasionally occurs in syndromic metabolic diseases and plurisystemic ciliopathies. Using exome sequencing in a multiplex family and three simplex case subjects with an atypical association of LCA with early-onset hearing loss, we identified two heterozygous mutations affecting Arg391 in ß-tubulin 4B isotype-encoding (TUBB4B). Inspection of the atomic structure of the microtubule (MT) protofilament reveals that the ß-tubulin Arg391 residue contributes to a binding pocket that interacts with α-tubulin contained in the longitudinally adjacent αß-heterodimer, consistent with a role in maintaining MT stability. Functional analysis in cultured cells overexpressing FLAG-tagged wild-type or mutant TUBB4B as well as in primary skin-derived fibroblasts showed that the mutant TUBB4B is able to fold, form αß-heterodimers, and co-assemble into the endogenous MT lattice. However, the dynamics of growing MTs were consistently altered, showing that the mutations have a significant dampening impact on normal MT growth. Our findings provide a link between sensorineural disease and anomalies in MT behavior and describe a syndromic LCA unrelated to ciliary dysfunction.

Genetic Deciphering of Early-Onset and Severe Retinal Dystrophy Associated with Sensorineural Hearing Loss.

The specific association of Leber congenital amaurosis (LCA) or early-onset severe retinal dystrophy (LCA-like) with sensorineural hearing loss (SHL) is uncommon. Recently, we ascribed some of these distinctive associations to dominant and de novo mutations in the ß-tubulin 4B isotype-encoding gene (TUBB4B), providing a link between a sensorineural disease and anomalies in microtubules behavior. Here, we report 12 sporadic cases with LCA/SHL or LCA-like/SHL and no TUBB4B mutation. Trio-based whole exome sequencing (WES) identified disease-causing mutations in 5/12 cases. Four out of five carried biallelic mutations in PEX1 (1/4) or PEX6 (3/4), involved in peroxisome biogenesis disorders from Zellweger syndrome characterized by severe neurologic and neurosensory dysfunctions, craniofacial abnormalities, and liver dysfunction to Heimler syndrome associating SHL, enamel hypoplasia of the secondary dentition, nail abnormalities, and occasional retinal disease. Upon reexamination, the index case carrying PEX1 mutations, a 4-year-old girl, presented additional symptoms consistent with Zellweger syndrome. Reexamination of individuals with PEX6 mutations (1/3 unavailable) revealed normal nails but enamel hypoplasia affecting one primary teeth in a 4-year-old girl and severe enamel hypoplasia of primary teeth hidden by dental prosthesis in a 50-year-old male, describing a novel PEX6-associated disease of the Zellweger/Heimler spectrum. Finally, hemizygosity for a CACNA1F mutation was identified in an 18-year-old male addressed for LCA/SHL, redirecting the retinal diagnosis to congenital stationary night blindness (CSNB2A). Consistent with the pure CSNB2A retinal involvement, SHL was ascribed to biallelic mutations in another gene, STRC, involved in nonprogressive DFNB16 deafness.

P300 reduces TUBB4B expression to facilitate the biological process of migration and invasion of non-small cell lung cancer cells.

This article explored the mechanism of E1A binding protein p300 (P300) and beta-tubulin 4B isotype-encoding gene (TUBB4B) in regulating the migration and invasion of non-small cell lung cancer (NSCLC) cells. TUBB4B and P300 expression in NSCLC tissues and cells was monitored by real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot. TUBB4B function on NSCLC cell migration, invasion and epithelial-mesenchymal transition (EMT) was monitored by wound healing assay, Transwell experiment and Western blot. The regulation of P300 on TUBB4B was monitored by qRT-PCR and Western blot. Mechanism of P300 and TUBB4B in regulating NSCLC cell migration and invasion was explored by rescue experiment. A xenograft tumor model was established by using nude mouse. As a result, low TUBB4B expression and high P300 expression was discovered in NSCLC tissues and cells. TUBB4B and P300 expression showed a negative correlation in NSCLC tissues. Lower TUBB4B but higher P300 was observed in tumor tissues of NSCLC patients with metastasis. TUBB4B overexpression suppressed NSCLC cell migration, invasion and EMT. TUBB4B silencing had opposite results. P300 overexpression inhibited TUBB4B expression, and P300 silencing facilitated TUBB4B overexpression in NSCLC cells. TUBB4B overexpression counteracted the promotion of P300 overexpression on NSCLC cell invasion and migration. TUBB4B silencing abrogated the inhibition of P300 knockdown on NSCLC cell invasion and migration. TUBB4B overexpression suppressed NSCLC cell in vivo growth. Thus, TUBB4B could be reduced by P300 in NSCLC. It exerted suppression role on NSCLC cell migration, invasion and EMT. TUBB4B may be a novel target for NSCLC treatment.

Comprehensive analysis of two hotspot codons in the TUBB4B gene and associated phenotypes.

Our purpose was to elucidate the genotype and ophthalmological and audiological phenotype in TUBB4B-associated inherited retinal dystrophy (IRD) and sensorineural hearing loss (SNHL), and to model the effects of all possible amino acid substitutions at the hotspot codons Arg390 and Arg391. Six patients from five families with heterozygous missense variants in TUBB4B were included in this observational study. Ophthalmological testing included best-corrected visual acuity, fundus examination, optical coherence tomography, fundus autofluorescence imaging, and full-field electroretinography (ERG). Audiological examination included pure-tone and speech audiometry in adult patients and auditory brainstem response testing in a child. Genetic testing was performed by disease gene panel analysis based on genome sequencing. The molecular consequences of the substitutions of residues 390 and 391 on TUBB4B and its interaction with α-tubulin were predicted in silico on its three-dimensional structure obtained by homology modelling. Two independent patients had amino acid exchanges at position 391 (p.(Arg391His) or p.(Arg391Cys)) of the TUBB4B protein. Both had a distinct IRD phenotype with peripheral round yellowish lesions with pigmented spots and mild or moderate SNHL, respectively. Yet the phenotype was milder with a sectorial pattern of bone spicules in one patient, likely due to a genetically confirmed mosaicism for p.(Arg391His). Three patients were heterozygous for an amino acid exchange at position 390 (p.(Arg390Gln) or p.(Arg390Trp)) and presented with another distinct retinal phenotype with well demarcated pericentral retinitis pigmentosa. All showed SNHL ranging from mild to severe. One additional patient showed a variant distinct from codon 390 or 391 (p.(Tyr310His)), and presented with congenital profound hearing loss and reduced responses in ERG. Variants at codon positions 390 and 391 were predicted to decrease the structural stability of TUBB4B and its complex with α-tubulin, as well as the complex affinity. In conclusion, the twofold larger reduction in heterodimer affinity exhibited by Arg391 substitutions suggested an association with the more severe retinal phenotype, compared to the substitution at Arg390.

[Expression of TUBB4B in mouse primary spermatocyte GC-2 cells and its regulatory effect on NF-κB and MAPK signaling pathway].

OBJECTIVE: To explore the interaction between Tubulin beta 4B class IVb (TUBB4B) and Agtpbp1/cytosolic carboxypeptidase- like1 (CCP1) in mouse primary spermatocytes (GC-2 cells) and the role of TUBB4B in regulating the development of GC-2 cells. METHODS: Lentiviral vectors were used to infect GC-2 cells to construct TUBB4B knockdown and negative control (NC-KD) cells. The stable cell lines with TUBB4B overexpression (Tubb4b-OE) and the negative control (NC-OE) cells were screened using purinomycin. RT-qPCR and Western blotting were used to verify successful cell modeling and explore the relationship between TUBB4B and CCP1 expressions in GC-2 cells. The effects of TUBB4B silencing and overexpression on the proliferation and cell cycle of GC-2 cells were evaluated using CCK8 assay and flow cytometry. The signaling pathway proteins showing significant changes in response to TUBB4B silencing or overexpression were identified using Western blotting and immunofluorescence assay and then labeled for verification at the cellular level. RESULTS: Both TUBB4B silencing and overexpression in GC-2 cells caused consistent changes in the mRNA and protein expressions of CCP1 (P < 0.05). Similarly, TUBB4B expression also showed consistent changes at the mRNA and protein after CCP1 knockdown and restoration (P < 0.05). TUBB4B knockdown and overexpression had no significant effect on proliferation rate or cell cycle of GC-2 cells, but caused significant changes in the key proteins of the nuclear factor kappa-B (NF-κB) signaling pathway (p65 and p-p65) and the mitogen-activated protein kinase (MAPK) signaling pathway (ErK1/2 and p-Erk1/2) (P < 0.05); CCP1 knockdown induced significant changes in PolyE expression in GC-2 cells (P < 0.05). CONCLUSIONS: TUBB4B and CCP1 interact via a mutual positive regulation mechanism in GC-2 cells. CCP-1 can deglutamize TUBB4B, and the latter is involved in the regulation of NF-κB and MAPK signaling pathways in primary spermatocytes.

Tubulin TUBB4B Is Involved in Spermatogonia Proliferation and Cell Cycle Processes.

Tubb4b (tubulin ß-4b chain) is essential for cell growth and development as a microtubule network protein. Previous studies have shown that TUBB4B affects mouse pronucleus migration, but the gene function has yet to be elucidated. To study TUBB4B-related functions in mouse reproductive development, we designed a single sgRNA in chromosome 2 and generated a knockout spermatogonia cell line of the ß-tubulin isoform Tubb4b by the CRISPR/Cas9 system. Tubb4b-KO spermatogonia recognized abnormal lysosomal membranes and cell morphology defects. Compared to control mouse spermatogonia, the proliferation rate was significantly slower and cycling stagnated in the G1/0 population. Although spermatogonia lacking TUBB4B have abnormal divisions, they are not lethal. We detected the mRNA levels of the cell-regulating cyclins CyclinsD1, CyclinsE, Cdk2, Cdk4, P21, Skp2 and the cell growth factors C/EBP α, C/EBP ß, and G-CSF in the spermatogonia of Tubb4b-KO and found that the expressions of CyclinsD1, Skp2 and cell growth factors were significantly reduced. Further analysis revealed that 675 genes were expressed differently after Tubb4b deletion and were enriched in negative regulation of cell population proliferation (GO:0008285), negative regulation of cell cycle G2/M phase transition (GO:1902750), and positive regulation of cell death (GO: 0010942). We also found that there is a common gene Cdkn1a (P21) in these three GO pathways related to cell proliferation and cell cycle, and both quantitative analysis and transcriptome sequencing results showed that the expression of this gene was up-regulated in Tubb4b knockout cells. This implies that Tubb4b may be involved in the division of spermatogonia with multiple cell cycle regulatory proteins. Overall, these data indicate that Tubb4b has a specific role in regulating spermatogonia proliferation and cell cycle.

TUBB4B gene mutation in Leber phenotype of congenital amaurosis syndrome associated with early-onset deafness.

Beta-tubulin 4B isotype is one of the subunits of microtubules encoded by TUBB4B gene on chromosome 9, which is responsible for the maintenance of microtubule stability. In humans, mutations in microtubule-encoding genes have been associated with several tubulinopathies with very heterogeneous symptoms. So far, only two missense mutations in TUBB4B gene have been found to have pathological implications in this disorder. Here we report a Hungarian family with three affected members, mother and her 12- and 14-year-old children, who suffer from ophthalmologic and hearing impairments probably due to c.1171C > T missense variant in the TUBB4B gene. The presented case is the second report, and unique in the literature because of three affected family members carrying the same mutation and the family provides evidence for a quite similar but not identical phenotype of LCAEOD in subjects carrying this mutation.

ß-Tubulin Isotype, TUBB4B, Regulates The Maintenance of Cancer Stem Cells.

Recent advancements in cancer research have shown that cancer stem cell (CSC) niche is a crucial factor modulating tumor progression and treatment outcomes. It sustains CSCs by orchestrated regulation of several cytokines, growth factors, and signaling pathways. Although the features defining adult stem cell niches are well-explored, the CSC niche is poorly characterized. Since membrane trafficking proteins have been shown to be essential for the localization of critical proteins supporting CSCs, we investigated the role of TUBB4B, a probable membrane trafficking protein that was found to be overexpressed in the membranes of stem cell enriched cultures, in sustaining CSCs in oral cancer. Here, we show that the knockdown of TUBB4B downregulates the expression of pluripotency markers, depletes ALDH1A1+ population, decreases in vitro sphere formation, and diminishes the tumor initiation potential in vivo. As TUBB4B is not known to have any role in transcriptional regulation nor cell signaling, we suspected that its membrane trafficking function plays a role in constituting a CSC niche. The pattern of its expression in tissue sections, forming a gradient in and around the CSCs, reinforced the notion. Later, we explored its possible cooperation with a signaling protein, Ephrin-B1, the abrogation of which reduces the self-renewal of oral cancer stem cells. Expression and survival analyses based on the TCGA dataset of head and neck squamous cell carcinoma (HNSCC) samples indicated that the functional cooperation of TUBB4 and EFNB1 results in a poor prognosis. We also show that TUBB4B and Ephrin-B1 cohabit in the CSC niche. Moreover, depletion of TUBB4B downregulates the membrane expression of Ephrin-B1 and reduces the CSC population. Our results imply that the dynamics of TUBB4B is decisive for the surface localization of proteins, like Ephrin-B1, that sustain CSCs by their concerted signaling.