Bioinformatic analysis of the clinicopathological and prognostic significance of oocyte-arresting BTG4 mRNA expression in gynecological cancers

BTG4 arrests the cell cycle and suppresses oocyte and embryonic development. We performed a bioinformatic analysis of BTG4 expression. BTG4 expression was downregulated in breast cancer compared with normal tissues (p < .05), but the opposite was observed in cervical, endometrial and ovarian cancers (p < .05). BTG4 methylation was negatively correlated with its mRNA expression in breast, cervical and endometrial cancers (p < .05). BTG4 mRNA expression was negatively correlated with T staging and distant metastasis of breast cancer; and with tumor invasion, clinical stage, low weight and BMI, low histological grade and no diabetes in endometrial cancer but positively with T stage and non-keratinizing squamous carcinoma in endometrial cancer. BTG4 expression was negatively correlated with the survival of ovarian cancer patients (p < .05), but positively for breast, cervical and endometrial cancers (p < .05). BTG4 expression is thus a potential marker reflecting the carcinogenesis, aggressiveness and prognosis in gynecological cancers.Impact StatementWhat is already known on this subject? Previous studies have revealed the structure and location of BTG4. BTG4 inhibit cell proliferative, promote apoptosis, induce G1 cell cycle arrest. BTG4 promotes the development of mouse embryos from cell stage 1 to 2. The methylation and biological function of BTG4 were clarified in gastric and/or colorectal cancer cells.What do the results of this study add? BTG4 is found to closely link to reflect the carcinogenesis, histogenesis, aggressive behaviors and prognosis of gynecological cancers, and involved in ligand-receptor interaction, microtubule motor activity, dynein light chain binding, cilium organization, assembly, and movement in endometrial and ovarian cancers.What are the implications of these finding for clinical practice and/or further research? Aberrant BTG4 mRNA expression can be employed as a marker of the tumorigenesis, histogenesis, aggressiveness and prognosis of gynecological cancers in the future practice and guide the investigation of BTG4-related signal pathways.

The MIR34B/C genomic region contains multiple potential regulators of multiciliogenesis

The MIR449 genomic locus encompasses several regulators of multiciliated cell formation (multiciliogenesis). The miR-449 homologues miR-34b/c represent additional regulators of multiciliogenesis that are transcribed from another locus. Here, we characterized the expression of BTG4, LAYN and HOATZ, located in the MIR34B/C locus using single-cell RNA-seq and super-resolution microscopy from human, mouse or pig multiciliogenesis models. BTG4, LAYN and HOATZ transcripts were expressed in both precursors and mature multiciliated cells. The Layilin/LAYN protein was absent from primary cilia, but it was expressed in apical membrane regions or throughout motile cilia. LAYN silencing altered apical actin cap formation and multiciliogenesis. HOATZ protein was detected in primary cilia or throughout motile cilia. Altogether, our data suggest that the MIR34B/C locus may gather potential actors of multiciliogenesis.

A novel homozygous C-terminal deletion in BTG4 causes zygotic cleavage failure and female infertility

PURPOSE

We aimed to identify pathogenic variants in a female patient with primary infertility and recurrent failure of in vitro fertilization with zygotic cleavage failure.

METHODS

The genomic DNA from the affected individual was subjected to whole-exome sequencing and the variant was confirmed by Sanger sequencing. The functional effect of the identified variant was further investigated in 293 T cells.

RESULTS

We identified a novel homozygous deletion in BTG4 (c.580_616del) in the affected individual. The deletion results in frameshift and replacement of the last 29 residues (aa195-223) with 66 random amino acids. The mutated amino acid residues are highly conserved among mammalian species. Co-immunoprecipitation in 293 T cells showed that the mutation abolished the interaction between BTG4 and PABPN1L.

CONCLUSION

This study conforms previous studies and expands the mutational spectrum of BTG4. Our findings prove the functional importance of the C-terminal of BTG4. BTG4 is a potential diagnostic and therapeutic target for patients suffering from zygotic cleavage failure.

A novel homozygous missense variant in BTG4 causes zygotic cleavage failure and female infertility

PURPOSE

"Zygotic cleavage failure" is an embryonic phenotype that causes female infertility and failure of in vitro fertilization and/or intracytoplasmic sperm injection. We aimed to identify pathogenic variants in a female infertility patient from a consanguineous family with the "zygotic cleavage failure" phenotype.

METHODS

Whole-exome sequencing was performed in the affected patient; Sanger sequencing was used to confirm the identified variant. The functional effect of the identified variant was further investigated in HeLa cells.

RESULTS

We identified a novel homozygous missense mutation in BTG4 (c.285G > C, p.W95C) in the affected individual. Co-immunoprecipitation in HeLa cells showed the complete loss of the interaction between the p.W95C BTG4 variant protein and CNOT7.

CONCLUSION

This study confirms our previous research and expands the mutational spectrum of BTG4. Our findings complement the diagnostic genetic basis for "zygotic cleavage failure" patients and suggest that BTG4 may be a good target for future therapeutic strategies.

Homozygous Mutations in BTG4 Cause Zygotic Cleavage Failure and Female Infertility

Zygotic cleavage failure (ZCF) is a unique early embryonic phenotype resulting in female infertility and recurrent failure of in vitro fertilization (IVF) and/or intracytoplasmic sperm injection (ICSI). With this phenotype, morphologically normal oocytes can be retrieved and successfully fertilized, but they fail to undergo cleavage. Until now, whether this phenotype has a Mendelian inheritance pattern and which underlying genetic factors play a role in its development remained to be elucidated. B cell translocation gene 4 (BTG4) is a key adaptor of the CCR4-NOT deadenylase complex, which is involved in maternal mRNA decay in mice, but no human diseases caused by mutations in BTG4 have previously been reported. Here, we identified four homozygous mutations in BTG4 (GenBank: NM_017589.4) that are responsible for the phenotype of ZCF, and we found they followed a recessive inheritance pattern. Three of them-c.73C>T (p.Gln25Ter), c.1A>G (p.?), and c.475_478del (p.Ile159LeufsTer15)-resulted in complete loss of full-length BTG4 protein. For c.166G>A (p.Ala56Thr), although the protein level and distribution of mutant BTG4 was not altered in zygotes from affected individuals or in HeLa cells, the interaction between BTG4 and CNOT7 was abolished. In vivo studies further demonstrated that the process of maternal mRNA decay was disrupted in the zygotes of the affected individuals, which provides a mechanistic explanation for the phenotype of ZCF. Thus, we provide evidence that ZCF is a Mendelian phenotype resulting from mutations in BTG4. These findings contribute to our understanding of the role of BTG4 in human early embryonic development and provide a genetic marker for female infertility.

BTG4 is A Novel p53 Target Gene That Inhibits Cell Growth and Induces Apoptosis

BTG4 is the last cloned and poorly studied member of BTG/Tob family. Studies have suggested that BTG4 is critical for the degradation of maternal mRNAs in mice during the process of maternal-to-zygotic transition, and downregulated in cancers, such as gastric cancer. However, the regulatory mechanism of BTG4 and its function in cancers remain elusive. In this study, we have for the first time identified the promoter region of the human BTG4 gene. Serial luciferase reporter assay demonstrated that the core promoter of BTG4 is mainly located within the 388 bp region near its transcription initiation site. Transcription factor binding site analysis revealed that the BTG4 promoter contains binding sites for canonical transcription factors, such as Sp1, whereas its first intron contains two overlapped consensus p53 binding sites. However, overexpression of Sp1 has negligible effects on BTG4 promoter activity, and site-directed mutagenesis assay further suggested that Sp1 is not a critical transcription factor for the transcriptional regulation of BTG4. Of note, luciferase assay revealed that one of the intronic p53 binding sites is highly responsive to p53. Both exogenous p53 overexpression and adriamycin-mediated endogenous p53 activation result in the transcriptional upregulation of BTG4. In addition, BTG4 is downregulated in lung and colorectal cancers, and overexpression of BTG4 inhibits cell growth and induces apoptosis in cancer cells. Taken together, our results strongly suggest that BTG4 is a novel p53-regulated gene and probably functions as a tumor suppressor in lung and colorectal cancers.

Gene methylation in gastric cancer

Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide. Over 70% of new cases and deaths occur in developing countries. In the early years of the molecular biology revolution, cancer research mainly focuses on genetic alterations, including gastric cancer. Epigenetic mechanisms are essential for normal development and maintenance of tissue-specific gene expression patterns in mammals. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. Recent advancements in the rapidly evolving field of cancer epigenetics have shown extensive reprogramming of every component of the epigenetic machinery in cancer, including DNA methylation, histone modifications, nucleosome positioning, noncoding RNAs, and microRNAs. Aberrant DNA methylation in the promoter regions of gene, which leads to inactivation of tumor suppressor and other cancer-related genes in cancer cells, is the most well-defined epigenetic hallmark in gastric cancer. The advantages of gene methylation as a target for detection and diagnosis of cancer in biopsy specimens and non-invasive body fluids such as serum and gastric washes have led to many studies of application in gastric cancer. This review focuses on the most common and important phenomenon of epigenetics, DNA methylation, in gastric cancer and illustrates the impact epigenetics has had on this field.