A biallelic variant of the RNA exosome gene, EXOSC4, associated with neurodevelopmental defects impairs RNA exosome function and translation.

The RNA exosome is an evolutionarily conserved complex required for both precise RNA processing and decay. Pathogenic variants in EXOSC genes, which encode structural subunits of this complex, are linked to several autosomal recessive disorders. Here, we describe a missense allele of the EXOSC4 gene that causes a collection of clinical features in two affected siblings. This missense variant (NM_019037.3: exon3:c.560T>C) changes a leucine residue within a conserved region of EXOSC4 to proline (p.Leu187Pro). The two affected individuals show prenatal growth restriction, failure to thrive, global developmental delay, intracerebral and basal ganglia calcifications, and kidney failure. Homozygosity for the damaging variant was identified by exome sequencing with Sanger sequencing to confirm segregation. To explore the functional consequences of this amino acid change, we modeled EXOSC4-L187P in the corresponding budding yeast protein, Rrp41 (Rrp41-L187P). Cells that express Rrp41-L187P as the sole copy of the essential Rrp41 protein show growth defects. Steady-state levels of both Rrp41-L187P and EXOSC4-L187P are decreased compared to controls, and EXOSC4-L187P shows decreased copurification with other RNA exosome subunits. RNA exosome target transcripts accumulate in rrp41-L187P cells, including the 7S precursor of 5.8S rRNA. Polysome profiles show a decrease in actively translating ribosomes in rrp41-L187P cells as compared to control cells with the incorporation of 7S pre-rRNA into polysomes. This work adds EXOSC4 to the structural subunits of the RNA exosome that have been linked to human disease and defines foundational molecular defects that could contribute to the adverse phenotypes caused by EXOSC pathogenic variants.

RUNX3 exerts tumor-suppressive role through inhibiting EXOSC4 expression.

Breast cancer severely affects women health. 70% of breast cancer are estrogen receptor positive. Breast cancer stem cells are a group of tumor with plasticity, causing tumor relapse and metastasis. RUNX3 is a tumor suppressor frequently inactivated in estrogen receptor positive breast cancer. However, the mechanism of how RUNX3 is involved in the regualation of cancer stem cell traits in estrogen receptor positive breast cancer remains elusive. In this study, we utilized cut-tag assay to investigate the binding profile RUNX3 in BT474 and T47D cell, and confirmed EXOSC4 as the bona-fide target of RUNX3; RUNX3 could bind to the promoter are of EXOSC4 to suppress its expression. Furthermore, EXOSC4 could increase the colony formation, cell invasion and mammosphere formation ability of breast cancer cells and upregulate the the expression of SOX2 and ALDH1. Consistent with these findings, EXOSC4 was associated with poorer survival for Luminal B/Her2 breast cancer patiens. At last, we confirmed that EXOSC4 mediated the tumor suppressive role of RUNX3 in breast cancer cells. In conclusion, we demonstrate that RUNX3 directly binds to the promoter region of EXOSC4, leading to the suppression of EXOSC4 expression and exerting a tumor-suppressive effect in estrogen receptor postivive breast cancer cells.

A Biallelic Variant of the RNA Exosome Gene EXOSC4 Causes Translational Defects Associated with a Neurodevelopmental Disorder.

The RNA exosome is an evolutionarily conserved complex required for both precise RNA processing and decay. Mutations in EXOSC genes encoding structural subunits of the complex are linked to several autosomal recessive disorders. Here, we describe a missense allele of the EXOSC4 gene, which causes a collection of clinical features in two affected siblings. This missense mutation (NM_019037.3: exon3:c.560T>C), changes a leucine residue within a highly conserved region of EXOSC4 to proline (p.Leu187Pro). The two affected individuals presented with prenatal growth restriction, failure to thrive, global developmental delay, intracerebral and basal ganglia calcifications, and kidney failure. Homozygosity for the damaging variant was identified through exome sequencing and Sanger sequencing confirmed segregation. To explore the functional consequences of this amino acid change, we modeled EXOSC4-L187P in the corresponding budding yeast protein, Rrp41 (Rrp41-L187P). Cells that express Rrp41-L187P as the sole copy of the essential Rrp41 protein show significant growth defects. The steady-state level of both the Rrp41-L187P and the EXOSC4-L187P proteins is significantly decreased compared to control Rrp41/EXOSC4. Consistent with this observation, targets of the RNA exosome accumulate in rrp41-L187P cells, including the 7S precursor of 5.8S rRNA. Polysome profiles show a significant decrease in translation in rrp41-L187P cells as compared to control cells with apparent incorporation of 7S pre-rRNA into polysomes. Taken together, this work adds the EXOSC4 subunit of the RNA exosome to the structural subunits of this complex that have been linked to human disease and defines foundational molecular defects that could contribute to the adverse growth phenotypes caused by this novel EXOSC4 pathogenic variant.

RNA Exosome Component EXOSC4 Amplified in Multiple Cancer Types Is Required for the Cancer Cell Survival.

The RNA exosome is a multi-subunit ribonuclease complex that is evolutionally conserved and the major cellular machinery for the surveillance, processing, degradation, and turnover of diverse RNAs essential for cell viability. Here we performed integrated genomic and clinicopathological analyses of 27 RNA exosome components across 32 tumor types using The Cancer Genome Atlas PanCancer Atlas Studies' datasets. We discovered that the EXOSC4 gene, which encodes a barrel component of the RNA exosome, was amplified across multiple cancer types. We further found that EXOSC4 alteration is associated with a poor prognosis of pancreatic cancer patients. Moreover, we demonstrated that EXOSC4 is required for the survival of pancreatic cancer cells. EXOSC4 also repressed BIK expression and destabilized SESN2 mRNA by promoting its degradation. Furthermore, knockdown of BIK and SESN2 could partially rescue pancreatic cells from the reduction in cell viability caused by EXOSC4 knockdown. Our study provides evidence for EXOSC4-mediated regulation of BIK and SESN2 mRNA in the survival of pancreatic tumor cells.

Exosome Component 4 Promotes Epithelial Ovarian Cancer Cell Proliferation, Migration, and Invasion via the Wnt Pathway.

BACKGROUND: Of gynecologic malignancies, ovarian cancer is the leading cause of death, mainly due to the lack of sensitive tumor markers, which means it almost always presents at an advanced stage. Exosome Component 4 (EXOSC4) is involved in RNA degradation, but its role in epithelial ovarian cancer (EOC) is unclear. METHODS: The expression levels of EXOSC4 in EOC and normal ovarian tissue specimens were determined by immunohistochemical staining. The overall survival (OS) and progression-free survival (PFS) of patients with EOC were evaluated after patients were classified into high and low EXOSC4 expression groups, and the Cox regression model was established to identify independent predictors of patient prognosis. The effects of EXOSC4 on proliferation, colony formation, migration, and invasion were examined in the SKOV-3 and HO8910 cell lines by lentivirus-mediated shRNA knockdown. Flow cytometry was used to detect cell cycle changes. The mRNA levels of cyclin D1, CDK4, and c-myc were detected by RT-PCR. The protein expression levels of ß-catenin, cyclin D1, CDK4, c-myc, vimentin, N-cadherin, and E-cadherin were assessed by western blot. Wnt/ß-catenin activation was measured by TCF/LEF reporter assay. RESULTS: EXOSC4 was significantly elevated in EOC tissues and cell lines. High EXOSC4 expression was correlated with the International Federation of Gynecology and Obstetrics (FIGO) stage and pathological grade, and identified as an independent predictor of shorter OS and PFS. EXOSC4 knockdown suppressed proliferation, migration, and invasion in EOC cell lines. Cells were arrested at G0/G1 phase after EXOSC4 knockdown. The mRNA levels of cyclin D1, CDK4, and c-myc were decreased. ß-catenin, cyclin D1, CDK4, c-myc, vimentin, and N-cadherin protein expression levels were reduced, while those of E-cadherin was increased. Wnt/ß-catenin activity was suppressed after the EXOSC4 knockdown. CONCLUSIONS: EXOSC4 is involved in EOC. Knockdown of EXOSC4 can inhibit the proliferation, migration, and invasion ability of EOC by suppressing the Wnt pathway. EXOSC4 is expected to be a novel biomarker and molecular target in EOC.

STX2 drives colorectal cancer proliferation via upregulation of EXOSC4.

AIMS: To explore the biological function and mechanism of Syntaxin2 (STX2) in Colorectal cancer (CRC) proliferation. MAIN METHODS: A series of gain- and loss-of-function analysis were conducted the to explore the biological function of STX2 in CRC proliferation in vivo and in vitro. Western blot, Co-immunoprecipitation (Co-IP) and the functional analyses were taken to analyze the regulative role of STX2 on Exosome Complex 4 (EXOSC4) in CRC proliferation; Immunohistochemistry (IHC) and Real-time quantitative polymerase chain reaction (qPCR) were used to further verify the relationship between the expression of STX2 and EXOSC4 in human CRC samples. KEY FINDINGS: Our study revealed that the over-expression of STX2 promoted CRC proliferation, while knockdown of STX2 repressed CRC proliferation; STX2 promoted CRC proliferation via increasing EXOSC4 protein; There was a positive correlation between STX2 and EXOSC4 expression. SIGNIFICANCE: The current data verify that STX2 drives the proliferation of CRC via increasing the expression of EXOSC4.

EXOSC4 functions as a potential oncogene in development and progression of colorectal cancer.

Colorectal cancer (CRC) is a heterogeneous disease with complex mechanisms of pathogenesis. Classification systems have been proposed based on molecular features of tumors in clinical practice. Thus, more molecular markers associated with development and progression of CRC might serve as useful tools for early diagnosis even for providing more accurate molecular classification. Frequent gain of chromosome 8q was detected in CRC by array-CGH and overexpression of exosome component 4 (EXOSC4) in this region was revealed by expression microarray analysis. Through qRT-PCR and immunohistochemistry (IHC) analysis, EXOSC4 showed increased expression in CRC cell lines and clinical specimens. Higher expression of EXOSC4 was more often detected in left side, and correlated with BRAF wild type, MSI-low or MSS, CIMP-low, and MLH1-no-silence CRC patients. Functionally, EXOSC4 overexpression increased early tumorigenic capacity by promoting cell proliferation and monolayer colony formation, enhancing cell invasion and migration study and accelerating xenograft formation in nude mice. While EXOSC4 knockdown exhibited anti-oncogenic role such as inhibiting cell proliferation and invasion. EXOSC4 inhibition also resulted in G1 phase cell cycle arrest. For the downstream signaling analysis, EXOSC4 was found to be involved in multiple signaling pathways such as cell cycle, p53 pathway and Wnt pathway. In summary, our findings demonstrated the oncogenic role of EXOSC4 in development and progression of CRC. Deep understanding of EXOSC4 as a potential diagnostic molecular biomarker will provide clinical translational potential for intervention therapy.