Dimerization and Transactivation Domains as Candidates for Functional Modulation and Diversity of Sox9

SOX9 promotes the invasion and migration of lung adenocarcinoma cells by activating the RAP1 signaling pathway

OBJECTIVE

SOX9 has been shown to be related to the metastasis of various cancers. Recently, it has been reported that SOX9 plays a regulatory role in lung adenocarcinoma (LUAD) cell metastasis, but the specific mechanism remains to be explored. Therefore, the objective of this study was to observe the effect and mechanism of SOX9 on the invasion and migration of LUAD cells.

METHODS

RT-qPCR was applied to observe the expression of SOX9 and RAP1 in tumor tissues and corresponding normal lung tissues collected from LUAD patients. Co-immunoprecipitation and Pearson correlation to analyze the expression correlation of SOX9 with RAP1. To observe the role of SOX9, the invasion and migration levels of LUAD A549 cells in each group were observed by Transwell invasion assay and Scratch migration assay after knocking down or overexpressing SOX9. Besides, the expression levels of RAP1 pathway-related proteins (RAP1, RAP1GAP and RasGRP33) were observed by RT-qCPR or western blot. Subsequently, RAP1 was overexpressed and SOX9 was knocked down in A549 cells, and then the cell invasion/migration level and RAP1 pathway activity were assessed.

RESULTS

The expression levels of SOX9 and RAP1 in tumor tissues and A549 cells of LUAD patients were significantly increased and positively correlated. Overexpression of SOX9 or RAP1 alone in A549 cells enhanced the invasion and migration ability of cells, as well as up-regulated the expression levels of RAP1, RAP1GAP and RasGRP33. However, knocking down SOX9 decreased cell invasion and migration levels and weakened the activity of RAP1 pathway. Notably, overexpressing RAP1 while knocking down SOX9 significantly activated RAP1 pathway and promoted cell invasion and migration.

CONCLUSION

Overexpression of SOX9 in LUAD can significantly activate the RAP1 signaling pathway and promote cell invasion and migration.

Variants in the SOX9 transactivation middle domain induce axial skeleton dysplasia and scoliosis

SOX9 is an essential transcriptional regulator of cartilage development and homeostasis. In humans, dysregulation of SOX9 is associated with a wide spectrum of skeletal disorders, including campomelic and acampomelic dysplasia, and scoliosis. The mechanism of how SOX9 variants contribute to the spectrum of axial skeletal disorders is not well understood. Here, we report four novel pathogenic variants of SOX9 identified in a large cohort of patients with congenital vertebral malformations. Three of these heterozygous variants are in the HMG and DIM domains, and for the first time, we report a pathogenic variant within the transactivation middle (TAM) domain of SOX9 . Probands with these variants exhibit variable skeletal dysplasia, ranging from isolated vertebral malformation to acampomelic dysplasia. We also generated a Sox9 hypomorphic mutant mouse model bearing a microdeletion within the TAM domain ( Sox9 ^Asp272del ). We demonstrated that disturbance of the TAM domain with missense mutation or microdeletion results in reduced protein stability but does not affect the transcriptional activity of SOX9. Homozygous Sox9 ^Asp272del mice exhibited axial skeletal dysplasia including kinked tails, ribcage anomalies, and scoliosis, recapitulating phenotypes observed in human, while heterozygous mutants display a milder phenotype. Analysis of primary chondrocytes and the intervertebral discs in Sox9 ^Asp272del mutant mice revealed dysregulation of a panel of genes with major contributions of the extracellular matrix, angiogenesis, and ossification-related processes. In summary, our work identified the first pathologic variant of SOX9 within the TAM domain and demonstrated that this variant is associated with reduced SOX9 protein stability. Our finding suggests that reduced SOX9 stability caused by variants in the TAM domain may be responsible for the milder forms of axial skeleton dysplasia in humans.

Novel SRY-box transcription factor 9 variant in campomelic dysplasia and the location of missense and nonsense variants along the protein domains: A case report

BACKGROUND

Campomelic dysplasia (CD) is a rare disorder that involves the skeletal and genital systems. This condition has been associated with a diverse set of mutations in the SRY-box transcription factor 9 (SOX9) gene.

CASE PRESENTATION

We herein report a case involving a 4-year-old female patient with CD, female sex reversal, type 1 Arnold-Chiari malformation, and bilateral conductive hearing loss and investigate the causal mutation. Whole-exome sequencing analysis detected a novel Trp115X* variant in the SOX9 gene. We performed a literature review of the reported cases and demonstrated that the missense variants were located only in the self-dimerization domain (DIM) and high-mobility group box domains. We also reported that variants in the DIM domain do not cause sex reversal and identified that the amino acid sequences that were mutated in the patients with campomelic dysplasia are evolutionarily conserved among primates.

CONCLUSIONS

We suggest that missense variants cannot be located in the K2, PQA, and PQS given that these domains function critically for transcriptional activation or repression of target genes and evolve under purifying selection.

SOX9 promotes epidermal growth factor receptor-tyrosine kinase inhibitor resistance via targeting β-catenin and epithelial to mesenchymal transition in lung cancer

AIMS

The first-generation epidermal growth factor receptor-tyrosine kinase inhibitor (EGFR-TKI), gefitinib, continues to be a primary treatment option for lung cancer patients. However, acquisition of resistance to gefitinib is a major obstacle in lung cancer treatment and its cause is poorly understood. The present study aimed to implicate the role of SOX9-β-catenin in developed resistance to gefitinib through epithelial to mesenchymal transition (EMT) in lung cancer in vitro and ex vivo.

MAIN METHODS

Expression effect of SOX9 on survivability of lung cancer patients was demonstrated through online available Kaplan-Meier Plotter data base. Then, cell viability assay, colony forming assay, cell migration and invasion assays, flow cytometry, drug efflux assay, qRT-PCR, and western blotting were conducted to confirmed the role of SOX9 in gefitinib resistance in lung cancer cells. Dual-luciferase assay established the regulatory relation between SOX9 and β-catenin. Multicellular spheroid assay further explored that down regulation of SOX9 could reverse gefitinib resistance ex vivo.

KEY FINDINGS

Kaplan-Meier method correlated the higher expression of SOX9 and β-catenin with poor overall survival of lung cancer patients. Upregulation of SOX9 was associated gefitinib resistance with increased cell proliferation, migration and invasion, single-cell colony-forming ability, reduced apoptosis, and gefitinib intake in lung cancer cells. Moreover, upregulated SOX9 promoted EMT via targeting β-catenin and knockdown of SOX9 reversed the resistance and EMT phenotype. Similarly, we found that multicellular spheroid of gefitinib resistant cells showed larger surface area with more dispersion and viability of cells, while SOX9 knockdown abolished these induced properties ex vivo.

SIGNIFICANCE

SOX9 expression could provide an innovative perspective as biomarker to understand the EGFR-TKIs resistance in lung cancer.

SOX9 modulates cancer biomarker and cilia genes in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive form of cancer with high mortality. The cellular origins of PDAC are largely unknown; however, ductal cells, especially centroacinar cells (CACs), have several characteristics in common with PDAC, such as expression of SOX9 and components of the Notch-signaling pathway. Mutations in KRAS and alterations to Notch signaling are common in PDAC, and both these pathways regulate the transcription factor SOX9. To identify genes regulated by SOX9, we performed siRNA knockdown of SOX9 followed by RNA-seq in PANC-1s, a human PDAC cell line. We report 93 differentially expressed (DE) genes, with convergence on alterations to Notch-signaling pathways and ciliogenesis. These results point to SOX9 and Notch activity being in a positive feedback loop and SOX9 regulating cilia production in PDAC. We additionally performed ChIP-seq in PANC-1s to identify direct targets of SOX9 binding and integrated these results with our DE gene list. Nine of the top 10 downregulated genes have evidence of direct SOX9 binding at their promoter regions. One of these targets was the cancer stem cell marker EpCAM. Using whole-mount in situ hybridization to detect epcam transcript in zebrafish larvae, we demonstrated that epcam is a CAC marker and that Sox9 regulation of epcam expression is conserved in zebrafish. Additionally, we generated an epcam null mutant and observed pronounced defects in ciliogenesis during development. Our results provide a link between SOX9, EpCAM and ciliary repression that can be exploited in improving our understanding of the cellular origins and mechanisms of PDAC.

SOX9: An emerging driving factor from cancer progression to drug resistance

Dysregulation of transcription factors is one of the common problems in the pathogenesis of human cancer. Among them, SOX9 is one of the critical transcription factors involved in various diseases, including cancer. The expression of SOX9 is regulated by microRNAs (miRNAs), methylation, phosphorylation, and acetylation. Interestingly, SOX9 acts as a proto-oncogene or tumor suppressor gene, relying upon kinds of cancer. Recent studies have reported the critical role of SOX9 in the regulation of the tumor microenvironment (TME). Additionally, activation of SOX9 signaling or SOX9 regulated signaling pathways play a crucial role in cancer development and progression. Accumulating evidence also suggests that SOX9 acquires stem cell features to induce epithelial-mesenchymal transition (EMT). Moreover, SOX9 has been broadly studied in the field of cancer stem cell (CSC) and EMT in the last decades. However, the link between SOX9 and cancer drug resistance has only recently been discovered. Furthermore, its differential expression could be a potential biomarker for tumor prognosis and progression. This review outlined the various biological implications of SOX9 in cancer progression and cancer drug resistance and elucidated its signaling network, which could be a potential target for designing novel anticancer drugs.

A Recurrent Rare SOX9 Variant (M469V) is Associated with Congenital Vertebral Malformations

OBJECTIVE

The genetic variations contributed to a substantial proportion of congenital vertebral malformations (CVM). SOX9 gene, a member of the SOX gene family, has been implicated in CVM. To study the SOX9 mutation in CVM patients is of great significance to explain the pathogenesis of scoliosis (the clinical manifestation of CVM) and to explore the pathogenesis of SOX9-related skeletal deformities.

METHODS

A total of 50 singleton patients with CVM were included in this study. Exome Sequencing (ES) was performed on all the patients. The recurrent candidate variant of SOX9 gene was validated by Sanger sequencing. Luciferase assay was performed to investigate the functional changes of this variant.

RESULTS

A recurrent rare heterozygous missense variant in SOX9 gene (NM_000346.3: c.1405A>G, p.M469V) which had not been reported previously was identified in three CVM patients who had the clinical findings of congenital scoliosis without deformities in other systems. This variant was absent from our in-house database and it was predicted to be deleterious (CADD = 24.5). The luciferase assay demonstrated that transactivation capacity of the mutated SOX9 protein was significantly lower than that of the wild-type for the two luciferase reporters (p = 0.0202, p = 0.0082, respectively).

CONCLUSION

This SOX9 mutation (p.M469V) may contribute to CVM without other systematic deformity, which provides important implications and better understanding of phenotypic variability in SOX9-related skeletal deformities.