Six2 is negatively correlated with good prognosis and decreases 5-FU sensitivity via suppressing E-cadherin expression in hepatocellular carcinoma cells

NIK-mediated reactivation of SIX2 enhanced the CSC-like traits of hepatocellular carcinoma cells through suppressing ubiquitin-proteasome system

The critical roles of NF-κB Inducing Kinase (NIK) in tumor progression have been elucidated in various tumors; however, its effects on hepatocellular carcinoma (HCC) progression are still confusing. Here, we found that NIK level was upregulated in HCC tissues compared to that of normal tissues, and positively correlated with the levels of cancer stem cell (CSC) markers. Then we established HCC cells with NIK-stable knockdown and found that NIK knockdown suppressed the CSC-like traits of HCC cells through in vivo and in vitro experiments. Mechanistically, we revealed that SIX2 protein level, but not its mRNA level, was significantly reduced in HCC cells with NIK knockdown, which was rescued by MG132 treatment. Furthermore, NIK knockdown promoted the ubiquitination level of SIX2 and decreased its protein stability. Moreover, Six2 overexpression partially reversed the inhibition of NIK knockdown on the CSC-like traits of HCC cells. This study identified a novel NIK/SIX2 axis conferring HCC stemness.

Clinical utility of PDX cohorts to reveal biomarkers of intrinsic resistance and clonal architecture changes underlying acquired resistance to cetuximab in HNSCC

Cetuximab is a widely used drug for treating head and neck squamous cell carcinomas (HNSCCs); however, it provides restricted clinical benefits, and its response duration is limited by drug resistance. Here, we conducted randomized “Phase II-like clinical trials” of 49 HNSCC PDX models and reveal multiple informative biomarkers for intrinsic resistance to cetuximab (e.g., amplification of ANKH, up-regulation of PARP3). After validating these intrinsic resistance biomarkers in another HNSCC PDX cohort (61 PDX models), we generated acquired cetuximab resistance PDX models and analyzed them to uncover resistance mechanisms. Whole exome sequencing and transcriptome sequencing revealed diverse patterns of clonal selection in acquired resistant PDXs, including the emergence of subclones with strongly activated RAS/MAPK. Extending these insights, we show that a combination of a RAC1/RAC3 dual-target inhibitor and cetuximab could overcome acquired cetuximab resistance in vitro and in vivo. Beyond revealing intrinsic resistance biomarkers, our PDX-based study shows how clonal architecture changes underlying acquired resistance can be targeted to expand the therapeutic utility of this important drug to more HNSCC patients.

The SIX Family of Transcription Factors: Common Themes Integrating Developmental and Cancer Biology

The sine oculis (SIX) family of transcription factors are key regulators of developmental processes during embryogenesis. Members of this family control gene expression to promote self-renewal of progenitor cell populations and govern mechanisms of cell differentiation. When the function of SIX genes becomes disrupted, distinct congenital defects develops both in animal models and humans. In addition to the embryonic setting, members of the SIX family have been found to be critical regulators of tumorigenesis, promoting cell proliferation, epithelial-to-mesenchymal transition, and metastasis. Research in both the fields of developmental biology and cancer research have provided an extensive understanding of SIX family transcription factor functions. Here we review recent progress in elucidating the role of SIX family genes in congenital disease as well as in the promotion of cancer. Common themes arise when comparing SIX transcription factor function during embryonic and cancer development. We highlight the complementary nature of these two fields and how knowledge in one area can open new aspects of experimentation in the other.

Six2 promotes non-small cell lung cancer cell stemness via transcriptionally and epigenetically regulating E-cadherin

OBJECTIVES

The roles and related mechanisms of six2 in regulating non-small cell lung cancer (NSCLC) cells progression are unclear. This work aimed to explore the roles of six2 in NSCLC cell stemness.

MATERIALS AND METHODS

Kaplan-Meier plotter analysis was used to examine the correlation between six2 expression and the survival of NSCLC patients. Quantitative reverse transcription PCR and Western blot were performed to detect six2 expression in clinical samples. Moreover, transwell migration, tumour spheroid formation and in vivo tumour formation assays were used to examine the effects of six2 on NSCLC cell progression. Additionally, methylation analysis was carried out to measure E-cadherin methylation level in different cells. Finally, cell viability assay was performed to explore the effects of six2 on chemotherapeutic sensitivity of NSCLC cells.

RESULTS

Lung cancer patients with a higher six2 expression level displayed a shorter overall survival. Six2 expression was higher in lung cancer tissues than in normal adjacent tissues. Additionally, six2 knockdown suppressed NSCLC cell stemness. Mechanistically, six2 overexpression inhibited epithelial marker E-cadherin expression via stimulating its promoter methylation. And E-cadherin knockdown rescued six2 knockdown-induced decrease of NSCLC cancer cell stemness. Notably, six2 knockdown enhanced cisplatin sensitivity in parental NSCLC cells and attenuated cisplatin resistance in cisplatin-resistant NSCLC cells.

CONCLUSIONS

Our results suggest that six2 facilitates NSCLC cell stemness and attenuates chemotherapeutic sensitivity via suppressing E-cadherin expression.

PPARG Negatively Modulates Six2 in Tumor Formation of Clear Cell Renal Cell Carcinoma

Substantial research has revealed that peroxisome proliferator-activated receptor-gamma (PPARG) plays a critical role in glucose homeostasis and lipid metabolism, and recent studies have shown different effects in the progression of different tumors. However, the role of PPARG and its target gene in clear cell renal cell carcinoma (ccRCC) are incompletely understood. Clinical data revealed abnormal glucolipid metabolism in primary ccRCC samples. In addition, transcriptional profiling indicated that PPARG expression was positively correlated, whereas Six2 expression was negatively correlated with the overall survival of ccRCC patients. Staining showed that PPARG was mainly expressed in tumor cell cytoplasm, and Six2 was localized to the nuclei. In a ccRCC cell line, PPARG activation promoted cell apoptosis, inhibited cell migration and proliferation, and reduced Six2 expression. Mechanistically, overexpressing Six2 downregulated E-cadherin expression and cell apoptosis, but PPARG activation reversed those effects. Taken together, PPARG promotes apoptosis and suppresses the migration and proliferation of ccRCC cells by inhibiting Six2. These findings reveal that the PPARG/Six2 axis acts as a central pathobiological mediator of ccRCC formation and as a potential therapeutic target for the treatment of patients with ccRCC.