Identification of a p53-repressed gene module in breast cancer cells

ZNF667-AS1, a positively regulating MEGF10, inhibits the progression of uveal melanoma by modulating cellular aggressiveness

Zinc finger protein 667-antisense RNA 1 (ZNF667-AS1) is a member of the C₂ H₂ zinc finger protein family. However, the exact effect of ZNF667-AS1 in uveal melanoma (UM) progression has not been elucidated. The biological roles of ZNF667-AS1 and MEGF10 were assessed using cell counting kit-8 and flow cytometry. Quantitative reverse-transcription polymerase chain reaction and Western blot analyses were conducted to measure the expression of subjects. ZNF667-AS1 expression was significantly decreased in metastasized UM tissues and its low expression was related to poorer prognosis of UM patients. MEGF10 expression was positively associated with ZNF667-AS1 expression. The inhibitory effect of ZNF667-AS1 overexpression on UM cellular malignant behaviors could be reversed by MEGF10 knockdown, which was re-ascertained by the detection of corresponding protein levels (p53, cyclin D1, Bcl-2, and Bax). In conclusion, ZNF667-AS1 might play an inhibitory role in the development of UM by regulating cellular aggressiveness, which was partially realized by positively regulating MEGF10.

Parthenolide inhibits the proliferation and induces the apoptosis of human uveal melanoma cells

AIM

To explore the effect of parthenolide (PTL) on human uveal melanoma (UM) cells (C918 and SP6.5 cells) and its molecular mechanism.

METHODS

Carboxyfluorescein succinimidyl amino ester (CFSE) assays and cell counting kit-8 (CCK-8) were performed to detect the cell viability. Flow cytometry was used to analyze cell cycle and apoptosis. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot assays were performed to measure proliferation-related and apoptosis-related factors.

RESULTS

Firstly, PTL decreased the viability of C918 and SP6.5 cells in a dose-dependent manner, and the effect of PTL on C918 cells was stronger than on SP6.5; however, it did not affect normal cells. Secondly, PTL increased the proportion of cell number at cell cycle G1 phase in C918 cells, and decreased the proportion of cell number at S phase, but the proportion did not change at G2 phase. In addition, PTL induced the apoptosis of C918 cells, and decreased the expressions of Cyclin D1, B-cell lymphoma-2 (Bcl-2) and B-cell lymphoma-extra large (Bcl-XL). Also, PTL increased Cyclin inhibition protein 1 (P21), Bcl-2-associated X protein (Bax), Cysteinyl aspartate specific proteinas-3 (Caspase-3) and Caspase-9 expression. However, the expression of Caspase-8 was not changed.

CONCLUSION

PTL inhibites proliferation and induces apoptosis in UM cells by arresting G1 phase and regulating mitochondrial pathway, however, it does not affect normal cells.

INKA2, a novel p53 target that interacts with the serine/threonine kinase PAK4

The p53 protein is a tumour suppressor and transcription factor that regulates the expression of target genes involved in numerous stress responses systems. In this study, we designed a screening strategy using DNA damage-induced mouse and human transcriptome data to identify novel downstream targets of p53. Our method selected genes with an induced expression in multiple organs of X-ray-irradiated p53 wild-type mice. The expression of inka box actin regulator 2 gene, known as Inka2, was upregulated in 12 organs when p53 expression was induced. Similarly, INKA2 was induced in a p53-dependent manner at both the mRNA and protein level in human cells treated with adriamycin. Reporter assays confirmed that p53 directly regulated INKA2 through an intronic binding site. The overexpression of INKA2 produced a slight decrease in cancer cell growth in the colony formation assay. Moreover, the analysis of The Cancer Genome Atlas (TCGA) data revealed a decreased INKA2 expression in tumour samples carrying p53 mutations compared with p53 wild-type samples. In addition, significantly higher levels of DNA methylation were observed in the INKA2 promoter in tumour samples, concordant with the reduced INKA2 expression in tumour tissues. These results demonstrate the potential of INKA2 as a cancer cell growth inhibitor. Furthermore, INKA2 protein interacts with the serine/threonine-protein kinase, p21 (RAC1) activated kinase (PAK)4, which phosphorylates β-catenin to prevent ubiquitin-proteasomal degradation. As β-catenin was downregulated in a stable INKA2-expressing cell line, the findings of this study suggest that INKA2 is a novel, direct downstream target of p53 that potentially decreases cell growth by inhibiting the PAK4-β-catenin pathway.

Identification of a novel p53 target, COL17A1, that inhibits breast cancer cell migration and invasion

p53 mutation is a marker of poor prognosis in breast cancers. To identify downstream targets of p53, we screened two transcriptome datasets, including cDNA microarrays of MCF10A breast epithelial cells with wild-type p53 or p53-null background, and RNA sequence analysis of breast invasive carcinoma. Here, we unveil ten novel p53 target candidates that are up-regulated after the induction of p53 in wild-type cells. Their expressions are also high in breast invasive carcinoma tissues with wild-type p53. The GO analysis identified epidermis development and ectoderm development, which COL17A1 participates, as significantly up-regulated by wild-type p53. The COL17A1 expressions increased in a p53-dependent manner in human breast cells and mouse mammary tissues. Reporter assay and ChIP assay identified intronic p53-binding sequences in the COL17A1 gene. The MDA-MB-231 cells that genetically over-express COL17A1 gene product exhibited reduced migration and invasion in vitro. Similarly, COL17A1 expression was decreased in metastatic tumors compared to primary tumors and normal tissues, even from the same patients. Moreover, high COL17A1 expression was associated with longer survival of patients with invasive breast carcinoma. In conclusion, we revealed that COL17A1 is a novel p53 transcriptional target in breast tissues that inhibits cell migration and invasion and is associated with better prognosis.