The Role of Methylation in the CpG Island of the ARHI Promoter Region in Cancers

Hypermethylation can downregulate many tumor suppressor gene expressions. Aplasia Ras homologue member I (ARHI, DIRAS3) is one of the maternally imprinted tumor suppressors in the RAS superfamily. This chapter overviewed the importance of ARHI methylation and expression phenomes in various types of cancers, although the exact mechanisms remain unclear. As an imprinted gene, aberrant DNA methylation of the paternal allele of ARHI was identified as a primary inhibitor of ARHI expression. The role of methylation in the CpG islands of the ARHI promoter region vary among ovarian cancers, breast cancers, hepatocellular carcinoma, colon cancers, pancreatic cancer osteosarcoma, glial tumors, follicular thyroid carcinoma, or lung cancers. The methylation of ARHI provides a new insight to understand molecular mechanisms of tumorigenesis and progression of cancers.

The mechanisms of DIRAS family members in role of tumor suppressor

DIRAS family is a group of GTPases belonging to the RAS superfamily and shares homology with the pro-oncogenic Ras GTPases. Currently, accumulating evidence show that DIRAS family members could be identified as putative tumor suppressors in various cancers. The either lost or reduced expression of DIRAS proteins play an important role in cancer development, including cell growth, migration, apoptosis, autophagic cell death, and tumor dormancy. This review focuses on the latest research regarding the roles and mechanisms of the DIRAS family members in regulating Ras function, cancer development, assessing potential challenges, and providing insights into the possibility of targeting them for therapeutic use.

The expression of aplysia ras homolog I (ARHI) and its inhibitory effect on cell biological behavior in esophageal squamous cell carcinoma

Background

Aplysia ras homolog I (ARHI) is a Ras-related maternally imprinted tumor suppressor gene. Loss of ARHI expression contributes to the malignant progression of various tumors. However, reports on the clinical implications and functional role of ARHI expression in esophageal squamous cell carcinoma (ESCC) are limited. This study examined the role of ARHI in ESCC.

Methods

In total, 81 patients diagnosed with ESCC based on histopathological evaluations who were subjected to surgical resection were included in the study. ARHI expression was analyzed by immunohistochemistry and western blotting, examining the correlations between ARHI expression and patient clinicopathological features. The functional effects of ARHI overexpression were examined using a Cell Counting Kit-8 assay, flow cytometry, a Transwell assay, wound healing, and western blotting in the ECA109 cell line.

Results

ARHI was highly expressed in 27.5% (22/81) of ESCC specimens (adjacent noncancerous tissues, 85.2%, 69/81; P<0.05). The ARHI expression level was significantly lower in patients with lymph node metastasis than in patients without (P<0.05). A Kaplan–Meier survival analysis showed that patients with low ARHI expression had shorter survival than patients with high expression (P<0.05), and a multivariate Cox analysis revealed that ARHI is an independent predictor of overall survival (P=0.029). Finally, overexpression of ARHI in ESCC cells indicates that ARHI suppresses proliferative capacity, invasive capacity, and cell cycle progression and may also suppress epithelial–mesenchymal transition and induce apoptosis and autophagy.

Conclusion

ARHI may be a prognostic biomarker and a potential therapeutic target in ESCC.

ARHI overexpression induces epithelial ovarian cancer cell apoptosis and excessive autophagy

OBJECTIVE

ARHI is a maternally imprinted tumor suppressor gene that is responsible for initiating programmed cell death and inhibiting cancer cell growth. However, the influence of ARHI on epithelial ovarian cancer cell death and the underlying mechanisms behind how ARHI regulates cancer cells still require further studies.

METHODS

Epithelial ovarian cancer cells TOV112D and ES-2 were used in this in vitro study. Cell proliferation, apoptosis, and autophagy activities were compared in TOV112D and ES-2 cells transfected with ARHI vectors or control vectors. Bcl-2 siRNA was transfected into TOV112D cells to investigate the roles of Bcl-2 played in regulating apoptosis and autophagy.

RESULTS

ARHI expression was reduced in TOV112D and ES-2 cells compared with normal epithelial ovarian cells (NOE095 and HOSEpiC). Overexpressed ARHI inhibited cancer cell proliferation, whereas induced forced cell apoptosis and excessive formation of autophagosomes inhibited promoted cell death. Furthermore, we found that Bcl-2 expression moderately declined in response to ARHI overexpressing in ES-2 and TOV112D cells; meanwhile, more apoptotic cells and higher LC3 level presented after silence of Bcl-2 in TOV112D cells. Reduced Bcl-2-Beclin 1 complex were observed in ARHI overexpressing cells. Moreover, modulation of ARHI to Bcl-2 expression could be ascribed partially to the activation of PI3k/AKT pathway. The addition of LY294002 enabled to suppress Bcl-2 expression and cell proliferation.

CONCLUSIONS

The silence of ARHI expression in vitro seems to accelerate the malignant transformation of healthy ovarian cells by restraining apoptosis and autophagy. The overexpressed ARHI in TOV112D cancer cells suppresses the activation of PI3K/AKT and reduces the expression of Bcl-2, leading to enhanced cell apoptosis and autophagic cancer cell death.

Effects of ARHI on breast cancer cell biological behavior regulated by microRNA-221

The aplysia ras homolog member I (ARHI) is a tumor suppressor gene and is downregulated in various cancers. The downregulation of ARHI was regulated by miR-221 in prostate cancer cell lines. However, it has not been reported whether ARHI is regulated by miR-221 in breast cancer. Here, we reported that the ARHI protein level was downregulated in breast cancer tissues and breast cancer cell lines. The overexpression of ARHI could inhibit cell proliferation and invasion and induce cell apoptosis. To address whether ARHI is regulated by miR-221 in breast cancer cell lines, the results in this study showed that a significant inverse correlation existed between ARHI and miR-221. MiR-221 displayed an upregulation in breast cancer tissues and breast cancer cell lines. The inhibition of miR-221 induced a significant upregulation of ARHI in MCF-7 cells. To prove a direct interaction between miR-221 and ARHI mRNA, ARHI 3'UTR, which includes the potential target site for miR-221, was cloned downstream of the luciferase reporter gene of the pMIR-REPORT vector to generate the pMIR-ARHI-3'UTR vector. The results confirmed a direct interaction of miR-221 with a target site on the 3'UTR of ARHI. In conclusion, ARHI is a tumor suppressor gene that is downregulated in breast cancer. The overexpression of ARHI could inhibit breast cancer cell proliferation and invasion and induce cell apoptosis. This study demonstrated for the first time that the downregulation of ARHI in breast cancer cells could be regulated by miR-221.