PIWI-like protein, HIWI2 is aberrantly expressed in retinoblastoma cells and affects cell-cycle potentially through OTX2

Suganya Sivagurunathan,Jayamuruga Pandian Arunachalam,Subbulakshmi Chidambaram

doi:10.1186/s11658-017-0048-y

Abstract

Retinoblastoma (RB), a childhood cancer, is caused by biallelic mutation of the RB1 gene, but its development is not clearly understood. Furthermore, the presence of a cancer stem cell subpopulation in RB might impact its treatment. PIWI protein, known for its role in stem cell self-renewal, is aberrantly expressed in cancers. We examined the role of the PIWI-like protein HIWI2 in RB and its effect on the stem cell markers in cells of the RB line, Y79. The expression of HIWI2 is significantly increased in Y79 compared with its level in HeLa and ARPE19 cells. The stem cell markers Oct-3/4, Nanog and Sox-2 were not altered upon HIWI2 knockdown in Y79 cells. Interestingly, OTX2 was significantly downregulated in the absence of HIWI2. Otx2 transcripts also decreased in HIWI2-silenced Y79 and ARPE19 cells. Moreover, silencing HIWI2 in Y79 accumulated the cells at G2–M phase and reduced the levels of proliferating cell nuclear antigen (PCNA) and the tumor suppressor, p16. Our results demonstrate that HIWI2 is aberrantly expressed in Y79 cells and silencing of HIWI2 downregulates OTX2, suggesting that HIWI2 might play a role in the progression of RB.

Highlights

Retinoblastoma (RB), the most common ocular cancer, mainly occurs due to the biallelic mutation of the RB1 gene on chromosome 13 [1]
The expression of HIWI2 is elevated in Y79 cells The expression of the HIWI2 transcript was studied using quantitative PCR in human retinal pigment epithelial cells (ARPE19), human cervical epithelial carcinoma cells (HeLa) and human RB cells (Y79)
Western blot analysis showed that HIWI2 expression was 4-fold higher in HeLa than in Adult retinal pigment epithelial cells (ARPE19) (Fig. 1c) and there was 5.9-fold increase in HIWI2 expression in Y79 over HeLa (Fig. 1d)

Summary

Introduction

Retinoblastoma (RB), the most common ocular cancer, mainly occurs due to the biallelic mutation of the RB1 gene on chromosome 13 [1]. The “two-hit” hypothesis suggests that two mutational events are needed in RB1 for RB to develop [2]. Besides the inactivation of RB1, epigenetic changes are involved in the tumor formation [3, 4]. Because many factors are involved in its development, RB treatment is challenging. Brachytheraphy and laser photocoagulation have devastating effects [5], so better therapies with less disease morbidity are essential.

Results

Discussion

Conclusion