Co-regulation and function of FOXM1/RHNO1 bidirectional genes in cancer

The FOXM1 transcription factor is an oncoprotein and a top biomarker of poor prognosis in human cancer. Overexpression and activation of FOXM1 is frequent in high-grade serous carcinoma (HGSC), the most common and lethal form of human ovarian cancer, and is linked to copy number gains at chromosome 12p13.33. We show that FOXM1 is co-amplified and co-expressed with RHNO1, a gene involved in the ATR-Chk1 signaling pathway that functions in the DNA replication stress response. We demonstrate that FOXM1 and RHNO1 are head-to-head (i.e., bidirectional) genes (BDG) regulated by a bidirectional promoter (BDP) (named F/R-BDP). FOXM1 and RHNO1 each promote oncogenic phenotypes in HGSC cells, including clonogenic growth, DNA homologous recombination repair, and poly-ADP ribosylase inhibitor resistance. FOXM1 and RHNO1 are one of the first examples of oncogenic BDG, and therapeutic targeting of FOXM1/RHNO1 BDG is a potential therapeutic approach for ovarian and other cancers.

[RHNO1: A novel noncoding RNA highly expressed in the testis and involved in DNA double-strand break repair]

OBJECTIVE

To investigate the role of a long noncoding RNA (lncRNA) transcribed from the RHNO1 gene we newly identified in DNA double-strand break (DSB) repair.

METHODS

The transcription and translation of the RHNO1 gene were validated by Western blot, real-time PCR and liquid chromatography-tandem mass spectrometry (LC-MS/MS) based on the overexpressed RHNO1 plasmid. The transcription level of RHNO1 in the mouse tissue was detected by real-time PCR and its expression in the spermatogenic cycle determined by in situ hybridization. The role of RHNO1 in the DNA DSB repair was further verified using the DSB model established by exposing the germ cells to ultraviolent radiation.

RESULTS

The full-length RHNO1 gene could be transcribed as a novel lncRNA in vitro, highly expressed in the mouse testis tissue, and mainly located in spermatocytes and round spermatids. RHNO1 was involved in DNA DSB repair in the spermatogenic cells.

CONCLUSIONS

We identified a novel lncRNA, RHNO1, which is highly expressed in the mouse testis and participates in DNA damage repair in the germ cell line.