Abstract 469: PIWI-interacting RNA 50485 (piRNA-50485) is a novel lung tumor suppressor

Abstract Introduction: It is crucial to identify new driver genes and associated downstream pathways to facilitate the development of targeted therapies to effectively treat late-stage and metastatic lung cancer. One pathway involves the Ras association domain family 1 (RASSF1) gene which encodes multiple isoforms. Our laboratory has discovered that the RASSF1C isoform exhibits functional characteristics of an oncogene. We discovered that RASSF1C modulates the expression of PIWI-(Drosophila)-like 1 (PIWIL1, a stem cell renewal gene), as well as novel PIWI-interacting RNAs (piRNAs), which are regulators of the stem cell phenotype and have been linked to oncogenesis. While studying this pathway, we have identified novel piRNAs that are modulated by RASSF1C in non-small cell lung cancer (NSCLC) cells that appear to act as oncogenes or tumor suppressors. Methods: We conducted a global microarray screen to identify RASSF1C PIWI-interacting RNA (piRNA) gene targets. Several piRNA genes that are up- and down-regulated by RASSF1C were identified and the expression of selected up-regulated and down-regulated target genes were confirmed by RT-PCR. We evaluated the impact of selected piRNAs on lung cancer cell proliferation and migration in vitro. We also assessed the expression of the validated piRNA target genes in lung tumor and matched normal tissues. Host and target genes for specific piRNAs were identified using a piRNA database (piRNAdb.org). Results: Among the down-regulated piRNAs, we found that restoring piR-50485 expression drastically decreased lung cancer cell proliferation and invasion, suggesting that piR-50485 could be a potent inhibitor of lung cancer cell growth and progression. Consistent with this, we found that piR-50485 expression is significantly down-regulated in about 60% of human lung cancers. We also identified that the ZHX3 gene (a transcription repressor), which is down-regulated in human lung cancers, is the host gene for piR-50485. In addition, we identified the ZNF618 gene (a transcription co-regulator) that is up-regulated in lung tumor tissue, is a piR-50485 target gene. Consistent with this, treatment of lung cancer cells with piR-50485 mimics resulted in a significant decrease of ZNF618 protein levels, cell proliferation, and migration. Further, increased expression levels of ZHX3 are associated with higher lung cancer patient survival, while increased ZNF618 levels are associated with lower survival. Our novel findings suggest the hypothesis that the piR-50485-ZHX3-ZNF618 gene axis could negatively impact lung cancer cell growth and progression. Conclusion: Exploring the impact of the piR-50485-ZHX3-ZNF618 gene axis on lung cancer growth is a novel concept about which nothing is currently known. We are studying piR-50485 to determine if it can be an effective therapy for lung cancer metastasis, and whether it provides important prognostic information about lung cancer outcomes. Citation Format: Mark E. Reeves, Yousef G. Amaar. PIWI-interacting RNA 50485 (piRNA-50485) is a novel lung tumor suppressor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 469.