Abstract 5304: Gem-interacting protein (Gmip) is potentially a new lung tumor suppressor
Authors: Amaar Yousef G. , Reeves Mark E. 
Published: August 2019

Introduction: We have identified a novel RASSF1C-PIWIL1-piRNA pathway that appears to promote lung cell proliferation and migration. PIWI-like proteins interact with PIWI interacting RNAs (piRNAs) to form complexes that regulate gene expression at the transcriptional and post-transcriptional levels leading to stimulation of stem cell renewal and proliferation. We previously have shown that RASSF1C regulates the expression of the PIWIL1-piRNA gene axis, suggesting the hypothesis that the RASSF1C-PIWI-piRNA pathway may promote lung cancer stem cell development and progression, in part, by epigenetically modulating the expression of growth promoting and growth inhibiting genes. To validate this hypothesis, we used a non-small cell lung cancer cell model to identify candidate genes targeted by the RASSF1C-PIWIL1-piRNA pathway through a gene methylation mechanism.

Methods: We have previously conducted a study to assess the impact of over-expressing RASSF1C and knocking down RASSF1C and P1WIL1 expression on global gene DNA methylation in the NSCLC cell line H1299 using the Reduced Representation Bisulfite Sequencing method. Candidate Differentially Methylated Regions (DMR) were identified by comparing DNA methylation profiles of experimental and control cells. Statistically significant candidate genes residing in hypo- and hyper-methylated regions in lung cancer cells were identified.

Results: We found that over-expression of RASSF1C and knocking down RASSF1C and PIWIL1 modulated DNA methylation of genomic regions. Among the candidate target genes identified is Gmip, a RhoA-specific GTPase-activating protein. We found over-expression of RASSF1C increases and knock-down of RASSF1C or PIWIL1 decreases intragenic methylation of Gmip. Consistent with this, RT-PCR analysis shows that Gmip mRNA levels are reduced in lung cancer cells over-expressing RASSF1C while Gmip mRNA levels are increased in cells with RASSF1C or PIWIL1 knocked down. Further, Kaplan-Meier analysis of survival of lung adenocarcinoma patients in The Cancer Genome Atlas shows that high expression of Gmip is associated with significantly higher patient survival, suggesting that Gmip may function as a tumor suppressor.

Conclusion: The RASSF1C-PIWI-piRNA pathway may drive epigenome regulation and genesis of lung cancer stem cells through modulation of novel genes such as Gmip. Interestingly, Gmip is among 3781 mRNAs that are predicted to be targeted by the PIWIL1-piRNA complex in mouse male germ cells. Our findings are the first to suggest that Gmip is a human lung tumor suppressor. Since virtually nothing is known about Gmip function in human cancer, its function as a tumor suppressor in lung cancer needs to be studied and characterized.

Citation Format: Yousef G. Amaar, Mark E. Reeves. Gem-interacting protein (Gmip) is potentially a new lung tumor suppressor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5304.