Study On The Roles Of LncRNAs Transcribed From Sex Chromosome In HCC Gender Disparity

Primary liver cancer is one of the most common cancers worldwide, especially in Eastern Asia areas. Despite various treatments, HCC results in a very high death rate, ranking as the second leading cause of cancer death in men and sixth in women. Approximate 80% of primary liver cancers are hepatocellular carcinoma(HCC). Risk factors for HCC include chronic hepatitis virus infection, chemical toxins, alcoholic cirrhosis and non-alcoholic cirrhosis, type II diabetes and smoking. A key phenomenon of HCC is that males are more susceptible than females. Sex hormones and cytokines are thought to contribute greatly to this gender disparity. However, sex hormone therapy and castration treatment for HCC did not achieve ideal effects, causing severe adverse effects. As a result, the exact reasons deeprooted in the gender differences deserve for further investigation.Difference of sex chromosomes is the biggest genetic difference between men and women(XX & XY). However, studies of sex chromosome coding genes also failed to reveal the reasons of the HCC gender difference. Long non-coding RNA is a kind of transcripts longer than 200 nucleotides without protein coding ability, and is involved in a variety of physiological and pathological process in the form of RNA. In this study, investigated roles of lncRNAs transcribed from sex chromosomes in HCC. One X chromosome in somatic cells of females is inactivated to balance gene dosage between the sexes, namely X chromosome inactivation(XCI). However, recent studied showed that some genes escape from XCI, resulting in imbalance again. We investigated whether the escaping genes escape from the silence in female livers and whether they protect females from HCC. The Y chromosome is a male specific chromosome, especially the male specific region(MSY), which encodes the male specific genes. We aim to discover whether Y chromosome specific genes are actvated in male liver and act as oncogens in male HCC.Through screening, lnc-FTX was found to be expressed at higher levels in female livers than in male livers and to be significantly downregulated in HCC tissues compared with normal liver tissues. Patients with higher lnc-FTX expression exhibited longer survival, suggesting that lnc-FTX is a useful prognostic factor for HCC patients. lnc-FTX inhibits HCC cell growth and metastasis both in vitro and in vivo. lnc-FTX interference in QSG 7701 hepatocytes promoted subcutaneous tumor formation in nude mice. RNA pull-down and RNA immunoprecipitation(RIP) assays demonstrated that lnc-FTX binds to MCM2 and hinders MCM2 loading onto chromosome and formation of DNA replication complex, thus inhibiting DNA replication and cell proliferation. lnc-FTX sequesters mi R-374 a and blocks mi R-374 a function through complementary base pairing, demonstrated by RNA pull-down, MS2-RIP, and luciferase report system assays. lnc-FTX upregulates miR-374 a target genes, WIF1, PTEN, and WNT5 A, negative Wnt regulators, through decreasing free miR-374 a. TOP/FOPflash assay and changes of Wnt activated genes confirmed decrease of Wnt signal activity by lnc-FTX. As a result, lnc-FTX inhibits HCC cell EMT and migration. Moreover, localization may decide the lnc-FTX binding partner. In the cytoplasm, lnc-FTX sequesters mi R-374 a and blocks miR-374 a function due to complementary base pairing; in the nucleus, lnc-FTX binds MCM2 and prevents its loading onto chromosomes. In conclusion, lnc-FTX acts as a protective factor in female liver. With higher expression in female livers, lnc-FTX may inhibit HCC initiation by repressing the proliferation of aberrant hepatocytes and contribute to female resistance to hepatocellular carcinogenesis. After HCC initiation, higher levels of lnc-FTX recruit mi R-374 a and inhibit HCC invasion and metastasis, retarding HCC progression.Through screening of Y chromosome transcriptions in HCC and adjacent liver tissues, we discovered a long non-coding RNA RBMY2FP(RNA binding motif protein, Y-linked, family 2, member F pseudogene) that is specifically expressed in about 1/3 male HCC tissues, with no expression in adjacent livers. Nor is lnc-FTX expressed in lung cancer, colon cancer, pancreatic cancer or esophageal cancer tissues. Positive expression of lnc-RBMY2 FP in male HCC is related to poor patient survival. lnc-RBMY2 FP enhances HCC cell growth, proliferation and stemness both in vitro and in vivo. Mechanistically, lnc-RBMY2 FP interacts with DNMT1 and hampers its binding onto promoters of RBMY family. Thus, maintenance of promoter methylation status is disturbed because of inhibition of DNMT1 activity, leading to increased expression RBMY1A1 protein and enhanced hepatocarcinogenesis.In conclusion, we elucidated important roles of sex chromosome transcribed lncRNAs in HCC. We find that tumor repressor lnc-FTX facilitates female resistance to HCC and carcinogenic factor lnv-RBMY2 FP makes males susceptible to HCC. These findings may partially explain the male preference of HCC and potentially contribute to HCC prevention and treatment.