LncRNA BC promotes lung adenocarcinoma progression by modulating IMPAD1 alternative splicing.

BACKGROUND: The therapeutic value of targeted therapies in patients with lung cancer is reduced when tumours acquire secondary resistance after an initial period of successful treatment. However, the molecular events behind the resistance to targeted therapies in lung cancer remain largely unknown. AIMS: To discover the important role and mechanism of lncRNA BC in promoting tumor metastasis and influencing clinical prognosis of LUAD. MATERIALS & METHODS: Microarrays were used to screen a comprehensive set of lncRNAs with differential expression profiles in lung cancer cells. The functional role and mechanism of lncRNA were further investigated by gain- and loss-of-function assays. RNA pull-down, protein assays, and mass spectrometry were used to identify proteins that interacted with lncRNA. TaqMan PCR was used to measure lncRNA in lung adenocarcinoma and adjacent nontumor tissues from 428 patients. The clinical significance of lncRNA identified was statistically confirmed in this cohort of patients. RESULTS: In this study, we show that the long non-coding RNA BC009639 (BC) is involved in acquired resistance to EGFR-targeted therapies. Among the 235 long non-coding RNAs that were differentially expressed in lung cancer cell lines, with different metastatic potentials, BC promoted growth, invasion, metastasis, and resistance to EGFR-tyrosine kinase inhibitors (EGFR-TKIs), both in vitro and in vivo. BC was highly expressed in 428 patients with lung adenocarcinoma (LUAD) and high BC expression correlated with reduced efficacy of EGFR-TKI therapy. To uncover the molecular mechanism of BC-mediated EGFR-TKI resistance in lung cancer, we screened and identified nucleolin and hnRNPK that interact with BC. BC formed the splicing complex with nucleolin and hnRNPK to facilitate the production of a non-protein-coding inositol monophosphatase domain containing 1 (IMPAD1) splice variant, instead of the protein-coding variant. The BC-mediated alternative splicing (AS) of IMPAD1 resulted in the induction of the epithelial-mesenchymal transition and resistance to EGFR-TKI in lung cancer. High BC expression correlated with clinical progress and poor survival among 402 patients with LUAD. DISSCUSSION: Through alternative splicing, BC boosted the non-coding IMPAD1-203 transcript variant while suppressing the IMPAD1-201 variant. In order to control the processing of pre-mRNA, BC not only attracted RNA binding proteins (NCL, IGF2BP1) or splicing factors (hnRNPK), but also controlled the formation of the splicing-regulator complex by creating RNA-RNA-duplexes. CONCLUSION: Our results reveal an important role for BC in mediating resistance to EGFR-targeted therapy in LUAD through IMPAD1 AS and in implication for the targeted therapy resistance.

LncRNA lncAY is upregulated by sulfatide via Myb/MEF2C acetylation to promote the tumorigenicity of hepatocellular carcinoma cells.

LncRNA (long noncoding RNA) is often dysregulated in tumors especially hepatocellular carcinoma (HCC). However, the dysregulation mechanism of lncRNAs is largely unknown. Here, we showed that lncRNA lncAY expression was stimulated in HCC by either endogenous or exogenous sulfatide. Elevated lncAY promoted HCC cell migration or angiogenesis, whereas lncAY silence suppressed HCC cell migration and proliferation. Interestingly, the activity of lncAY gene promoter was enhanced by sulfatide. Then Myb and MEF2C were identified as the transcription factors responsible for the stimulation of lncAY promoter activity and transcription by sulfatide. Both Myb and MEF2C enrichment on lncAY promoter was further confirmed, and their occupancy on lncAY promoter was strengthened by sulfatide for Myb or MEF2C was acetylated. Mutant Myb-K456A exhibited reduced acetylation and weak stimulation for lncAY transcription. However, Myb mutation K456/503A prevented Myb from acetylation induced by sulfatide. The mutant Myb K456/503A further was unable to occupy lncAY promoter and enhance lncAY transcription. In conclusion, this study demonstrated lncAY transcription was abnormally upregulated by sulfatide in HCC through Myb/MEF2C to promote HCC progression.

LncRNA AY promotes hepatocellular carcinoma metastasis by stimulating ITGAV transcription.

Rationale: Tumor metastasis is the main cause for cancer-related death. However, the driving molecules of metastasis remain largely unknown. Here, we aim to identify long non-coding RNAs (lncRNAs) critical for human hepatocellular carcinoma (HCC) metastasis. Methods: Microarrays were used to screen a comprehensive set of lncRNAs with differential expression profiles in sulfatide-treated cells. Mass spectrometry, protein arrays, and RNA pull-down experiments were used to identify proteins that interacted with lncRNA. Epigenetic analysis was used to study lncRNA-mediated regulation mechanisms. Results: We identified lncRNA AY927503 (AY) as a metastasis-associated molecule that was highly expressed in human hepatocellular carcinoma (HCC) and correlated with metastatic events and poor prognosis in patients with HCC. AY promoted HCC cell migration, stemness, 5-fluorouracil resistance, and metastasis in mice. However, knockdown of integrin αV (ITGAV) abolished AY-stimulated migration, cell viability in HCC cells or tube formation. AY strongly promoted ITGAV transcription and αVß3 expression by interacting with the ITGAV promoter specifically and stimulating its activity. AY was identified to interact with histone 1FX (H1FX), but deletion of the central domain of AY (AY∆371-522) abolished H1FX binding and ITGAV promoter stimulation. AY significantly enriched H3K4Me3 and acH3K9/14 but reduced H3K27Me3 and H1FX occupancy on the ITGAV promoter, which remodeled chromatin structures for RNA polymerase II recruitment. Knockdown of H1FX abrogated ITGAV transcription stimulated by AY. Conclusions: Our findings suggested that lncRNA AY promoted HCC metastasis via induction of chromatin modification for ITGAV transcription as a pioneer factor and was a potential molecular signature for metastasis or poor prognosis in patients with HCC.