Purpose: In our previous study, we identified that lncRNA ILF3 antisense RNA 1 (ILF3-AS1) is increased and has oncogenic roles in melanoma. However, the cause of the upregulation of ILF3-AS1 and the modulation between ILF3-AS1 and ILF3 in melanoma are still unknown. This study aimed to investigate the significances of the interaction between ILF3-AS1 and ILF3 in melanoma.
Materials and methods: The expression of ILF3 in melanoma tissues and cell lines was measured by quantitative real-time PCR (qRT-PCR). The interactions between ILF3-AS1 and ILF3 were explored by the RNA immunoprecipitation assay, the transcription inhibition assay, qRT-PCR, the chromatin immunoprecipitation assay, and Western blot. Gain-of-function and loss-of-function assays were performed to investigate the effects of ILF3 and ILF3-AS1 on melanoma proliferation, migration, and invasion.
Results: ILF3 is also increased in melanoma tissues and cell lines. Increased expression of ILF3 predicts poor survival of melanoma patients. Mechanistic investigation revealed that ILF3 directly binds ILF3-AS1, increases ILF3-AS1 transcript stability, and upregulates ILF3-AS1 transcript levels. ILF3-AS1 represses the binding of EZH2 to the promoter of ILF3 , induces euchromatin formation at ILF3  promoter, and activates ILF3  transcription. Thus, ILF3 and ILF3-AS1 form positive feedback loop, which induces the upregulation of ILF3 and ILF3-AS1 in melanoma. The expression of ILF3-AS1 is positively correlated with ILF3 in melanoma tissues. Functional assays revealed that overexpression of ILF3 promotes melanoma proliferation, migration, and invasion. Depletion of ILF3 inhibits melanoma proliferation, migration, and invasion. Moreover, concurrent depletion of ILF3 and ILF3-AS1 significantly suppresses melanoma proliferation, migration, and invasion.
Conclusion: Both ILF3-AS1 and ILF3 are increased in melanoma. ILF3-AS1 and ILF3 positively regulate each other. Concurrent targeting ILF3-AS1 and ILF3 has significant tumor-suppressive roles in melanoma. Our data suggested that targeting the positive feedback loop between ILF3 and ILF3-AS1 may be promising therapeutic strategies for melanoma.
Keywords: lncRNA, ILF3-AS1, feedback loop, ILF3, melanoma, progression