Molecular Mechanism Of Interaction Between Gadd45a Protein And Long Non-coding RNA

Non-coding RNA was transcrpts without the ability to translate because of high density of stop codons or the lack of extensive "Open Reading Frame". Long non-coding RNAs (lncRNAs) are non-coding RNAs with a length of over 200 nucleotides. They have been shown to play a regulatory role on levels of transcription, post-transcription, translation and post - translation by interacting with proteins, DNAs and RNAs. An increasing number of studies have shown their close relationship with many diseases including cancer.Gadd45a (growth arrest and DNA damage) protein was a member of Gadd family and can be induced by a wide spectum of stress. It involved in process of cell cycle arrest, DNA repair and cell apoptosis through the interaction with many other proteins. With a low expression in many types of cancers, Gadd45a inhibited the development of cancer by inhibiting tumor growth, migration, invasion and tumor angiogenesis. Recent studies indicated that Gadd45a could also bind RNA. However, it remained unknown which RNA it could bind or what biological process they were involved together.RIP-seq (RNA immunoprecipitation sequencing) assay was used to identify RNAs bound to Gadd45a.72 lncRNAs were detected and Growth arrest-specific 5 (GAS5) was chosen for further study. GAS5 could not influence the amount and location of Gadd45a. However, by knocking-down or over-expressing Gadd45a or GAS5, combined with immunoprecipitation and sliver staining, we demonstrated that GAS5 improved the interaction between Gadd45a and heat shock protein 90 (HSP90), which competitively inhibited the binding of HSP90 with its co-chaperone CDC37. GAS5 also had an inhibitory effect on the interaction between HSP90 and CDC37 through Gadd45a. We also revealed a high expression of HSP90 in colonic carcinoma tissues, which could serve as an independent prognostic factor in colon cancer.In conclusion, we detected a series of RNAs, especially lncRNAs that bound Gadd45a in this study. Further, we demonstrated that Gadd45a could bind HSP90 with the help of GAS5, which competitively inhibited the interaction between HSP90 and its co-chaperone CDC37, disrupting tumor growth by acting as "HSP90 inhibitor".