Abstract 1827: HnRNP I interacts with lncRNA UCA1 and regulates its stability.

Abstract Background: The human genome also makes a large number of non-coding RNAs including long non-coding RNAs (lncRNAs) and microRNAs in addition to protein-coding genes. While microRNAs are well characterized, little is known about lncRNAs. Emerging evidence has implicated lncRNAs in gene regulation; and they are often aberrantly expressed in a variety of human diseases, in particular cancer. The heterogeneous nuclear ribonucleoprotein I (hnRNP I) is a member of the large hnRNP family and has been implicated in mRNA splicing, stability and translational regulation of certain RNA transcripts. During screening for lncRNA-interacted proteins, we identified hnRNP I as a binding partner for UCA1. However, it remains unclear how hnRNP I interacts with UCA1 and whether such an interaction impacts UCA1-mediated cell growth and responsiveness to anti-cancer drugs. Methods: To determine cell growth and response to doxorubicin, we performed MTT assays as well as cell counting assays. Protein levels from treated cells were analyzed by western blot. Real-time RT-PCR was used to determine relative expression of genes. Interaction between hnRNP I and UCA1 was confirmed by RNA co-immunoprecipitation and RNA pulldown. RNA stability was determined by treating MCF-7 cells with actinomycin D, followed by real-time RT-PCR. hnRNP I was knock down by transient transfection of hnRNP I siRNAs. Results: We found that UCA1 induced proliferation and increased resistance to doxorubicin in MCF-7 cells. RNA pulldown assays revealed that UCA1 RNA directly interacted with hnRNP I. This interaction was further confirmed by RNA immunoprecipitation by hnRNP I antibody. Real-time RT-PCR revealed that knockdown of hnRNP I by RNAi reduced the level of UCA1 in MCF-7 cells and it also repressed the induction of UCA1 by doxorubicin. Further experiments suggested that hnRNP I impacts the UCA1 stability. We showed that half-life of UCA1 was about 12 h but was decreased to about 6 h in the presence of hnRNP I siRNAs. We further showed that the phosphorylated form of hnRNA I, predominantly in the cytoplasm, was a major form that interacts with UCA1. Conclusion: Taken together, these results suggest that hnRNP I plays a role in regulation of the stability of UCA1. Since previous work implicates the involvement of UCA1 in tumor cell growth and chemoresistance, a better understanding of the underlying mechanism will provide new insight of targeting UCA1 in cancer therapy. Citation Format: Jianguo Huang, Yin-Yuan Mo. HnRNP I interacts with lncRNA UCA1 and regulates its stability. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1827. doi:10.1158/1538-7445.AM2013-1827