New machinery of cancer cell immune response discovered by Xuerui Yang’s group: dsRNA-induced interferon response in breast cancer cells due to aberrant RNA splicing upon reduction of HNRNPC

2018-09-04 22:56:39

Host innate immune response in tumor cells plays a critical role in cancer development and is one of the determining factors for the sensitivity and resistance to cancer immunotherapy. Biogenesis of the immunostimulatory factors in cancer cells and their molecular machineries in triggering immune responses are of particular interest in the field of cancer immunology. Dr. Xuerui Yang’s group in the School of Life Sciences at Tsinghua University has discovered a new path from aberrant RNA splicing to activation of interferon production and down-stream immune response in breast cancer cells MCF7 and T47D. The team showed that reduction of an RNA binding protein (RBP) HNRNPC, which was best known for its critical role in maintaining normal RNA splicing, resulted in accumulation of double-stranded RNA (dsRNA) and activation of a cascade of interferon responses in tumor cells, which eventually arrested cell proliferation and tumor growth. This work has been recently published in The EMBO Journal (Title: Function of HNRNPC in breast cancer cells by controlling the dsRNA-induced interferon response. Link: http://dx.doi.org/10.15252/embj.201899017).

Elevated expression of HNRNPC has been reported in cancer cells, while the essentialness and functions of HNRNPC in tumors were not clear. A research team in Dr. Xuerui Yang’s lab, including 3 PhD students Yusheng Wu, Wenwei Zhao, Yang Liu, and other researchers, found that repression of HNRNPC in the breast cancer cells MCF7 and T47D inhibited cell proliferation and tumor growth. Their computational inference of the key pathways and experimental investigations revealed that the cascade of interferon responses was responsible for such tumor-inhibitory effect.

Interferon production and the down-stream immune response can be triggered by invasion of microbes such as virus and bacteria or by endogenous DNA or RNA under special conditions such as cancer. Several recent studies have reported that up-regulated dsRNA from endogenous retrovirus (ERV) in tumor cells, triggered by DNA methyltransferase inhibitors or CDK4/6 inhibitors, induced IFN responses and thus inhibited tumor development (Chiappinelli, Cell 2015; Goel, Nature 2017; Roulois, Cell 2015). Interestingly, Dr. Yang’s group found that the strong interferon response upon repression of HNRNPC was also triggered by endogenous dsRNA species, which to their surprises have nothing to do with the previously reported ERV sequences. Instead, these dsRNAs were highly enriched by Alu sequences and mostly originated from pre-mRNA introns.

Staining of endogenous dsRNA (left) and quantification of dsRNA increase (right) upon silencing of HNRNPC

Alu sequences are highly abundant in human genome. HNRNPC is critical for exclusion of the introns with Alu during RNA splicing. Dr. Yang’s team proved that dysregulated pre-mRNA splicing due to reduction of HNRNPC triggered non-sense mediated decay, as the aberrant mRNA products cannot be translated as normal. Decay of these aberrant mRNA molecules led to an unexpected consequence, i.e., accumulation of Alu dsRNAs. This is because the Alu sequences of the mRNAs commonly form dsRNA structures, which are more resistant to RNA decay than the other parts of the mRNA molecules. Accumulation of these immunostimulatory dsRNAs eventually triggered interferon responses in the tumor cells.

In summary, this study established a new machinery for activation of the immune response in breast cancer cells MCF7 and T47D. Such machinery connects RNA splicing regulated by an individual RBP to the immune responses of tumor cells via dysregulated endogenous RNA processing in cancer. The results inspire more intriguing questions in the field of cancer immunology, to which Dr. Xuerui Yang’s group will be pursuing in their future work.

Molecular machinery discovered in this research work.

PhD students Yusheng Wu, Wenwei Zhao, and Yang Liu in Xuerui Yang’s lab are the co-first authors of the paper. The study was financially supported by the national key research and development program, Precision Medicine Project, the National Natural Science Foundation of China, the Tsinghua University Initiative Scientific Research Program, the Tsinghua–Peking Joint Center for Life Sciences.The study also received supports from the core facilities of Genome Sequencing, High-Performance Computing, shRNA Library, and Cell Imaging & Function of the National Protein Science Facility (Beijing), and the Lab Animal Center at Tsinghua University.

References

Chiappinelli, K.B., Strissel, P.L., Desrichard, A., Li, H., Henke, C., Akman, B., Hein, A., Rote, N.S., Cope, L.M., Snyder, A., et al. (2015). Inhibiting DNA Methylation Causes an Interferon Response in Cancer via dsRNA Including Endogenous Retroviruses. Cell 162, 974-986.

Goel, S., DeCristo, M.J., Watt, A.C., BrinJones, H., Sceneay, J., Li, B.B., Khan, N., Ubellacker, J.M., Xie, S., Metzger-Filho, O., et al. (2017). CDK4/6 inhibition triggers anti-tumour immunity. Nature 548, 471-475.

Roulois, D., Loo Yau, H., Singhania, R., Wang, Y., Danesh, A., Shen, S.Y., Han, H., Liang, G., Jones, P.A., Pugh, T.J., et al. (2015). DNA-Demethylating Agents Target Colorectal Cancer Cells by Inducing Viral Mimicry by Endogenous Transcripts. Cell 162, 961-973.