CHAPTER 5 KTN 1-AS 1 , an important downstream effector of Myc , controls B-cell lymphoma proliferation

Myc is an important transcription factor with oncogenic properties in many types of cancer, including Burkitt lymphoma (BL). As Myc itself is considered undruggable, downstream targets need to be identified to allow development of novel therapeutic approaches. Recently, long noncoding (lnc)RNAs were described to be important downstream genes of Myc in several types of cancer. To identify high-confidence Mycregulated lncRNAs in B-cell lymphoma we generated and overlapped diverse data sets including transcript level changes upon MYC knockdown in BL, transcripts with an early response to Myc activation in P493-6 B cells and transcripts with a Myc binding site in close vicinity to its transcription start site. This resulted in the identification of 2 Myc-induced and 4 Myc-repressed lncRNAs. In-depth characterization of the Mycinduced KTN1-AS1 lncRNA revealed severely impaired BL cell growth without increasing the rate of apoptosis upon shRNA-mediated knockdown. KTN1-AS1 was enriched in the chromatin fraction, but showed no cis-regulatory effect on the nearby proteincoding gene KTN1. Genome wide expression analysis upon KTN1-AS1 knockdown indicated potent effects on the transcription levels of 295 genes. Intriguingly, gene set enrichment analysis showed enrichment of Myc-regulated gene sets and gene sets related to metabolism. Moreover, the KTN1-AS1 regulated genes were also enriched for Myc binding sites. A possible direct interaction between Myc and KTN1AS1 was supported based on reduced Myc transcript and protein levels upon KTN1AS1 knockdown. In conclusion, we identified MYC-induced KTN1-AS1 as an important oncogenic lncRNA involved in the pathogenesis of BL by reinforcing high Myc levels via a positive feedback loop. Our data depict targeting of KTN1-AS1 as a potential novel therapeutic approach. MYC-INDUCED LNCRNA KTN1-AS1 IS AN IMPORTANT PLAYER IN THE MYC PATHWAY 99