The kinetoplastid parasites Trypanosoma brucei, Trypanosoma cruzi and Leishmania spp. affect millions of people worldwide, causing Human African Trypanosomiasis (HAT), Chagas? disease, and various forms of Leishmaniasis, respectively. Since drugs for these neglected tropical diseases are limited, often toxic and difficult to administer, and parasite resistance to existing drugs is on the rise, it is important to develop new chemo- therapeutic strategies. Our research is focused on trypanosome gene expression because the underlying mechanisms deviate substantially from those in the human host. For example, polycistronic transcription of protein coding genes and processing of pre-mRNA by spliced leader trans splicing are parasite-specific steps in mRNA synthesis and maturation. We discovered in T. brucei that the activity of the cyclin-dependent kinase (CDK) CRK9 is required for trans splicing. By generating a cell line that expresses analog-sensitive CRK9 and no wild-type enzyme, we could chemically inhibit the enzyme in specific manner in cultured cells. Surprisingly, we observed an instant splicing block after applying the inhibitor, suggesting that CRK9 carries out essential reversible phosphorylation on the RNA processing machinery. Our preliminary data indicate that one of CRK9?s substrate is the SR protein and known splicing factor TSR1, and that blocking CRK9 activity affects the assembly of the spliceosome, the large and dynamic RNA-protein complex that carries out the splicing reaction. Consequently, we will determine the mechanism of how CRK9 aids or controls the splicing process. Furthermore, CDKs represent a highly druggable enzyme class, and CRK9 forms an unusual trimeric enzyme complex with a deviant L-type cyclin and a kinetoplastid-specific protein, suggesting that CRK9 is a promising target for chemotherapeutic intervention. Therefore, we propose to characterize the enzyme complex and determine a minimal complex that is active and can be expressed recombinantly as prerequisite for future high throughput inhibitor screens. Finally, based on preliminary data, we will test the hypothesis that CRK9 is the target of the compound SCYX-7158 which is currently in clinical trials against HAT.
Trypanosomatid parasites cause devastating human diseases that affect millions of people worldwide. Drugs to treat these diseases are limited and parasite resistance to these drugs is on the rise. As our data on Trypanosoma brucei indicate, the cyclin-dependent kinase CRK9 forms a unique tripartite protein complex and has essential roles in the trypanosome-specific mode of gene expression and the completion of the cell cycle. Thus, analysis of the CRK9 enzyme architecture and of CRK9-controlled substrates, signaling pathways and mechanisms may unravel new chemotherapeutic intervention strategies.