Summary
Cells can be infected by bacteria that survive and propagate intracellularly in so-called phagosomes. Cells respond to these infections by altering their ‘cell biology’ to eliminate these infections and bacteria respond to these for their own survival. We have combined cell biology, biophysics, chemistry and microbiology to define chemical leads and targets controlling intracellular growth of a series of different pathogenic bacteria including Salmonella and M.tuberculosis. Silencing the human kinome with siRNA yielded 11 confirmed kinases controlling these infections. Pathway analyses showed that all kinases clustered in one pathway only, a pathway around PKB/Akt1. Further analysis showed that bacteria activate this pathway to promote their survival by preventing transport and fusion of phagosomes to lysosomes (Kuijl et al., Nature 2007). This involved the action of the downstream kinases as well, although the details still have to be solved. Inhibiting these kinases by chemical inhibitors or siRNA could control bacterial infection and such approaches can be useful for treatment of multi-drug resistant bacteria as are emerging at various sites world-wide.
If a kinase network around PKB/Akt1 is essential for intracellular survival, we can use intracellular infections to define phosphatases acting in the same pathway. We aim at combining chemical libraries with phosphatase inhibitors and phosphatase siRNAs to identify target-lead combinations controlling intracellular infections. Since the PKB/Akt pathway is involved in controlling apoptosis of tumor cells, such phosphatases could also be involved in controlling tumor growth or survival and will be tested for these purposes as well. How the phosphatases are controlled will be determined by isolating associated proteins and mass spectrometry. Ultimately we aim to arrive at networks with a comprehensive description of the signaling processes controlling infections and tumor survival.