Studies of Cellular Regulatory Mechanisms : from Genetic Switches to Cell Migration

Abstract: Cellular behaviour depends ultimately on the transcription of genes. If we know how transcription is controlled we have a better chance of understanding cellular processes. This thesis presents six studies, all concerning cellular regulatory mechanisms. One study is purely experimental and five are computational studies. A large part of the research concerns the Epstein-Barr virus (EBV). We investigate the latency programme switching of EBV, with an equilibrium statistical mechanics model that describes the transcription activities of two central viral promoters. We demonstrate that this system is bistable and predict promoter activities that correlate well with experimental data. Further we study the switching efficiency of one of the promoters, highlighting how competitive binding of transcription factors generates a more efficient geneticswitch. The EBV protein EBNA1 is known to affect cellular gene expression. With a dinucleotide position weight matrix we search the complete human genome for regions with multiple EBNA1 binding sites. 40 potential binding regions are identified, with several of particular interest in relation to EBV infections. The final study on EBV is purely experimental, in which we demonstrate an interaction between the Syk kinase and integrin β4. Moreover, we show how reduced levels of these proteins affect migration of epithelial LMP2a positive cells, and hypothesise that these effects are due to the Syk-β4 interaction. The two remaining studies presented in this thesis concern other cellular systems. Dynamic properties of two different regulatory feedback mechanisms for transport and metabolism of small molecules are investigated. The synergetic effect of adding a regulatory loop is exemplified with the iron metabolism in bacteria. The final project concerns the λ phage. With the equilibrium statistical mechanics method for describing promoter activities we characterise the equilibrium properties of λ mutants and compare with experimental findings. We argue that the observed differences between model and experiment are due to a larger perturbation of the genetic circuit than presumed. The research presented in this thesis shed light on the properties of several regulatory mechanisms. As computational studies they add perspective to the experimental research in this field and provide new hypothesis for further research.