Project Details
Projekt
Signal integration by phosphorylation and complex formation of Bim and Puma
Applicant
Professor Dr. Christoph Borner
Subject Area
Pharmacology
Cell Biology
Cell Biology
Term
from 2014 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 232935877
Puma is a BH3-only protein of the Bcl-2 family required for various types of apoptosis scenarios. This does not only involve genotoxic stress where Puma is transcriptionally induced by p53 but also apoptosis induced by growth factor or cytokine deprivation, virus infection or other cell damaging agents such as for example protein kinase inhibition. Dysregulation of Puma may therefore have adverse consequences in many pathological situations such as cancer, degenerative diseases or immunological disorders. It was suggested that once Puma is transcriptionally induced by p53, it either directly activates Bax/Bak to trigger mitochondrial outer membrane permeabilization (MOMP) and subsequent cytochrome c release and caspase activation or it binds to Bcl-2-like survival factors to release Bax/Bak for autoactivation. It however turns out that this might be a rather special situation. In most cells, Puma is already expressed at appreciable levels and binds to Bcl-2 like survival factors so that it is prevented from incidentally activating Bax/Bak. Moreover, it forms high molecular mass complexes in healthy cells, which exceed in size of dimers with Bcl-2 survival factors. The composition of these protein complexes and their role in Puma inactivation has remained enigmatic. It is also not known how Puma can be activated from such complexes, whether this involves posttranslational modifications, the binding of other proteins and/or the release of Puma to become free for Bax/Bak activation. Lastly, although it has been suggested that Puma levels are low in healthy cells due to proteasomal degradation, the exact molecular mechanism of this degradation has not yet been revealed. In this proposal we want to address these remaining questions by identifying the binding partners, posttranslational modifications and degradation mechanisms of Puma in healthy and apoptotic cells and decipher their functions for the pro-apoptotic activity of this BH3-only protein. In addition, we will use a particular cellular system (IL-3 dependent monocytes) and genetic, biochemical and systems biology approaches to identify the sequential steps of how Puma interacts with Bcl-2 survival factors or Bax/Bak and cooperates with other BH3-only proteins such as Bim and Bad to trigger MOMP. Our findings will improve our understanding about how Puma functions on the molecular level and how Bax/Bak-mediated MOMP is coordinated by the interplay of several Bcl-2 survival factors and BH3-only proteins.
DFG Programme
Research Units
