A-kinase anchoring proteins, or AKAPs, bind cAMP-dependent kinase (PKA) and target it to specific subcellular locations, ensuring the regulation in space and time of PKA signaling. Moreover, AKAPs organize signaling platforms containing additional signaling molecules or effectors such as protein kinases, phosphatases or phosphodiesterases, thus providing AKAPs with a pivotal role in different functions in various places of the cell. For instance, we have shown that in addition to binding PKA at the mitochondrial membrane and at the nuclear envelope/endoplasmic reticulum, AKAP149 self-associates, a condition which enables RNA binding (Rogne et al, 2006). AKAP149 also contains a conserved PP1-binding domain located within the KH domain that is responsible for RNA binding. We showed that RNA and PP1 association with AKAP149 are mutually exclusive and regulated by phosphorylation within the KH domain. Interestingly, AKAP149 mutants unable to bind RNA lead to a collapse of the mitochondrial network by a mechanism which remains unknown (Rogne et al., 2009).

Figure: Co-distribution of DMDDX28, a mitochondrial marker, and AKAP149-mCherry constructs transfected in HeLa cells.

We are now investigating a potential role for another nuclear AKAP, AKAP95, as a relay platform processing information from signaling pathways to regulators of gene expression such as transcription factors and chromatin remodeling factors, as well as the epigenetic regulation of these processes.

Persons involved: Dr. Thomas Küntziger

PNUTS (Video)

PNUTS is a nuclear PP1-targeting and regulatory subunit which we have shown is implicated in chromosome condensation and decondensation at mitosis and in a cell-free system (Landsverk et al., 2005). We have recently shown that depletion of PNUTS results in a prolonged mitotic prophase caused by a checkpoint-dependent delay at the G₂/M transition. We further show that PNUTS is an integral component of the DNA damage response and is involved in DNA repair (Landsverk et al, 2010, in press). 

Figure: siRNA-transfected Histone2B-EGFP cells in prophase. Numbers indicate min before nuclear envelope breakdown (F. Mora-Bermúdez and J. Ellenberg).

 

Persons involved: Dr. Helga B. Landsverk, Dr. Thomas Küntziger

Collaborators: Dr. Jan Ellenberg (EMBL, Heidelberg), Prof. Mathieu Bollen (Catholic University of Leuven, Belgium), Dr. Randi Syljuåsen (Rikshospital-Radium Hospital Research Centre, Oslo).

 

 

Lamin A, chromatin and laminopathies

The nuclear envelope consists of a double membrane, nuclear pores and the lamina. THe lamina is a meshwork of intermediate filaments called A- and B-type lamins. Mutations in the lamin A (LMNA) gene cause debilitating diseases, including a Dunnigan-type partial lipodystrophy, Emery-Dreifuss muscle dystrophy and progeria (premature aging).

How the mutations cause disease is an area of intense research in many laboratories. The observation that several mesodermal tissues are affected by the pathology suggests a defect in mesenchymal stem or progenitor cell function. Because lamin A directly interacts with DNA and chromatin, and sequesters transcription factors, we are investigating how lamin A mutations influence the epigenetic regulation of transcription and differentiation in cellular disease models. We have shown that the myodystrophic R453W lamin A mutation, and to a lesser extent, wild-type lamin A, negatively affects epigenetic regulation of expression of the myogenin gene in mouse myoblasts (Håkelien et al., 2008). Combining imaging and epigenetic strategies, we are currently examining how lamin A mutations affect chromatin organization, epigenetic environments and differentiation of mesenchymal stem cells.

Persons involved: Dr. Erwan Delbarre, Bente Marie Jacobsen, Andrew Reiner, Dr. Thomas Küntziger

Collaborators: Dr. Brigitte Buendia (CNRS, Institut Jacques Monod, Paris), Prof. Howard Worman ( Columbia University, New York ), Dr. Gisele Bonne (Institut de Myologie, Paris ).

 

 

 

 

 

 

 

 

 

 

 

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