BLANC - Blanc

Role of the SUMO modification pathway in development and disease – SUMOCHROME

Submission summary

Post translational modifications play key roles in controlling protein activity and hence cell function. Modification by ubiquitin is unusual in that the modifier itself is a polypeptide. A number of ubiquitin-like modifications have been described and, among these, the modification by SUMO (Small Ubiquitin-like Modifier) is one of the most extensively studied. While the list of known substrates does not cease to grow, only for a limited number the biological consequence of modification has been studied in detail. Most of the major SUMO substrates are nuclear, they include transcription factors or co-factors, chromatin-associated proteins including histones and chromatin modifying enzymes, oncogenes and tumor suppressors as well as proteins involved in DNA repair, recombination or chromosome structure. A simple, unifying function of sumoylation has remained elusive. If, in some cases, sumoylation was shown to regulate the substrate's protein function, enzymatic activity, localization and/or stability, the functions of this modification remains in large part obscure for the majority of these. Sumoylation is a highly dynamic process and the steady-state level of SUMO-conjugated proteins is maintained by a fine equilibrium between conjugating (E1, E2, E3) and de-conjugating (SENPs) activities. It is therefore likely that perturbation of this equilibrium will manifest itself in disease processes. Notably, the SUMO pathway has been involved in oncogenesis and neurodegerative diseases. The main objective of the proposed work is to better understand the mechanisms and functions of the SUMO pathway in both normal and pathologic cell/organism contexts. To this end, two distinct but complementary approaches are taken: a first, or 'structural' approach seeks to identify novel components of this pathway, whereas the second, more 'mechanistic' approach centers on the role of sumoylation in vivo. - The first axis seeks to identify novel protein components associated with this senzymatic pathway. Biochemical approaches will be used to identify novel E3 ligases. As in the ubiquitination system, in which E3 ligases function as part of larger multi-protein complexes, we will similarly aim to identify putative co-factors for yet characterized and newly identified SUMO E3 ligases. In addition, this work should lead to the identification of novel substrates, for which detailed functional analyses will be undertaken. - The second major axis is to better understand the role of sumoylation in development and disease using animal models and derived cell cultures deficient for sumoylation. In order to circumvent the problems of early embryonic lethality inherent to the total lack of sumoylation, we have recently developed a mouse line (Ubc9flox/flox) harbouring a conditional knock out of the Ubc9 gene which encodes the unique E2 SUMO conjugating enzyme. In parallel, we have generated a second mouse line (Ubc9flip/-) harbouring a conditional 'hypomorphic' allele for Ubc9. These animals, referred to as '1/4 dose', are expected to show global hyposumoylation (Ubc9-/- < Ubc9flip/- < Ubc9+/-). After their characterization, animals in which sumoylation has been conditionally inactivated (Ubc9flox/flox) or attenuated (Ubc9flip/-) will be used to explore several aspects of the role of the SUMO modification pathway in vitro and in vivo. Mice inactivated for the PIASy E3 ligase gene will also be included in the study. We will identify the tissues and/or organs preferentially targeted by the reduction of sumoylation. Another approach consists in inactivating/reducing sumoylation in the mouse hematopoïetic lineages in order to establish the developmental and pathogenic consequences. In the long term, similar studies will be conducted for the central nervous system and other tissues. Given that complete abrogation of Ubc9 expression in a given cell type population may simply lead to cell death, we will favor experiments performed under reduced Ubc9 expression, i.e. in Ubc9flip/- animals. Finally, biochemical and cellular approaches will be employed to study the fundamental cellular processes associated with sumoylation with particular emphasis on the mechanisms involved in cellular senescence. Notably, we will study the role of SUMO modification in the structure and function of SAHFs (senescence-associated heterochromatin foci) as well as in the regulation of telomere length. It is clear that knowledge of the basics of sumoylation biology should lead to a better understanding of many cellular based diseases.

Project coordination

Anne DEJEAN (INSTITUT PASTEUR)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

INSTITUT PASTEUR

Help of the ANR 400,000 euros
Beginning and duration of the scientific project: - 48 Months

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