Among postgenomic regulation, translation regulation is of critical importance in mammalian cell biology and enters completely in the postgenomic program developed by Genopole and UEVE. Here we will focus our interest on dedicated mRNA-binding proteins which are known to bias translation of a specific set of proteins by direct binding to mRNA. How RNA-binding proteins select specific transcripts in the cytoplasm remains however an open question. Among the mRNA-binding proteins which regulate mRNA translation are two members of the cold shock family, YB-1 andLin28, which plays a critical role in neuron development and differentiation and could be important target for cancerogenesis (Lin28,), multi-drug resistance (YB-1,) and neurogenesis (lin28, YB-1). The action of Lin28 is not only due to its targeting of Let7 miRNA but, as now recognized, also to its binding to mRNA for translation control critical in cell development. In a very recent study, we evidenced that YB-1 allows mRNPs to remain soluble while preventing the translation of the targeted mRNA and thus inhibits the formation of stress granules.
The laboratory has now acquired a recognized expertise in stress granule biology. The formation in the cell cytoplasm of “stress granules” containing mRNA and associated proteins like YB-1 and Lin28 occurs in response to various stresses like oxidative and osmotic stresses, hyperthermia, hypoxia, and some viral infections in all eukaryotic cells. However stress granules are not inert aggregates made of mRNA molecules and seem to fulfill important functions which are still debated like mRNA sorting, repair, degradation and reprogramming of mRNA translation machineries allowing cell recovery. In addition, cells need to resume global protein synthesis to allow an appropriate response to environmental stress, which necessitates the dissociation of stress granules. RNA-binding proteins like TDP-43 and FUS formed cytoplasmic inclusions in amyotrophic lateral sclerosis (ALS) and some types of frontotemporal lobar degeneration (FTLD) and may play a critical role for the onset of these diseases. In line with this, persistent stress granules may help the maturation of proteins aggregates made of prion-like proteins like TDP-43, FUS and polyubiquitinated proteins via their trapping in stress granules. Tau:RNA interaction could also be critical for the misorting of Tau into the neuron cell body and dendrites and its following aggregation in tauopathy.
In addition to the regulation of mature mRNA translation, most genes in higher eukaryotes are initially transcribed as pre-mRNAs from which intervening sequences are removed, yielding mature mRNAs, a process known as splicing. The catalysis of splicing occurs following the assembly of a large ribonucleoprotein complex on the pre-mRNA called the spliceosome. Interestingly, while investigating stress granule biology, many proteins found in the spliceosome like TDP-43, FUS and SMN1 were also found in stress granules. It is not yet understood whether alterations of the splicing mechanisms resulting from mutation (SMN1, FUS, TDP-43) or mislocation in the cytoplasm (FUS, TDP-43) contribute to neurodegeneration. Alternatively, we may wonder whether the cytoplasmic location of the splicing factors favors the formation stress granules and(or) their aggregation in cytoplasm which may be a critical step toward the understanding of neurodegeneration.
i. Studying the role of two major cold-shock proteins, YB-1 and Lin28, on the regulation of mRNA translation in order to derive a mechanistic model for the repression of specific mRNA by cold-shock proteins. Exploring their recently identified role as negative regulators of stress granule assembly.
ii. Examining the mechanisms leading to stress granule assembly using cellular and in vitro biophysical approaches and the interplay between the formation of stress granules and the genesis of protein aggregates containing TDP-43 and FUS in neurons. A strategy to limit the propensity of neurons to form protein aggregates in neurodegenerative diseases will be considered.
iii. Studying molecular aspects of the regulation of the RNA spicing in neuron and its link with neurodegeneration and rare genetic diseases (SMN). We will also investigate the intriguing relation between the mislocation of some RNA splicing factors (TDP-43, FUS) and their presences in cytoplasmic inclusions and(or)stress granules.