Quiescence is essential for long-term maintenance of adult stem cells. Niche signals regulate the transit of stem cells from dormant to activated states. Here, we show that the E3-ubiquitin ligase ...Huwe1 (HECT, UBA, and WWE domain–containing 1) is required for proliferating stem cells of the adult mouse hippocampus to return to quiescence. Huwe1 destabilizes proactivation protein AscI1 (achaete-scute family bHLH transcription factor 1) in proliferating hippocampal stem cells, which prevents accumulation of cyclin Ds and promotes the return to a resting state. When stem cells fail to return to quiescence, the proliferative stem cell pool becomes depleted. Thus, long-term maintenance of hippocampal neurogenesis depends on the return of stem cells to a transient quiescent state through the rapid degradation of a key proactivation factor.
PEAK pseudokinases are molecular scaffolds which dimerize to regulate cell migration, morphology, and proliferation, as well as cancer progression. The mechanistic role dimerization plays in PEAK ...scaffolding remains unclear, as there are no structures of PEAKs in complex with their interactors. Here, we report the cryo-EM structure of dimeric PEAK3 in complex with an endogenous 14-3-3 heterodimer. Our structure reveals an asymmetric binding mode between PEAK3 and 14-3-3 stabilized by one pseudokinase domain and the SHED domain of the PEAK3 dimer. The binding interface contains a canonical phosphosite-dependent primary interaction and a unique secondary interaction not observed in previous structures of 14-3-3/client complexes. Additionally, we show that PKD regulates PEAK3/14-3-3 binding, which when prevented leads to PEAK3 nuclear enrichment and distinct protein-protein interactions. Altogether, our data demonstrate that PEAK3 dimerization forms an unusual secondary interface for 14-3-3 binding, facilitating 14-3-3 regulation of PEAK3 localization and interactome diversity.
During cerebellar development, granule neuron progenitors (GNPs) proliferate by transducing Sonic Hedgehog (SHH) signaling via the primary cilium. Precise regulation of ciliogenesis, thus, ensures ...proper GNP pool expansion. Here, we report that Atoh1, a transcription factor required for GNPs formation, controls the presence of primary cilia, maintaining GNPs responsiveness to SHH. Loss of primary cilia abolishes the ability of Atoh1 to keep GNPs in a proliferative state. Mechanistically, Atoh1 promotes ciliogenesis by transcriptionally regulating Cep131, which facilitates centriolar satellite (CS) clustering to the basal body. Importantly, ectopic expression of Cep131 counteracts the effects of Atoh1 loss in GNPs by restoring proper localization of CS and ciliogenesis. This Atoh1-CS-primary cilium-SHH pro-proliferative pathway is also conserved in SHH-type medulloblastoma, a pediatric brain tumor arising from the GNPs. Together, our data reveal how Atoh1 modulates the primary cilium to regulate GNPs development.
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•Atoh1 controls the presence of primary cilia in cerebellar granule neuron progenitors•Atoh1 requires the primary cilium to maintain the pool of proliferating progenitors•Atoh1 controls ciliogenesis by shaping centriolar satellites via its target Cep131
Chang et al. demonstrate how Atoh1 controls granule neuron progenitor proliferation during postnatal cerebellar development. By transcriptionally regulating Cep131, Atoh1 maintains the presence of the primary cilium, an organelle required for SHH signal transduction. This mechanism is also conserved in SHH medulloblastoma, a malignant pediatric brain tumor arising from the cerebellum.
Abstract
OTX2 is a potent oncogene that promotes tumor growth in Group 3 medulloblastoma. However, the mechanisms by which OTX2 represses neural differentiation are not well characterized. Here, we ...perform extensive multiomic analyses to identify an OTX2 regulatory network that controls Group 3 medulloblastoma cell fate. OTX2 silencing modulates the repressive chromatin landscape, decreases levels of PRC2 complex genes and increases the expression of neurodevelopmental transcription factors including
PAX3
and
PAX6
. Expression of PAX3 and PAX6 is significantly lower in Group 3 medulloblastoma patients and is correlated with reduced survival, yet only PAX3 inhibits self-renewal in vitro and increases survival in vivo. Single cell RNA sequencing of Group 3 medulloblastoma tumorspheres demonstrates expression of an undifferentiated progenitor program observed in primary tumors and characterized by translation/elongation factor genes. Identification of mTORC1 signaling as a downstream effector of OTX2-PAX3 reveals roles for protein synthesis pathways in regulating Group 3 medulloblastoma pathogenesis.
Signaling networks controlled by Sonic hedgehog (SHH) and the transcription factor Atoh1 regulate the proliferation and differentiation of cerebellar granule neuron progenitors (GNPs). Deregulations ...in those developmental processes lead to medulloblastoma formation, the most common malignant brain tumor in childhood. Although the protein Atoh1 is a key factor during both cerebellar development and medulloblastoma formation, up-to-date detailed mechanisms underlying its function and regulation have remained poorly understood. Here, we report that SHH regulates Atoh1 stability by preventing its phosphodependent degradation by the E3 ubiquitin ligase Huwe1. Our results reveal that SHH and Atoh1 contribute to a positive autoregulatory loop promoting neuronal precursor expansion. Consequently, Huwe1 loss in mouse SHH medulloblastoma illustrates the disruption of this developmental mechanism in cancer. Hence, the crosstalk between SHH signaling and Atoh1 during cerebellar development highlights a collaborative network that could be further targeted in medulloblastoma.
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•SHH regulates Atoh1 by preventing its degradation by the E3 ubiquitin ligase Huwe1•Atoh1 degradation via Huwe1 is required for neuronal migration and differentiation•SHH and Atoh1 contribute to an autoregulatory loop promoting neuron expansion•Low Huwe1 expression correlates with poor outcome in SHH-ATOH1 medulloblastoma
Signaling networks controlled by Sonic hedgehog (SHH) and the transcription factor Atoh1 control proliferation and differentiation in cerebellar development. Forget, Bihannic, et al. report that SHH regulates Atoh1 stability by preventing its phosphodependent degradation by the ubiquitin ligase Huwe1. Disruptions of this mechanism are later seen in SHH medulloblastoma.
GABAergic interneurons migrate long distances through stereotyped migration programs toward specific laminar positions. During their migration, GABAergic interneurons are morphologically alike but ...then differentiate into a rich array of interneuron subtypes critical for brain function. How interneuron subtypes acquire their final phenotypic traits remains largely unknown. Here, we show that cerebellar molecular layer GABAergic interneurons, derived from the same progenitor pool, use separate migration paths to reach their laminar position and differentiate into distinct basket cell (BC) and stellate cell (SC) GABAergic interneuron subtypes. Using two-photon live imaging, we find that SC final laminar position requires an extra step of tangential migration supported by a subpopulation of glutamatergic granule cells (GCs). Conditional depletion of GCs affects SC differentiation but does not affect BCs. Our results reveal how timely feedforward control of inhibitory interneuron migration path regulates their terminal differentiation and, thus, establishment of the local inhibitory circuit assembly.
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•Basket cells and stellate cells use stereotyped migration paths in cerebellum•Stellate cells migrate tangentially in the external granule cell layer•Immature granule cell neurites support stellate cell tangential migration•Genetic depletion of granule cells affects stellate cell differentiation
Cadilhac et al. report that molecular layer GABAergic progenitors use distinct migration paths to reach their laminar position in the cerebellum where they differentiate into basket cells (BCs) and stellate cells (SCs). SCs perform an additional tangential migration step along immature granule cell neurites whose genetic depletion mainly affects SC differentiation.
Current epidemics, such as AIDS or flu, and the emergence of new threatening pathogens, such as the one causing the current coronavirus disease 2019 (COVID-19) pandemic, represent major global health ...challenges. While vaccination is an important part of the arsenal to counter the spread of viral diseases, it presents limitations and needs to be complemented by efficient therapeutic solutions. Intricate knowledge of host-pathogen interactions is a powerful tool to identify host-dependent vulnerabilities that can be exploited to dampen viral replication. Such host-directed antiviral therapies are promising and are less prone to the development of drug-resistant viral strains. Here, we first describe proteomics-based strategies that allow the rapid characterization of host-pathogen interactions. We then discuss how such data can be exploited to help prioritize compounds with potential host-directed antiviral activity that can be tested in preclinical models.
Current epidemics, such as AIDS or flu, and the emergence of new threatening pathogens, such as the one causing the current coronavirus disease 2019 (COVID-19) pandemic, represent major global health ...challenges. While vaccination is an important part of the arsenal to counter the spread of viral diseases, it presents limitations and needs to be complemented by efficient therapeutic solutions. Intricate knowledge of host-pathogen interactions is a powerful tool to identify host-dependent vulnerabilities that can be exploited to dampen viral replication. Such host-directed antiviral therapies are promising and are less prone to the development of drug-resistant viral strains. Here, we first describe proteomics-based strategies that allow the rapid characterization of host-pathogen interactions. We then discuss how such data can be exploited to help prioritize compounds with potential host-directed antiviral activity that can be tested in preclinical models.
Medulloblastoma (MB) is a pediatric tumor of the cerebellum divided into four groups. Group 3 is of bad prognosis and remains poorly characterized. While the current treatment involving surgery, ...radiotherapy, and chemotherapy often fails, no alternative therapy is yet available. Few recurrent genomic alterations that can be therapeutically targeted have been identified. Amplifications of receptors of the TGFβ/Activin pathway occur at very low frequency in Group 3 MB. However, neither their functional relevance nor activation of the downstream signaling pathway has been studied. We showed that this pathway is activated in Group 3 MB with some samples showing a very strong activation. Beside genetic alterations, we demonstrated that an ActivinB autocrine stimulation is responsible for pathway activation in a subset of Group 3 MB characterized by high PMEPA1 levels. Importantly, Galunisertib, a kinase inhibitor of the cognate receptors currently tested in clinical trials for Glioblastoma patients, showed efficacy on orthotopically grafted MB‐PDX. Our data demonstrate that the TGFβ/Activin pathway is active in a subset of Group 3 MB and can be therapeutically targeted.
Synopsis
TGFβ/Activin signaling is activated in a subset of Group 3 medulloblastoma, through an ActivinB autocrine loop. ActivinB sustains tumor cell growth by inducing the expression of the Smad target gene PMEPA1. TGFβ/Activin pathway can be therapeutically targeted with Galunisertib in this G3 subgroup.
A subset of G3 medulloblastoma tumors displays high TGFβ/Activin pathway activation.
An ActivinB autocrine loop is responsible for TGFβ/Activin pathway activation in G3 medulloblastoma.
G3 medulloblastoma with strong TGFβ/Activin pathway activation are characterized by a high level of PMEPA1 expression.
Galunisertib treatment is of potential therapeutic interest for G3 medulloblastoma showing strong TGFβ/Activin pathway activation.
TGFβ/Activin signaling is activated in a subset of Group 3 medulloblastoma, through an ActivinB autocrine loop. ActivinB sustains tumor cell growth by inducing the expression of the Smad target gene PMEPA1. TGFβ/Activin pathway can be therapeutically targeted with Galunisertib in this G3 subgroup.
The class II transactivator (CIITA) is the master regulator of MHC class II molecules (MHC II). In melanoma, the MHC II are constitutively expressed due to an abnormal transcription of CIITA from its ...promoter III (pIII), and requires the presence of a 1‐kb enhancer located upstream from this latter. Since mitogen‐activated protein kinases (MAPK) have been shown to be activated in most melanomas, we sought to analyze their possible involvement in CIITA expression. Using chemical inhibitors and dominant‐negative constructs of MAPK‐ERK kinase (Mek1) and MAPK‐JNK, we evidenced the inhibition of MHC II and CIITA expression in melanoma cell lines displaying activated MAPK. Transcriptional regulation by MAPK is known to involve the AP‐1 transcription factor family. Sequence analysis revealed an AP‐1‐responsive motif in the enhancer of CIITA pIII at –5954/–5947 from the site of transcription initiation. Its mutagenesis reduced CIITA expression four‐ to fivefold in melanoma cell lines and alleviated the effect of dominant‐negative constructs of the MAPK pathway. Together, our findings demonstrate that MAPK‐ERK and MAPK‐JNK are regulators of CIITA transcription in melanoma, and pinpoint an AP‐1‐responsive site in the CIITA gene pIII. This should have considerable impact on our understanding of the physio‐pathologic expression of MHC II.
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