ABSTRACT
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.
Subject(s)
Basic Helix-Loop-Helix Transcription Factors/physiology , Hedgehog Proteins/metabolism , Neurons/metabolism , Receptors, Cell Surface/physiology , Stem Cells/metabolism , Ubiquitin-Protein Ligases/metabolism , Ubiquitin-Protein Ligases/physiology , Animals , Cell Differentiation , Cells, Cultured , Cerebellar Neoplasms/genetics , Cerebellar Neoplasms/metabolism , Cerebellar Neoplasms/mortality , Chromatography, Affinity , Female , Hedgehog Proteins/genetics , Humans , Male , Medulloblastoma/genetics , Medulloblastoma/metabolism , Medulloblastoma/mortality , Mice , Mice, Inbred C57BL , Mice, Knockout , Neurons/cytology , Patched Receptors , Phosphorylation , Proteolysis , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization , Stem Cells/cytology , Survival Rate , Tumor Suppressor ProteinsABSTRACT
YAP and its paralog protein TAZ are downstream effectors of the Hippo pathway. Both are amplified in many human cancers and promote cell proliferation and epithelial-mesenchymal transition. Little is known about the status of the Hippo pathway in cutaneous melanoma. We profiled Hippo pathway component expression in a panel of human melanoma cell lines and melanocytic lesions, and characterized the capacity of YAP and TAZ to control melanoma cell behavior. YAP and TAZ immuno-staining in human samples revealed mixed cytoplasmic and nuclear staining for both proteins in benign nevi and superficial spreading melanoma. TAZ was expressed at higher levels than YAP1/2 in all cell lines and in those with high invasive potential. Stable YAP or TAZ knockdown dramatically reduced the expression of the classical Hippo target CCN2/connective-tissue growth factor (CTGF), as well as anchorage-independent growth, capacity to invade Matrigel, and ability form lung metastases in mice following tail-vein injection. YAP knockdown also reduced invasion in a model of skin reconstruct. Inversely, YAP overexpression increased melanoma cell invasiveness, associated with increased TEA domain-dependent transcription and CCN2/CTGF expression. Together, these results demonstrate that both YAP and TAZ contribute to the invasive and metastatic capacity of melanoma cells and may represent worthy targets for therapeutic intervention.
Subject(s)
Adaptor Proteins, Signal Transducing/metabolism , Melanoma/metabolism , Phosphoproteins/metabolism , Skin Neoplasms/metabolism , Transcription Factors/metabolism , Acyltransferases , Adaptor Proteins, Signal Transducing/genetics , Animals , Cell Line, Tumor , Disease Models, Animal , Female , Gene Knockdown Techniques , Hippo Signaling Pathway , Humans , Lung Neoplasms/metabolism , Lung Neoplasms/secondary , Melanoma/pathology , Mice , Mice, Nude , Neoplasm Invasiveness , Neoplasm Transplantation , Phosphoproteins/genetics , Protein Serine-Threonine Kinases/metabolism , Signal Transduction/physiology , Skin Neoplasms/pathology , Transcription Factors/genetics , YAP-Signaling ProteinsABSTRACT
Huntington's disease (HD) is a fatal neurodegenerative disease, characterized by motor defects and psychiatric symptoms, including mood disorders such as anxiety and depression. HD is caused by an abnormal polyglutamine (polyQ) expansion in the huntingtin (HTT) protein. The development and analysis of various mouse models that express pathogenic polyQ-HTT revealed a link between mutant HTT and the development of anxio-depressive behaviors and various hippocampal neurogenesis defects. However, it is unclear whether such phenotype is linked to alteration of HTT wild-type function in adults. Here, we report the analysis of a new mouse model in which HTT is inducibly deleted from adult mature cortical and hippocampal neurons using the CreER(T2)/Lox system. These mice present defects in both the survival and the dendritic arborization of hippocampal newborn neurons. Our data suggest that these non-cell autonomous effects are linked to defects in both BDNF transport and release upon HTT silencing in hippocampal neurons, and in BDNF/TrkB signaling. The controlled deletion of HTT also had anxiogenic-like effects. Our results implicate endogenous wild-type HTT in adult hippocampal neurogenesis and in the control of mood disorders.
