Project description:Sequencing cancer genomes is predicted to uncover therapeutic tumor vulnerabilities. This has been complicated by the abundance of genetic alterations which are either non-functional, or only important in tumor initiation or progression. Distinguishing tumor maintenance genes from initiation, progression, and passenger genes is critical for developing effective cancer therapy. We employed a functional genomic approach using the Lazy Piggy transposon to identify tumor maintenance genes in vivo, and apply this to SHH medulloblastoma (MB). Combining Lazy Piggy screening in mice and transcriptomic profiling of human MB, we discovered candidate maintenance genes including the voltage-gated potassium channel Kcnb2. Genetic knockout of Kcnb2 impairs MB growth. Kcnb2 mediates potassium efflux in MB-propagating cells to govern cell volume. Loss of Kcnb2 leads to chronic osmotic swelling and decreased plasma membrane tension, which elevates endocytosis to dampen Egfr signaling, thereby mitigating proliferation of MB-propagating cells. Kcnb2 is largely dispensable for mouse development and synergizes with anti-SHH therapy in treating MB. These results demonstrate the utility of the Lazy Piggy functional genomic approach in identifying cancer maintenance genes, and elucidate a mechanism by which a potassium channel integrates biomechanical and biochemical signaling to promote MB aggression.
Project description:Sequencing cancer genomes is predicted to uncover therapeutic tumor vulnerabilities. This has been complicated by the abundance of genetic alterations which are either non-functional, or only important in tumor initiation or progression. Distinguishing tumor maintenance genes from initiation, progression, and passenger genes is critical for developing effective cancer therapy. We employed a functional genomic approach using the Lazy Piggy transposon to identify tumor maintenance genes in vivo, and apply this to SHH medulloblastoma (MB). Combining Lazy Piggy screening in mice and transcriptomic profiling of human MB, we discovered candidate maintenance genes including the voltage-gated potassium channel Kcnb2. Genetic knockout of Kcnb2 impairs MB growth. Kcnb2 mediates potassium efflux in MB-propagating cells to govern cell volume. Loss of Kcnb2 leads to chronic osmotic swelling and decreased plasma membrane tension, which elevates endocytosis to dampen Egfr signaling, thereby mitigating proliferation of MB-propagating cells. Kcnb2 is largely dispensable for mouse development and synergizes with anti-SHH therapy in treating MB. These results demonstrate the utility of the Lazy Piggy functional genomic approach in identifying cancer maintenance genes, and elucidate a mechanism by which a potassium channel integrates biomechanical and biochemical signaling to promote MB aggression.
Project description:Potassium (K+) is an essential physiological element determining membrane potential, intracellular pH, osmotic/turgor pressure, and protein synthesis in cells. Nevertheless, K+ homeostasis remains poorly studied in bacteria. Here we describe the regulation of potassium uptake systems in the oligotrophic -proteobacterium Caulobacter crescentus known as a model for asymmetric cell division. We show that C. crescentus can grow in concentrations from the micromolar to the millimolar range by essentially using two K+ transporters to maintain potassium homeostasis, the low affinity Kup and the high affinity Kdp uptake systems. When K+ is not limiting, we found that the kup gene is essential while kdp inactivation does not impact the growth. In contrast, kdp becomes critical but not essential and kup dispensable for growth in K+-limited environments. However, in the absence of kdp, mutations in kup were selected to improve growth in K+-depleted conditions, likely by improving the affinity of Kup for K+. In addition, mutations in the KdpDE two-component system, which regulates kdpABC expression, suggest that the inner membrane sensor regulatory component KdpD works as a kinase in early stages of growth and as a phosphatase to regulate transition into stationary phase. Our data also show that KdpE is not only phosphorylated by KdpD but also by another non-cognate histidine kinase. On top of this, we determined the KdpE-dependent and independent K+ transcriptome and identified the direct targets of KdpE. Together, our work illustrates how an oligotrophic bacterium responds to fluctuation in K+ availability.
Project description:Potassium (K+) is an essential physiological element determining membrane potential, intracellular pH, osmotic/turgor pressure, and protein synthesis in cells. Nevertheless, K+ homeostasis remains poorly studied in bacteria. Here we describe the regulation of potassium uptake systems in the oligotrophic -proteobacterium Caulobacter crescentus known as a model for asymmetric cell division. We show that C. crescentus can grow in concentrations from the micromolar to the millimolar range by essentially using two K+ transporters to maintain potassium homeostasis, the low affinity Kup and the high affinity Kdp uptake systems. When K+ is not limiting, we found that the kup gene is essential while kdp inactivation does not impact the growth. In contrast, kdp becomes critical but not essential and kup dispensable for growth in K+-limited environments. However, in the absence of kdp, mutations in kup were selected to improve growth in K+-depleted conditions, likely by improving the affinity of Kup for K+. In addition, mutations in the KdpDE two-component system, which regulates kdpABC expression, suggest that the inner membrane sensor regulatory component KdpD works as a kinase in early stages of growth and as a phosphatase to regulate transition into stationary phase. Our data also show that KdpE is not only phosphorylated by KdpD but also by another non-cognate histidine kinase. On top of this, we determined the KdpE-dependent and independent K+ transcriptome and identified the direct targets of KdpE. Together, our work illustrates how an oligotrophic bacterium responds to fluctuation in K+ availability.
Project description:Recent genomic approaches have suggested the existence of multiple distinct subtypes of medulloblastoma. We studied a large cohort of medulloblastomas to determine how many subgroups of the disease exist, how they differ, and the extent of overlap between subgroups. We determined gene expression profiles and DNA copy number aberrations for 103 primary medulloblastomas. Bioinformatic tools were used for class discovery of medulloblastoma subgroups based on the most informative genes in the dataset. Immunohistochemistry for subgroup-specific ‘signature’ genes was used to determine subgroup affiliation for 294 non-overlapping medulloblastomas on two independent tissue microarrays (TMAs). Multiple unsupervised analyses of transcriptional profiles identified four distinct, non-overlapping molecular variants: WNT, SHH, Group C, and Group D. Supervised analysis of these four subgroups revealed significant subgroup-specific demographics, histology, metastatic status, and DNA copy number aberrations. Immunohistochemistry for DKK1 (WNT), SFRP1 (SHH), NPR3 (Group C), and KCNA1 (Group D) could reliably and uniquely classify formalin fixed medulloblastomas in ~98% of cases. Group C patients (NPR3 +ve tumors) exhibited a significantly diminished progression free and overall survival irrespective of their metastatic status. Our integrative genomics approach to a large cohort of medulloblastomas has identified four disparate subgroups with distinct demographics, clinical presentation, transcriptional profiles, genetic abnormalities, and clinical outcome. Medulloblastomas can be reliably assigned to subgroups through immunohistochemistry, thereby making medulloblastoma sub-classification widely available. Future research on medulloblastoma and the development of clinical trials should take into consideration these four distinct types of medulloblastoma. A total of 103 primary medulloblastoma specimens were profiled by Affymetrix exon array and gene-level analysis was performed.