The evolutionarily conserved checkpoint protein kinase, TOR (target of rapamycin), has emerged as a major effector of cell growth and proliferation via the regulation of protein synthesis. Work in the last decade clearly demonstrates that TOR controls protein synthesis through a stunning number of downstream targets. Some of the targets are phosphorylated directly by TOR, but many are phosphorylated indirectly. In this review, we summarize some recent developments in this fast-evolving field. We describe both the upstream components of the signaling pathway(s) that activates mammalian TOR (mTOR) and the downstream targets that affect protein synthesis. We also summarize the roles of mTOR in the control of cell growth and proliferation, as well as its relevance to cancer and synaptic plasticity.

/pdf/upstream-and-downstream-of-mtor-2v5cvgfhmb.pdf

Upstream and downstream of mTOR

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by the formation of hamartomas in a wide range of human tissues. Mutation in either the TSC1 or TSC2 tumour suppressor gene is responsible for both the familial and sporadic forms of this disease. TSC1 and TSC2 proteins form a physical and functional complex in vivo. Here, we show that TSC1-TSC2 inhibits the p70 ribosomal protein S6 kinase 1 (an activator of translation) and activates the eukaryotic initiation factor 4E binding protein 1 (4E-BP1, an inhibitor of translational initiation). These functions of TSC1-TSC2 are mediated by inhibition of the mammalian target of rapamycin (mTOR). Furthermore, TSC2 is directly phosphorylated by Akt, which is involved in stimulating cell growth and is activated by growth stimulating signals, such as insulin. TSC2 is inactivated by Akt-dependent phosphorylation, which destabilizes TSC2 and disrupts its interaction with TSC1. Our data indicate a molecular mechanism for TSC2 in insulin signalling, tumour suppressor functions and in the inhibition of cell growth.

TSC2 is phosphorylated and inhibited by Akt and suppresses mTOR signalling

We tested the hypothesis that de novo copy number variation (CNV) is associated with autism spectrum disorders (ASDs). We performed comparative genomic hybridization (CGH) on the genomic DNA of patients and unaffected subjects to detect copy number variants not present in their respective parents. Candidate genomic regions were validated by higher-resolution CGH, paternity testing, cytogenetics, fluorescence in situ hybridization, and microsatellite genotyping. Confirmed de novo CNVs were significantly associated with autism (P = 0.0005). Such CNVs were identified in 12 out of 118 (10%) of patients with sporadic autism, in 2 out of 77 (3%) of patients with an affected first-degree relative, and in 2 out of 196 (1%) of controls. Most de novo CNVs were smaller than microscopic resolution. Affected genomic regions were highly heterogeneous and included mutations of single genes. These findings establish de novo germline mutation as a more significant risk factor for ASD than previously recognized.

/pdf/strong-association-of-de-novo-copy-number-mutations-with-1mq4l4g552.pdf

Strong Association of De Novo Copy Number Mutations with Autism

Tuberous sclerosis complex (TSC) is a genetic disease caused by mutation in either TSC1 or TSC2. The TSC1 and TSC2 gene products form a functional complex and inhibit phosphorylation of S6K and 4EBP1. These functions of TSC1/TSC2 are likely mediated by mTOR. Here we report that TSC2 is a GTPase-activating protein (GAP) toward Rheb, a Ras family GTPase. Rheb stimulates phosphorylation of S6K and 4EBP1. This function of Rheb is blocked by rapamycin and dominant-negative mTOR. Rheb stimulates the phosphorylation of mTOR and plays an essential role in regulation of S6K and 4EBP1 in response to nutrients and cellular energy status. Our data demonstrate that Rheb acts downstream of TSC1/TSC2 and upstream of mTOR to regulate cell growth.

/pdf/rheb-gtpase-is-a-direct-target-of-tsc2-gap-activity-and-50yowlaw8b.pdf

Rheb GTPase is a direct target of TSC2 GAP activity and regulates mTOR signaling

Many patients suffering from developmental disorders harbor submicroscopic deletions or duplications that, by affecting the copy number of dosage-sensitive genes or disrupting normal gene expression, lead to disease. However, many aberrations are novel or extremely rare, making clinical interpretation problematic and genotype-phenotype correlations uncertain. Identification of patients sharing a genomic rearrangement and having phenotypic features in common leads to greater certainty in the pathogenic nature of the rearrangement and enables new syndromes to be defined. To facilitate the analysis of these rare events, we have developed an interactive web-based database called DECIPHER (Database of Chromosomal Imbalance and Phenotype in Humans Using Ensembl Resources) which incorporates a suite of tools designed to aid the interpretation of submicroscopic chromosomal imbalance, inversions, and translocations. DECIPHER catalogs common copy-number changes in normal populations and thus, by exclusion, enables changes that are novel and potentially pathogenic to be identified. DECIPHER enhances genetic counseling by retrieving relevant information from a variety of bioinformatics resources. Known and predicted genes within an aberration are listed in the DECIPHER patient report, and genes of recognized clinical importance are highlighted and prioritized. DECIPHER enables clinical scientists worldwide to maintain records of phenotype and chromosome rearrangement for their patients and, with informed consent, share this information with the wider clinical research community through display in the genome browser Ensembl. By sharing cases worldwide, clusters of rare cases having phenotype and structural rearrangement in common can be identified, leading to the delineation of new syndromes and furthering understanding of gene function.

https://www.cell.com/ajhg/pdf/S0002-9297(09)00107-4.pdf

Martijn H. Bruening

Papers

Identification and characterization of the tuberous sclerosis gene on chromosome 16

Patient focused interventions and communication in the surgical clinic: a systematic review and meta-analysis