TOR ( target of rapamycin) signaling Apr 4, 2005

serine/threonine protein kinase PI-3K-kinase related kinase (PIKK)superfamily Central role of TOR in cell growth and proliferation (disruption of gene encoding TOR results in lethality in all species)

TOR: integrator of nutrient and growth factor Coordinator of cell growth and proliferation Nutrients and Growth factor TOR Transcription, translation and ribosome biogenesis Cell growth (in crease in proliferating or non-proliferating cell mass and size via macromolecular biosynthesis) Cell proliferation (increase in cell number) Coupled, allowing cells to proliferate continuously while maintaining their size maintain individual cells, organs and whole organisms a characteristic size(Dysregulation of TOR signaling result in pathological changes in organ size, and diseases such as cancer, heart hypertrophy, muscular atrophy)

caAkt: Constitutively active Akt kdAkt: Kinase deficient Akt

Myostatin 肌抑素

 Discovery of rapamycin and identification of TOR  Structure of TOR protein  TOR signaling Upstream Downstream  TOR-binding proteins  TOR function  TOR and diseases  Future directions

Discovery of rapamycin and identification of TOR  1970s, rapamycin purification from Streptomyces hygroscopicus in Easter Island, antifungal activity  inhibit mammalian cell, especially immune system (B and T) cell proliferation as well as against solid tumors, potential immunosuppressant and anticancer drug  1989, FKBP12 (FK506-binding protein of 12 kDa, isomerase, protein folding) in Saccharomyces cerevisiae, direct receptor of rapamycin  1991, Genetic screens for mutations that rendered for S. cerevisiae resistant to the growth inhibitory effect of rapamycin identified two target of rapamycin proteins: TOR1 and TOR2

 , identification and cloning mTOR (mammalian target of rapamycin) from human rat and mouse. also named FRAP (FKBP-12-rapamycin-associated protein), RAFT (rapamycin and FKBP12 target), RAPT (rapamycin target) and SEP (sirolimus effector protein)  1999, TOR inhibitor rapamycin was approved as an immunosuppressant (inhibit kidney transplant rejection) and cardiology drug (restenosis after angioplasty 血管形成术后再狭窄 ) by FDA  rapamycin analogs CCI-779 and RAD001 are currently being tested in phase III clinical trials  An example of investigative power of “ Chemical genetics ” (use drugs or bioactive compounds as probes for dissection of signaling pathways)

 Structure of TOR protein  Large (290 kDa)  evolutionarily conserved (40-60% identical among mammals, flies, worms and yeast)  member of PIKK superfamily (MEC1, TEL1, RAD3, MEI41, DNA-PK, ATM, ATR and TRRAP)  HEAT repeats (Huntingtin, EF3, A subunit of PP2A and TOR motifs): 20 tandemly helical repeated, protein- protein interaction  FAT (FRAP-ATM-TRRAP) and FATC (FAT C-terminus): modulation of catalytic kinase activity  FRB (FKPP12-rapamycin binding domain)  Kinase domain  Repressor domain: auto-inhibitory domain

 Structure of mTOR protein

 TOR signaling (in mammalian cells)

 TOR upstream signaling  Growth factor/RTK  IRS: insulin receptor substrate  PI-3K/Akt/PKB  PTEN: phosphatase and tensin homologue deleted on chromosome ten (mutated in multiple advanced cancers, MMAC), a lipid phosphatase  PDK1: phosphoinositide-dependent protein kinase1  TSC1: tuberous sclerosis( 结节性脑硬化 ) complex 1(hamartin 错构瘤蛋白 );  TSC2 : tuberin 马玲薯球蛋白

 TOR upstream signaling  Rheb: small GTPase, TSC2 function as Rheb- GAP, shifting to Rheb-GDP;Rheb-GEF shifting to Rheb-GTP?  AMPK:AMP-dependent protein kinase  LKB1: key regulator of AMPK activity, mutated in Peutz-Jeghers Syndrome  Raptor: regulatory associated protein of mTOR  G  L(mammalian)or LST8 (yeast)

 TOR downstream pathway  S6K: p70 S6 kinase  S6 protein: 40S ribosomal protein, drive 5’ TOP (terminal oligopyrimidine tract) mRNA translation  4EBP1: eIF4E binding protein  eIF4E: eukaryotic translation initiation factor 4E recognizes the 5’ end cap of mRNA, increase key growth-promoting proteins, cyclin D1, c-Myc  cdks: cyclin-dependent kinase  pRb: protein retinoblastoma ( 眼癌 )  PP2A: protein phosphatase 2A

 TOR-binding proteins in yeast TORC1: AVO1, AVO2, AVO3, TOR2, LST8 controls actin organization, not a rapamycin target TORC2: TOR1, TOR2, KOG1, LST8

 TOR-binding proteins in mammalian cell raptor: regulatory associated protein of mTOR G  L: mammalian LST8,

 Raptor: regulatory associated protein of mTOR

 TOR function  Brain development learning and memory formation  apoptosis

 TOR inhibit autophagy

 TOR and apoptosis

 TOR and diseases  cancer  heart hypertrophy  muscular atrophy  Hamartoma syndromes  Inherited human dieases

 TOR and Cancers

mTOR and Hamartoma syndromes

Tor and Inherited human dieases

 Future directions  TOR deficiency in C. elegans doubles lifespan, whether TOR controls lifespan in mammals ?  How TOR senses and is activated by the presence of nutrients such as amino acid?  Downstream targets and cellular processes that are regulated by TOR  Role of TOR in apoptosis?  Understanding TOR signaling in neurons and muscle cells lead to new therapy for muscular wasting and memory impairment  TOR-binding proteins, gel filtration 2M