Cellular hypertrophy

• Control of protein accretion– Endogenous

• Nutrient status• Functional adequacy• History

– Exogenous• Nutrient availability• Growth factors• Space

• Protein synthesis (translation)

• Protein degradation (autophagy)

Immediate controls on protein synthesis

• Substrate availability– m-/t-RNA– Amino acids– Phosphatidylethanolamine (ATG8/LC3)

• Catalyst availability & activity– rRNA & S6 phosphorylation– eIF2, 4– eEF1, 2

Major regulatory pathways

• Positive– Akt: mTORc, inhibit FOXO– mTORc

• Growth Factors, nutrients, hypoxia

• S6k, 4E-BP1, inhibit ULK-1

• Negative– AMPK

• AMP/ATP, calcium

• ULK-1, TSC1/2, eEF2K

– FOXO (transcription factors)• Ubiquitin ligase, glutamine synthase (autophagy)

Signal integration through mTOR

TSC2

TSC1

RAPTOR

Ragulator

RAG

Lysosome

Rheb

Rheb

RAPTOR

GTP

GTP

GDPRAGGDP

PRAS40LST8

PRAS40LST8

mTOR

mTOR

AminoAcids

Insulin (GF)

Hypoxia

ATP/AMP

ERKAkt

AMPK

GSK3

REDD

Adhesion

Akt

Signal integration through AMPK

ATP/AMP

GSK3

mTOR

eEF2K

TFEAutophagy

Genes

ProteinSynthesis

eIF2b

p70etc

eEF2

eIF2aCa2+

CaMKK

LKB1

STRADMOL25a

ATM

DNA Damage

SympatheticNS

PKA

Glucose uptakeLipolysis

Mitochondria

AMPKAMPK

folliculin

AMPKa

FNIP

Stimuli for size change

• Developmental– Strongly dependent on growth factors– Feedforward

• Functional– Overload– Endogenous factors– Feedback

• Integrative– Autocrine/paracrine factors

Linking growth stimuli to growth

• Insulin/IGF-1 (growth factors, generally)– IGF1IGF1RIRS1

Grb2SOSRasRafMEKERKMNK--|4EBP1

PI3K

• PI3K– IGF1/FAKPI3KPIP3PDK1akt

--|TSC--|RhebmTORRSKS6translational apparatus

--|4EBP--|eIF4Etranslational activity

--|eEF2K--|eEF2translational activity

--|GSK3b--|eIF2translational activity

Physical niche is important

• Adhesion/turnover– IntegrinFAKSrc/paxillin

PI3KAktmTORc-Myc

– Transcriptional targets include eIFs, eEFs, tRNA synthetases, Pol III, nucleolar proteins, 40S & 60S proteins

CTD phosphorylation, mRNA cap methylation

ERK1/2

Huang & Ingber 1999

Cells grown on different attachment areas. Yellowsynthesizing DNABluenot synthesizing DNA

Negative controls on growth

• AMPK– AMPAMPK

TSC--|mTOR--|IRS1GSK3b--|eIF2

• FOXO, esp FOXO3– Oxidative/heat stress/Ppar-g FOXO

p27Kip--|cell cycleMuRF, atroginubiquitinylationmyostatin (FOXO1)

• TGF-b– TGFRSMADapoptosis, cell cycle arrest…

Paracrine signaling

• Positive– PGE2, PGF2a– GH/IGF-1 axis

• Negative– TGF-b family

Functional influences

• Muscle– Mechanical overload hypertrophy– Cell damage (creatine kinase)– Metabolite coupling (PPAR)

• Liver– Toxin overloadhypertrophy+hyperplasia– Cell damage (alanine aminotransferase)– Metabolite demand (PPAR)

• Epithelium– Competitive hypertrophy– Contact inhibition

Cell size transduction

• Mass action– Cube-square metabolite accumulation– Finite RNA/protein synthesis rates– Nucleus/cytoplasm volume (sc Cln3)– Diffusion (polar expression of Pom1)

• Contact– Cadherin--|b-catenincell cycle– Hippo/MST1/2--|Yki/Yapcell growth

Integrative control

• Mechanical demand– FAK, Ca2+, other force sensors

• Energetic demand– AMPK, GSK, Ragulator

• Net growth of cell depends on balance– Overloaded, high energy cell grows– Overloaded, starved cell atrophies– Infrequent overload is sufficient to maintain or

gain functional capacity

• mTOR is a signal integrator