Differential effects of energy stress on AMPK phosphorylation and apoptosis in experimental brain tumor and normal brain.
BACKGROUND
AMP-activated protein kinase (AMPK) is a known physiological cellular energy sensor and becomes phosphorylated at Thr-172 in response to changes in cellular ATP levels. Activated AMPK acts as either an inducer or suppressor of apoptosis depending on the severity of energy stress and the presence or absence of certain functional tumor suppressor genes.


RESULTS
Here we show that energy stress differentially affects AMPK phosphorylation and cell-death in brain tumor tissue and in tissue from contra-lateral normal brain. We compared TSC2 deficient CT-2A mouse astrocytoma cells with syngeneic normal astrocytes that were grown under identical condition in vitro. Energy stress induced by glucose withdrawal or addition of 2-deoxyglucose caused more ATP depletion, AMPK phosphorylation and apoptosis in CT-2A cells than in the normal astrocytes. Under normal energy conditions pharmacological stimulation of AMPK caused apoptosis in CT-2A cells but not in astrocytes. TSC2 siRNA treated astrocytes are hypersensitive to apoptosis induced by energy stress compared to control cells. AMPK phosphorylation and apoptosis were also greater in the CT-2A tumor tissue than in the normal brain tissue following implementation of dietary energy restriction. Inefficient mTOR and TSC2 signaling, downstream of AMPK, is responsible for CT-2A cell-death, while functional LKB1 may protect normal brain cells under energy stress.


CONCLUSIONS
Together these data demonstrates that AMPK phosphorylation induces apoptosis in mouse astrocytoma but may protect normal brain cells from apoptosis under similar energy stress condition. Therefore, using activator of AMPK along with glycolysis inhibitor could be a potential therapeutic approach for TSC2 deficient human malignant astrocytoma.
Mukherjee
Purna
P
Department of Biology, Boston College, Chestnut Hill, Massachusetts 02467, USA. mukherjp@bc.edu
Mulrooney
Tiernan J
TJ
Marsh
Jeremy
J
Blair
Derek
D
Chiles
Thomas C
TC
Seyfried
Thomas N
TN
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D001253:Astrocytes / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D001254:Astrocytoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D015153:Blotting, Western; D001921:Brain / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D031204:Caloric Restriction; D002460:Cell Line; D045744:Cell Line, Tumor; D020287:In Situ Nick-End Labeling; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009097:Multienzyme Complexes / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D012265:Ribonucleotides / Q000494:pharmacology; D014162:Transfection; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
D009097:Multienzyme Complexes; D034741:RNA, Small Interfering; D012265:Ribonucleotides; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide