Role of the Rap1 GTPase in astrocyte growth regulation.
Tuberous sclerosis complex (TSC) is an autosomal dominant syndrome in which affected individuals develop nervous system abnormalities that might reflect astrocyte dysfunction. The TSC2 gene product, tuberin, encodes a GTPase-activating protein (GAP) domain, which regulates the activity of Rap1 in vitro. To determine whether dysregulated Rap1, resulting from TSC2 inactivation, leads to increased astrocyte proliferation in vivo, we generated transgenic mice expressing activated Rap1(G12V) specifically in astrocytes. We observed no statistically significant difference in the number of astrocytes between wild-type and GFAP-Rap1(G12V) littermates in vivo; however, during log-phase growth, we observed a 25% increase in GFAP-Rap1(G12V) astrocyte doubling times compared to wild-type controls. This decreased proliferation was associated with delayed MAP kinase, but not AKT, activation. Lastly, to determine whether constitutive Rap1 activation could reverse the increased astrocyte proliferation observed in transgenic mice expressing oncogenic Ras(G12V), we generated transgenic mice expressing both Ras(G12V) and Rap1(G12V) in astrocytes. These double transgenic mice showed a striking reversion of the Ras(G12V) astrocyte growth phenotype. Collectively, these results argue that the tumor suppressor properties of tuberin are unlikely to be related to Rap1 inactivation and that Rap1 inhibits mitogenic Ras pathway signaling in astrocytes.
Apicelli
Anthony J
AJ
Department of Neurology, Washington University School of Medicine, St Louis, Missouri 63110, USA.
Uhlmann
Erik J
EJ
Baldwin
Rebecca L
RL
Ding
Hao
H
Nagy
Andras
A
Guha
Abhijit
A
Gutmann
David H
DH
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000201:enzymology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002455:Cell Division / Q000502:physiology*; D002478:Cells, Cultured; D002490:Central Nervous System / Q000201:enzymology* / Q000254:growth & development* / Q000503:physiopathology; D050760:Cyclin-Dependent Kinase Inhibitor p27; D015536:Down-Regulation / Q000235:genetics; D020935:MAP Kinase Signaling System / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary / Q000235:genetics; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014402:Tuberous Sclerosis / Q000201:enzymology* / Q000235:genetics / Q000503:physiopathology; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism
C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D020827:rap1 GTP-Binding Proteins; D018631:ras Proteins