A Rap guanine nucleotide exchange factor enriched highly in the basal ganglia.
Ras proteins, key regulators of growth, differentiation, and malignant transformation, recently have been implicated in synaptic function and region-specific learning and memory functions in the brain. Rap proteins, members of the Ras small G protein superfamily, can inhibit Ras signaling through the Ras/Raf-1/mitogen-activated protein (MAP) kinase pathway or, through B-Raf, can activate MAP kinase. Rap and Ras proteins both can be activated through guanine nucleotide exchange factors (GEFs). Many Ras GEFs, but to date only one Rap GEF, have been identified. We now report the cloning of a brain-enriched gene, CalDAG-GEFI, which has substrate specificity for Rap1A, dual binding domains for calcium (Ca2+) and diacylglycerol (DAG), and enriched expression in brain basal ganglia pathways and their axon-terminal regions. Expression of CalDAG-GEFI activates Rap1A and inhibits Ras-dependent activation of the Erk/MAP kinase cascade in 293T cells. Ca2+ ionophore and phorbol ester strongly and additively enhance this Rap1A activation. By contrast, CalDAG-GEFII, a second CalDAG-GEF family member that we cloned and found identical to RasGRP [Ebinu, J. O., Bottorff, D. A., Chan, E. Y. W., Stang, S. L., Dunn, R. J. & Stone, J. C. (1998) Science 280, 1082-1088], exhibits a different brain expression pattern and fails to activate Rap1A, but activates H-Ras, R-Ras, and the Erk/MAP kinase cascade under Ca2+ and DAG modulation. We propose that CalDAG-GEF proteins have a critical neuronal function in determining the relative activation of Ras and Rap1 signaling induced by Ca2+ and DAG mobilization. The expression of CalDAG-GEFI and CalDAG-GEFII in hematopoietic organs suggests that such control may have broad significance in Ras/Rap regulation of normal and malignant states.
Kawasaki
H
H
Department of Brain and Cognitive Sciences, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Springett
G M
GM
Toki
S
S
Canales
J J
JJ
Harlan
P
P
Blumenstiel
J P
JP
Chen
E J
EJ
Bany
I A
IA
Mochizuki
N
N
Ashbacher
A
A
Matsuda
M
M
Housman
D E
DE
Graybiel
A M
AM
D000595:Amino Acid Sequence; D000818:Animals; D001479:Basal Ganglia / Q000378:metabolism*; D001921:Brain / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D002460:Cell Line; D017124:Conserved Sequence; D018076:DNA, Complementary; D005625:Frontal Lobe / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D015723:Gene Library; D006150:Guanine Nucleotides / Q000378:metabolism*; D006801:Humans; D007051:Ibotenic Acid; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D014162:Transfection; D020668:rap GTP-Binding Proteins
D018076:DNA, Complementary; D006150:Guanine Nucleotides; D012333:RNA, Messenger; D014157:Transcription Factors; D007051:Ibotenic Acid; D019204:GTP-Binding Proteins; D020668:rap GTP-Binding Proteins