Rab
proteins, a family of Ras-related small
GTP-binding proteins, play a key role in regulating intracellular vesicle trafficking. Rab
GDP dissociation inhibitor (GDI3) forms a soluble complex with Rab
proteins and thereby prevents the exchange of
GDP for
GTP. Recently, two
isoforms of
Rab GDI cDNA were isolated from rats and mice. In this study, we have isolated a brain-type
isoform of human
Rab GDI cDNA and examined its expression in
neuroblastoma. We tentatively designate it as human
Rab GDI alpha (hu GDI alpha) and another human
Rab GDI, as human
Rab GDI beta (hu GDI beta). Hu GDI alpha
cDNA encodes a
protein of 447
amino acids with a deduced molecular weight of 50,200. Northern blot analysis revealed that hu GDI alpha gene is expressed abundantly in the brain but much less in other tissues, while hu GDI beta gene is ubiquitously expressed. All human
neuroblastoma cell lines and
tumor specimens examined express hu GDI alpha gene to various extents, while a human
T cell leukemia cell line, MOLT3, does not. The levels of both hu GDI alpha and beta
mRNA were constant in a human
neuroblastoma cell line, NB1, during its neuronal differentiation, while Rab3A and neurofilament-L gene expression and the number of neurosecretory granules were elevated at this condition. These results suggest that hu GDI alpha gene expression is not related to the differentiation state of neuronal cells.