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 α (hu GDI α) and another human Rab GDI, as human Rab GDI β (hu GDI β). Hu GDI α cDNA encodes a protein of 447 amino acids with a deduced molecular weight of 50,200. Northern blot analysis revealed that hu GDI α gene is expressed abundantly in the brain but much less in other tissues, while hu GDI β gene is ubiquitously expressed. All human neuroblastoma cell lines and tumor specimens examined express hu GDI α gene to various extents, while a human T cell leukemia cell line, MOLT3, does not. The levels of both hu GDI α and β 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 α gene expression is not related to the differentiation state of neuronal cells.
This work was supported in part by a grant for Cancer Research from the Hyogo Total Health Association (1994).