Small GTP-binding proteins in human endothelial cells

Small GTP-binding proteins of the Ras superfamily control an extensive number of intracellular events by alternating between GDP- and GTP-bound conformation, The presence of members of this protein family was examined in human umbilical vein endothelial cells employing RT-PCR, Sequence analysis of 215 cDNA clones revealed the presence of a total of 28 different partial cDNAs encoding small GTP-binding proteins, Two sequences corresponded to novel isoforms of Rab2 and Rab9. In addition, human analogues of Rab4b, Rab7, Rab9, Rab14 and Rab15 were identified. Besides Rab proteins, members of other subfamilies were detected as well. As a first step towards elucidation of the function of the different small GTP-binding proteins identified we have isolated full length cDNA corresponding to Rab30 from a human endothelial cell cDNA library. In order to assess the subcellular localization of Rab30. we expressed epitope-tagged Rab30 cDNA in monkey kidney COS-1 cells. Immunoelectronmicroscopy of transfected COS-1 cells indicated that Rab30 is associated with Golgi stacks.