Expression in Human Endothelial Cells of ADP-ribosylation Factors, 20-kDa Guanine Nucleotide-binding Proteins Involved in the Initiation of Vesicular Transport

ADP-ribosylation factors (ARFs) are 20-kDa, guanine nucleotide-binding proteins, initially discovered as stimulators of cholera toxin ADP-ribosyltransferase activity and subsequently shown to participate in vesicular trafficking. Five of the six mammalian ARFs have been identified in human tissues by molecular cloning. They fall into three classes (class I: ARFs 1–3; class II: ARFs 4, 5; class III: ARF 6) based on deduced amino acid sequence, size, phylogenetic analysis, and gene structure. Similar to the rab family of 20 kDa guanine nucleotide-binding proteins, the ARFs appear to function in specific trafficking pathways. The presence of a specific ARF might serve as a marker for that pathway. To verify expression of ARF mRNA and protein in human umbilical vein endothelial cells, immunoreactivity using antibodies specific for each ARF class, quantitative polymerase chain reaction (PCR) using ARF-specific, internal cRNA standards containing unique restriction enzyme cleavage sites introduced by point mutations, and Northern analysis with probes specific for ARFs 1, and 3–6, were utilized. PCR and Northern analysis were in agreement in showing that amounts of mRNA for ARF 1 and ARF 4 were similar and higher than those of ARF 3 and ARF 5 which were greater than ARF 6. Primarily, Class I ARF proteins were detected by immunoreactivity, with the majority in the supernatant fraction. The relative expression of ARFs in endothelial cells thus differs from that in neuronal tissues where it had been found that ARF 3 is the predominant species.