Objective: Inheritance of a mutant allele of the SDF1 gene delays the onset of human immunodeficiency virus type 1 (HIV-1) disease. Because the mutation lies in the 3' untranslated region of the gene, it was suggested that this mutation may upregulate transcription of the gene, resulting in more abundant SDF1, which in turn inhibits T-tropic HIV-1 and delays disease onset. This implies that this segment of SDF1 gene contains a negative regulatory element. We directly tested this hypothesis in vitro.
Study design/methods: We cloned the wild-type and the mutant SDF1 gene in an HIV-2 gene transfer vector as well as in a baculovirus expression vector. We expressed the cloned genes in human and insect cells in culture and analyzed the abundance of SDF1 RNA by hybridization and protein using antiviral assays.
Results: The abundance of SDF1 RNA synthesized by the mutant clone with the mutation in the 3' untranslated region was no different from that synthesized by the wild-type clone in cultured cells. This was the case for both the HIV-2 long terminal repeat (LTR)-directed expression in human cells and baculovirus promoter-directed expression in insect cells. Both clones apparently synthesized SDF1 with equivalent biologic activity. Similar results were obtained for a mutant with the deletion of a GC-rich segment in the 5' untranslated region.
Conclusions: Mutation of the 3' untranslated exon did not affect SDF1 RNA synthesis in vitro. It also did not appear to affect translation of SDF1 RNA. A similar mutational analysis of the 5' noncoding exon suggested that this region also did not regulate SDF1 expression.