The human herpesvirus 8 homolog of Epstein-Barr virus SM protein (KS-SM) is a posttranscriptional activator of gene expression.

Homologs of the Epstein-Barr virus (EBV) SM protein exist in several human and nonhuman herpesviruses. Structure and function differ significantly among these proteins. We have cloned and characterized the human herpesvirus 8 (HHV8) gene, KS-SM, which is homologous to the EBV SM and herpes simplex virus ICP27 genes, from an HHV8-infected primary effusion lymphoma. KS-SM is shown to be a posttranscriptional activator of gene expression in cotransfection studies. KS-SM activated gene expression in a gene-specific, promoter-independent manner. In particular, KS-SM enhanced the expression of KDR/flk-1, a receptor for vascular endothelial growth factor (VEGF), in cotransfection studies. Since expression of KDR/flk-1 is increased in Kaposi's sarcoma and HHV8-infected cell cultures and VEGF enhances the proliferation of HHV8-infected cells, KS-SM may play a pathogenic role in Kaposi's sarcoma.