Regulation of JC virus expression in B lymphocytes

The etiologic agent of progressive multifocal leukoencephalopathy, a subacute demyelinating disease of the central nervous system, is the human polyomavirus JC virus (JCV), which causes a lytic infection of myelin-producing oligodendrocytes. In infected individuals the JCV genome can be detected in brain tissue and B lymphocytes isolated from the blood, bone marrow, or lymph nodes. Using mobility shift assays and a radiolabeled oligonucleotide from the JCV promoter-enhancer region (JCV bp 130 to 160), referred to as domain B, we were able to detect specific bands of the same mobility in nuclear extracts from human fetal glial cells, U-251 glioma cells, different B-cell lines, and in vitro-activated tonsillar B lymphocytes but not from T cells. In addition, a specific shift was detected when using nuclear extracts from freshly isolated tonsillar or lymph node B cells from five AIDS patients, two of whom later developed progressive multifocal leukoencephalopathy. Somewhat surprisingly, the above gel shift was partially inhibited by unlabeled oligonucleotides containing a kappa E2-binding site. UV cross-linking of the protein-DNA complex from either B cells or glial cells and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of a 46-kDa band. Transient transfection of a reporter plasmid constructed by fusing a trimer of the domain B sequence to a minimal promoter revealed activity in B lymphocytes and glial cells but not in T cells. Mutational analysis of this region demonstrated that the core TGGC repeat was essential for enhancer activity. Thus, a similar protein in B lymphocytes and glial cells may account for the preferential replication of JCV in these two cell types.