CELL-CYCLE REGULATION OF IMMUNOGLOBULIN CLASS SWITCH RECOMBINATION AND GERM-LINE TRANSCRIPTION - POTENTIAL ROLE OF ETS FAMILY MEMBERS

Previous studies have indicated that transcription of germ-line (GL) C -H genes is necessary to obtain immunoglobulin (Ig) class switching. W e report here a correlation between proliferation, switching and GL tr anscripts. S mu-S gamma 1 switch recombination in lipopolysaccharide ( LPS) + interleukin-4 (IL-4)-activated mouse B cells was assayed by a d igestion-circularization polymerase chain reaction. Switching to gamma 1 is reduced upon inhibition of DNA synthesis with hydroxyurea (HU) o r aphidicholin (AC). Incubation of activated B cells with HU severely reduces steady-state levels of GL gamma 1 and epsilon RNA. By utilizin g elutriation to synchronize B cell blasts in different phases of the cell cycle, it was found that GL gamma 1 transcripts are mainly expres sed in G(1) and S phases, but not in G(0). Using the electrophoretic m obility shift assay, we characterized two major LPS-induced complexes, which bind to the GL gamma 1 promoter and are expressed at levels whi ch correlate with the amount of LPS-induced DNA synthesis. Furthermore , the intensity of the complexes is reduced when cells are arrested wi th the DNA synthesis inhibitors HU or AC. Elutriation experiments reve aled that the complexes are expressed in G(1) and S, but not in G(0). They bind to an Ets consensus element near the major initiation sites used in proliferating cells. The possible implications of these findin gs for Ig isotype switching are discussed.