ANALYSIS OF OCT2-ISOFORM EXPRESSION IN LIPOPOLYSACCHARIDE-STIMULATED B-LYMPHOCYTES

Oct2-isoform expression in splenic B cells stimulated with lipopolysac charide or lipopolysaccharide plus phorbol-di-butyrate was analysed by cDNA cloning. The frequency of Oct2-positive clones was 1/15,000 in b oth libraries. Two new isoforms were found that generate novel amino- or carboxy-terminal sequences. An isoform lacking exon 11 destroyed th e carboxy-terminal leucin-zipper region and introduced a frame shift c reating a novel, proline-rich carboxy terminus. A new exon containing a highly basic region (4c) was characterized, between exons 4 and 5. T his exon was inserted between glutamine-rich regions 2 and 3, carboxy terminal of a tentative leucine-zipper structure. In addition, a new c ombination isoform containing Oct2a's amino terminal insert (exon 7a) and Oct2b's carboxy terminal insert (exon 13) was found that created a novel large isoform, Oct2ab. More frequent use of the classical Oct2a and Oct2b isoforms was observed in the lipopolysaccharide-stimulated B cells, while a preference for the Oct2ab and Oct2ba isoforms was obs erved in lipopolysaccharide plus phorbol-di-butyrate-treated cells.