Regulation of bcl-2 gene expression in lymphoid cell lines containing normal #18 or t(14;18) chromosomes

The bcl-2 (B cell lymphoma/leukemia-2) gene at band 18q21 is involved in t(14;18) chromosomal translocations in most follicular lymphomas and occasional other human B cell malignancies, where it becomes juxtaposed to the transcriptionally active immunoglobulin (Ig) locus at 14q32. Regulation of bcl-2 gene expression was investigated in neoplastic lymphoid cell lines containing normal #18 chromosomes or a t(14;18) translocation with regard to steady-state mRNA levels, RNA stability, transcription rates, and DNA methylation. High steady-state levels of bcl-2 mRNA, and proportionally high rates of bcl-2 transcription (measured in isolated nuclei), were found in B cell lines containing t(14;18) translocations. The half-life of bcl-2 mRNA (approximately 2-3 hr) was similar in all cell lines examined, including a t(14;18)-containing follicular lymphoma cell line, which has a translocated and rearranged bcl-2 gene that produces bcl-2/Ig fusion transcripts. However, in the presence of cycloheximide (inhibitor of protein synthesis), the half-life of some of the bcl-2/Ig mRNAs produced by these cells was prolonged, indicating that in some circumstances mRNA stability may contribute to deregulated bcl-2 expression. Despite stabilizing some bcl-2 mRNAs, the overall effect of treating cell lines with cycloheximide was a reduction in the levels of accumulated bcl-2 mRNAs through inhibition of bcl-2 gene transcription. These latter data provide indirect evidence that short-lived transacting factor(s) regulate transcription of the human bcl-2 gene in lymphoid cells with or without a t(14;18) translocation. No clear correlation was discovered between bcl-2 gene methylation and transcription.