TGF‐β induces apoptosis and inhibits the proliferation of EBV‐negative B‐lymphoma cell lines. In contrast, EBV‐immortalized B cells are resistant to both the proapoptotic and the antiproliferative activities of TGF‐β. We have generated a lymphoblastoid cell line, in which we can switch on and off the EBV‐specific transcriptional program driven by EBNA2. When these cells express the EBNA2‐driven phenotype, they are resistant to TGF‐β‐mediated growth arrest. We used this cell line to readdress the question of how EBV can overcome the antiproliferative TGF‐β activity. We show here that EBV‐driven cells remain TGF‐β‐responsive since TGF‐β target genes are readily induced. Thus, EBV can overcome TGF‐β‐mediated growth arrest without interfering with the core machinery of the TGF‐β signaling pathway, which links ligand binding to the induction of TGF‐β target genes. © 2002 Wiley‐Liss, Inc.

Transcriptional regulation can occur at the level of initiation and RNA elongation. We report that the rearranged, nontranscribed Ig kappa gene in the pre-B cell line 70Z/3 harbors a paused RNA polymerase II (pol II) at a position between 45 and 89 bp downstream of the transcription initiation site. LPS, an inducer of NF-kappa B, activated Ig kappa gene transcription by increasing the processivity of pol II. TGF-beta inhibited the LPS-induced transcription of the Ig kappa gene, but not initiation and pausing of pol II. A rearranged copy of the Ig kappa gene was introduced into 70Z/3 cells using an episomal vector system. The episomal Ig kappa was regulated by LPS and TGF-beta like the endogenous gene and established a paused pol II, whereas a construct with a deletion of the intron enhancer and the C region did not establish a paused pol II. Two distinct functions can therefore be assigned to the deleted DNA elements: loading of pol II to its pause site and induction of processive transcription upon LPS stimulation. It had been proposed that somatic hypermutation of Ig genes is connected to transcription. The pause site of pol II described in this work resides upstream of the previously defined 5' boundary of mutator activity at Ig kappa genes. The possible role of pausing of pol II for somatic hypermutation is discussed.