IPEB transcription factor regulating the intracisternal a particle gene during F9 cell differentiation is expressed at sites of lymphoid development

The murine intracisternal A particle (IAP) proviral elements are expressed at low levels in undifferentiated F9 embryonal carcinoma cells but are highly expressed when F9 cells are induced to differentiate into parietal endoderm‐like cells. IAP elements are also expressed in parietal endoderm‐like PYS‐2 cells. We previously identified an IAP proximal enhancer (IPE) element that mediates a F9 differentiation‐specific enhancer activity. We also identified a 60 kDa IPE binding (IPEB) protein whose activity is high in PYS‐2 cells, where IAP is expressed, but very low in F9 cells. Transcription of IAP elements has also been shown in the adult mouse thymus and in activated splenic B cells. We have now shown by DNA affinity chromatography, sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, and band‐shift analysis that the 60 kDa IPEB is expressed in adult T lymphocytes and in resting as well as lipopolysaccharide activated splenic B cells but not in adult liver cells, suggesting an important role for IPEB in IAP transcription in vivo. In addition, we find IPEB expressed in the fetal mouse at sites of lymphoid development, such as the liver, spleen, and thymus, suggesting it may play an important role in gene expression during lymphoid development. In support of this, we find IPEB in the human T cell tumor lines, Jurkat and Molt 13, as well as the Daudi B cell line and in the normal calf thymus and in the thymus and spleen of the chicken and rat. © 1995 Wiley‐Liss, Inc.