Defective expression of adenovirus genes during early infection of undifferentiated OTF963 embryonal carcinoma cells

Abstract

Adenovirus infection was compared in F9 (OTF963) cells and cells induced to differentiate with retinoic acid, in order to study expression of early genes under the control of the reported "Ela-like factor" in F9 cells. However, not only was transcription of the viral Ela gene defective in undifferentiated cells but expression of all the other early genes was found to be reduced in OTF963 cells in comparison to differentiated cells. The defect in early gene expression was detected at the level of transcriptional initiation during the first 48 h of infection and resulted in similarly low levels of viral cytoplasmic mRNA and viral protein synthesis. Viral DNA replication was delayed and reduced. After 48 h of infection, the defect in transcription in OTF963 cells of Ela and other early genes was relieved, so that by 72 h postinfection the level of transcription was similar to that 16 h after infection of differentiated cells. At no time did adenovirus early gene expression occur independently of viral Ela. These results suggest limits to the generality and explanatory power of the hypothesis that F9 embryonal carcinoma cells contain an Ela-like factor. When embryonal carcinoma (EC) cells differentiate, radical changes in their morphology (44), proliferative rate (25, 38, 40), and tumorigenicity (45) are observed. F9 cells do not undergo spontaneous differentiation under normal culture conditions but can be induced to differentiate in vitro in the presence of retinoic acid into primitive endoderm-like cells (44), like those of the inner cell mass of the blastocyst (17). F9 cells treated with retinoic acid and dibutyryl cyclic AMP differentiate further to form either parietal or visceral endoderm (14, 46). EC cell lines have provided a useful in vitro model for the study of changes in gene regulation during differentiation (28). Genes encoding laminin B, collagen type IV, major histocompatibility complex class I antigens, P-2 microglobulin, Endo A, Endo B, and vinculin are transcriptionally activated 3 days postinduction. The cellular proto-oncogenes c-abl, c-src, and c-fos are also transcriptionally activated 1, 4, and 6 days postinduction of differentiation, respectively (28, 40). Viral genes have been used as a model system to investigate changes to gene regulation as a function of differentiation because they use cellular transcription factors and thus may reflect the regulation of cellular gene transcription. It has been found that transcription of several viral genes is repressed in undifferentiated F9 cells. However, if F9 cells are induced to differentiate, viral genes are expressed efficiently. The enhancer elements in the long terminal repeats of retroviruses, Moloney murine leukemia virus, murine sarcoma virus, and Rous sarcoma virus appear to be under negative control in undifferentiated F9 cells (10, 12, 13, 27, 49). The DNA viruses simian virus 40 (SV40), polyomavirus, and cytomegalovirus are all inactive in F9 cells due to a defect in the function of their early gene enhancers (11, 12, 32, 41, 42, 47, 4...

Convergent Regulation of NF-IL6 and Oct-1 Synthesis by Interleukin-6 and Retinoic Acid Signaling in Embryonal Carcinoma Cells

“…Contrary to predictions based on these results, differentiation of human NT2/D1 cells by IL-6 and by RA led to stimulation of ElA-independent viral replication. Studies of the ElA-substituting activities in other clones of mouse embryonal carcinoma cells, such as OTF963, also did not corroborate the observations made for F9 cells (27,28). The most likely explanation for these differences is that there is a clonal variation in the level of endogenous ElA-substituting activities in embryonal carcinoma cells and in their regulation during differentiation.…”