Expression of the intracisternal A-particle is elevated during differentiation of embryonal carcinoma cells.

Abstract

Three cDNA clones coding for the 3' region of the intracisternal A-particle (IAP), a mouse endogenous retrovirus, were isolated during screening of a library for genes whose expression was modulated during the retinoic acid-induced differentiation of the embryonal carcinoma cell line F9 into parietal endoderm-like (PE-like) cells. In contrast to previously reported results, no IAP transcripts were detected in either F9 cells or two pluripotent cell lines tested. Instead, IAP transcripts as well as IAPs were abundant in the PE-like cells PYS-2 and F9AcCl 9 and in retinoic acid-induced F9 cells but not in the other differentiated cell types of teratocarcinoma origin which were examined. A comparison of the nucleotide sequences of the three IAP cDNA clones with a genomically integrated proviral sequence (MIA14) demonstrated heterogeneity in both length and sequence among the clones. The position of the poly(A) addition site was determined to be 15 nucleotides from the proposed poly(A) addition signal and to occur after the sequence CAGA, not CA, as previously proposed.Length heterogeneity was greatest in a region of TC repeats 80 base pairs 5' to the poly(A) addition site. Additionally, the putative TATAA box found in MIA14 was deleted in the cDNA clones and in the long terminal repeat regions from two other genomic clones examined. The heterogeneity evident among the cDNA clones further demonstrated that at least two distinct IAP genes are activated during differentiation. An analysis of the rate of transcription in isolated nuclei indicated that the activation of expression of IAP genes in PE-like cells is the result of transcriptional regulation. Together, these observations suggest that the modulation of IAP transcription is regulated autonomously rather than by the fortuitous integration of an IAP sequence adjacent to a developmentally regulated cellular gene.Analyses of gene regulation during early mammalian embryogenesis have been greatly aided by the availability of the murine embryonal carcinoma (EC) cell system, an in vitro model of early embryogenesis, and by the ability to clone genes that are differentially expressed during development. EC cells, derived from teratocarcinoma stem cells (19), share many antigenic and biochemical properties with ectoderm cells of the inner cell mass, including the ability to differentiate initially to endoderm cells (13,16,35). The F9 EC cell line, which is nullipotent and has a low frequency of spontaneous differentiation (5), has proven to be a particularly useful model, since these cells differentiate upon treatment with retinoic acid (RA) or RA plus dibutyryl cyclic AMP (dbcAMP) into cells that resemble the parietal endoderm (PE) of embryos. For instance, these PE-like cells synthesize and secrete the extracellular matrix components laminin, type IV collagen, entactin, and heparin sulfate proteoglycan (39, 40).To date, only a few molecular clones have been generated from either differentiated embryonic or teratocarcinomaderived cells. These include cDNA clones for ty...

Loss of intracisternal A-type retroviral particles in BL6 melanoma cells transfected with MHC class I genes

“…In some embryonic carcinoma lines after induction of their differentiation by retinoic acid (RA), a reduction but not a complete elimination of IAP production was observed that paralleled with a reduction in lAP mRNA expression (Hojman-Montes de Oca eta [., 1983). However, in other experiments RA-induced differentiation of embryonal carcinomas resulted in an increase in IAP expression (Howe & Overton, 1986). In BL6 melanoma cells expressing the endogenous or transfected H-2K b gene, loss of lAPs was not associated with an increase in differentiation or loss of malignant properties.…”

Intracisternal A-type particle-mediated activations of cytokine genes in a murine myelomonocytic leukemia: generation of functional cytokine mRNAs by retroviral splicing events.

“…The transcriptional activation of IAP sequences appears to be under the control of a complex series of regulatory proteins (11)(12)(13)31) and is influenced by such variables as DNA methylation (14,29,35) and the state of cellular differentiation (21) or transformation (1). Activation of cellular genes by local insertion of IAP sequences has been postulated to be due to one of at least three general mechanisms: the introduction of a cis-acting IAP LTR enhancer either 5' (37, 49, 50) or 3' (44,45) to the gene; the more theoretical possibility of separating the promoter of a cellular gene from 5' inhibitory sequences by the intervening insertion of an IAP sequence; and the introduction of an alternative, LTR-encoded promoter 5' to the cellular gene (9,23,37,46,49,50).…”

The Intracisternal A-Particle Proximal Enhancer-Binding Protein Activates Transcription and Is Identical to the RNA- and DNA-Binding Protein p54nrb/NonO

“…In our analyses of the mechanism by which IAP expression becomes activated, we have found that IAP gene expression in murine F9 EC cells, which resemble early embryonic cells, is restricted, whereas upon differentiation of these cells into parietal endoderm-like cells, IAP expression becomes highly activated. IAP expression is also activated in the parietal endoderm cell line PYS-2 (18). Two DNA elements have been identified.…”