T S Papas

This book consists of 14 chapters. Some of the chapter heads are: Structural and Functional Motifs of the Rous Sarcoma Virus Src Protein, Activation of ras Oncogenes by Chemical Carcinogens, Structure and Function of p21 ras Proteins, Serum-Free Selection of Onc Genes, and Viral myc Genes and their Cellular Homologs.

A cDNA, which we call DRA (for down-regulated in adenoma) has been isolated. Its mRNA is expressed exclusively in normal colon tissue, probably only in the mucosal epithelia. Expression of the DRA gene is significantly decreased in adenomas (polyps) and adenocarcinomas of the colon. The DRA gene appears to be a single-copy gene present on chromosome 7, a chromosome associated with colorectal tumorigenesis. The predicted DRA polypeptide is an 84,500-Da protein that contains charged clusters of amino acids, primarily at the NH2 and COOH termini. Together with potential nuclear targeting motifs, an acidic transcriptional activation domain, and a homeobox domain, these elements suggest a transcription factor or a protein that may interact with transcription factors. Such a function may be consistent with a role in tissue-specific gene expression and/or as a candidate tumor-suppressor gene.

ets-1 and ets-2 genes have previously been identified by their sequence homology to the v-ets oncogene of the avian erythroblastosis virus, E26. These cellular genes have been shown to function as transcription factors important in lymphoid differentiation and activation and cellular proliferation. In this study, we have broadly analysed the differential expression of ets-1 and ets-2 during murine development using in situ hybridization. Our results indicate that these transcription factors are expressed in multiple tissues during critical stages of embryo formation and organogenesis, suggesting that these genes may serve multiple functions during mouse development. The patterns of expression of both genes are quite different as early as day 8.0 of gestation. ets-1 expression is clearly observed during a narrow developmental stage in the developing nervous system, including the presumptive hindbrain regions, the neural tube, as well as neural crest and the first and second branchial arches, ets-2 expression is limited to the developing limb buds and distal tail. At later times, ets-1 expression is observed in developing vascular structures, including the heart, arteries, capillaries and meninges, whereas ets-2 is highly expressed in developing bone, tooth buds, epithelial layers of the gut, nasal sinus and uterus, and several regions of the developing brain. Both ets-1 and ets-2 are expressed in developing lung, gut and skin. High levels of expression in both genes is observed in adult lymphoid tissues, but in different tissue subsets. ets-1 is expressed in the adult lung, gut mesenchyme and bone marrow. ets-2 continues to be expressed at low levels in several adult tissues, except in the differentiated brain, where substantial levels of expression are found in particular regions of the mature brain. These results demonstrate that ets-1 and ets-2 are differentially regulated, are widely expressed in many tissues during murine embryogenesis and may play important roles in cellular proliferation and differentiation during mouse development.

We have isolated a cDNA clone representing the complete coding sequence of a human gene named erg, related to the ets oncogene. Nucleotide sequence analysis of this cDNA (4.6 kilobases long) revealed that this gene encodes a 363-residue protein whose predicted amino acid sequence showed a homology of approximately equal to 40% and approximately equal to 70% to two domains corresponding to the 5' and 3' regions of v-ets oncogene, respectively. A 3.2- to 3.6-kilobase and approximately equal to 5-kilobase transcript of the erg gene, which differ in size from those of the previously described Hu-ets 1 and Hu-ets 2 genes, were observed in different cells. These results suggest that the erg gene is a member of the ets oncogene family.

The proto-oncogene ets-1 is a member of the ets family of genes that share homology with the viral oncogene, v-ets, of the avian leukemia virus E26. By using expression vectors, we demonstrate that the ets-1 gene transforms NIH3T3 cells and the ets-1 transfected cells form colonies in soft agar and induce tumors in nude mice. We have also determined that the ets-1 protein contains homology with the helix-loop-helix motif of the HLH family proteins, but lacks the basic domain upstream of helix I. Transfection of the NIH3T3 cells with ets-1 vectors results in the activation of the endogenous ets-1 gene. Using hybridization probes that can distinguish between transcripts from endogenous and exogenous templates, we show that the endogenous ets-1 gene is activated by the expression of the transfected exogenous ets-1. In contrast, the expression of transfected ets-2 has no effect on the endogenous ets-1 gene expression. The results indicate that the ets-1 proto-oncogene is positively autoregulated by its product.