The publication data currently available has been vetted by Vanderbilt faculty, staff, administrators and trainees. The data itself is retrieved directly from NCBI's PubMed and is automatically updated on a weekly basis to ensure accuracy and completeness.
If you have any questions or comments, please contact us.
Activated ras genes transform REF52 cells only at low frequencies and adenovirus early region 1A collaborates with ras oncogenes to convert REF52 cells to a tumorigenic phenotype. While failure to transform did not result from an absence of ras gene expression, E1A appeared to enhance expression of transfected ras genes by approximately tenfold. However, enhanced ras expression alone does not account for collaboration by E1A since overexpression of T24 Ha-ras p21 induced morphological crisis and cell growth arrest rather than stable transformation. These results indicate that E1A contributes complementing biochemical activities that enable ras genes to transform REF52 and suggest that the role of E1A in primary cell transformation may extend beyond facilitating in vitro establishment.
Selective transcription of the insulin gene in pancreatic beta cells is regulated by its enhancer, located within the 5'-flanking region of the insulin gene. Transcription from the enhancer is controlled by both positive- and negative-acting cellular transcription factors. It was previously shown that both the 243- and 289-amino-acid adenovirus type 5 E1a proteins can repress insulin gene transcription in vivo. To localize the insulin DNA sequences involved in this response, we examined the effects of a number of mutations within the 5'-flanking region of the rat insulin II gene on E1a-mediated repression of insulin gene transcription. We have found that E1a proteins inhibit enhancer-stimulated transcription of the insulin gene. The enhancer appears to contain at least two genetically separable and independent E1a target sequence elements. Interestingly, these same regions of the insulin enhancer have been shown to be negatively regulated by cellular transcription factors. These results suggest that E1a-like cellular factors may function in the pancreatic beta-cell-specific expression of the insulin gene.
The phenotype of a differentiated cell results from the expression of a unique set of genes in that cell. The differentiation of F9 teratocarcinoma cells in response to retinoic acid and cyclic AMP is an excellent example of this process, as the appearance of several gene products during the course of the differentiation process has been documented. In principle, the activation of gene expression could be due to the appearance of positive-acting factors, the loss of negative-acting factors, or a combination of both. Since F9 cells have been shown to express a cellular E1A analog whereas differentiated F9 cells do not, and it is known that the viral E1A gene exerts a negative effect on transcription of both viral and cellular genes, we determined whether the cellular genes activated during F9 cell differentiation are subject to E1A negative control. We found that infection of differentiated F9 cells with wild-type adenovirus resulted in a decline in the levels of collagen type IV mRNA and plasminogen activator mRNA, both of which are induced by differentiation. At least for the collagen gene, this phenomenon appears to involve a transcriptional repression.
Adenovirus E1A dependent trans-activation of transcription involves the utilization of cellular promoter specific transcription factors. One such factor termed E2F is important for the transcription of the viral E2 gene and appears to be a rate limiting component targeted during the trans-activation event. Since E2F is of cellular origin and likely to be involved in cellular gene control, we have identified E2F binding sites in cellular genes. Examples include the c-myc, c-myb and N-myc protoncogenes, the DHFR gene and the EGF receptor gene. The transcription of these genes is regulated by cell proliferation signals and each falls into the so-called immediate early class: genes that are activated independent of new protein synthesis. Because of these common properties of regulation, we have addressed the possible role of E2F in growth factor dependent activation of transcription. Expression of a c-myc promoter driven CAT gene, transfected into quiescent 3T3 cells, is stimulated by serum addition whereas an identical gene containing mutations in the E2F binding sites is not responsive. The DNA binding activity of E2F is increased 4-fold upon serum stimulation and the kinetics of activation parallel activation of c-myc transcription. Furthermore, this increase in E2F activity is independent of new protein synthesis indicating that serum stimulation results in an activation of a pre-existing factor. These results thus provide strong evidence linking E2F and proliferation dependent control of transcription. We also believe that the E2F transcription factor is the first example of a regulator of the class of immediate early genes that is slowly activated by stimulation of cell proliferation.