Enhanced expression of ganglioside GD3 in human and rat hepatocellular carcinoma cells and NIH 3T3 cells transfected with human tumor DNAs.

The gangliosides of human hepatoma biopsies, human hepatoma cell lines, and diethylnitrosamine-induced rat hepatomas were examined. These malignant tissues all expressed increased content of disialolactosylceramide (GD3) with respect to their normal counterparts. During the induction of rat hepatoma by diethylnitrosamine, an increase in GD3 levels appeared as early as 12 wk after initiation of diethylnitrosamine, concurrent with the appearance of precancerous hepatocytes. GD3 levels gradually increased to a peak of 4 times that of normal rat liver at 20 wk. CMP-NeuAc:GM3 sialyltransferase, the enzyme that synthesizes GD3 by transfer of sialic acid to GM3, also had tumor-associated elevation during the course of diethylnitrosamine-induction of rat hepatomas. To investigate the relationship of oncogene transformation and changes in ganglioside biosynthesis, NIH 3T3 cells transfected DNAs from human hepatoma or nasopharyngeal carcinoma were studied. The transfectants each expressed the same ganglioside composition, including a detectable level of GD3, as well as enhanced activity of CMP-NeuAc:GM3 sialyltransferase. A correlation between the tumor DNA transfection and the augmentation of GD3 in malignant cells is discussed. Because of the early appearance of GD3 in hepatoma and its possible relationship to oncogene activation, GD3 may be a potentially useful early tumor marker.

Transcription initiation region of the srfA operon, which is controlled by the comP-comA signal transduction system in Bacillus subtilis.

srfA is an operon required for the production of the lipopeptide antibiotic surfactin, competence development, and efficient sporulation in Bacillus subtilis. The expression of srfA is induced after the end of exponential growth and is dependent on the products of late-growth regulatory genes comP, comA, and spo0K. To begin to understand the mechanism of srfA regulation, the srfA promoter region was identified and characterized. To examine srfA promoter activity, the srfA promoter was fused to lacZ and inserted into the B. subtilis chromosome as a single copy at the SP beta prophage. The location of the transcription start site of srfA was determined by primer extension analysis and shown to be preceded by a sequence that resembles the consensus promoter recognized by the sigma A form of RNA polymerase. The srfA operon was found to have a sequence corresponding to a long, untranslated leader region of the srfA mRNA (300 bp). A nucleotide sequence and mutational analysis of the promoter identified a region of dyad symmetry required for srfA-lacZ expression. A similar sequence is found in the region upstream of the degQ promoter, transcription from which is also regulated by ComA. This region of dyad symmetry found upstream of these promoters may be the target for ComA-dependent transcriptional activation.