Pretranslational control of tyrosine aminotransferase synthesis by 8-bromo-cyclic AMP in H-4 rat hepatoma cells

Decreased heat shock response upon adipose differentiation of 3T3-L1 cells

In order to gain a better understanding of the regulation of heat shock gene (hsp) expression in terminal cell differentiation, we evaluated the effects of heat shock on the synthesis of HSPs, the abundance of mRNAhsp, and the heat shock transcription factor (HSTF) DNA-binding activity in the 3T3-L1 fibroblasts and adipocytes. We showed that the heat shock (42 degrees C) induction of synthesis of HSPs was significantly greater in the undifferentiated fibroblast than the differentiated adipocyte cultures. In particular, the heat shock induced synthesis of HSP 72 was at least 10 times greater in the fibroblasts than in the adipocytes. Analysis of mRNA of hsp 89 alpha, hsp 89 beta, hsp 70, and hsp 25 by Northern blot hybridization showed that the expression of these mRNAs was very, if not strictly, dependent on heat shock of the cells; the abundance of these heat inducible mRNAs was significantly higher in fibroblasts than in adipocytes. Quantitation of the HSTF DNA-binding activity by gel retardation assay demonstrated a specific decrease in this activity in the differentiated cells. These results provide evidence of a decreased transcriptional activation of heat shock genes upon adipose cell differentiation.

The effect of cyclic AMP on the accumulation of newly synthesized protein in the extracellular matrix of PFHR-9 teratocarcinoma cells

The effect of elevated cyclic AMP levels on the accumulation of newly synthesized extracellular matrix protein was examined in PFHR-9 cells producing Type IV collagen. The effect of dbcAMP, 8-BrcAMP, IBMX and forskolin on the synthesis of total protein, non-collagen protein and collagen were compared. DbcAMP increased the accumulation of total protein but did not affect the distribution of collagen and non-collagen protein. 8-BrcAMP, IBMX and forskolin also increased collagen and non-collagen accumulation. However, the effect on collagen was significantly greater with 8-BrcAMP and IBMX. Consequently, 8-BrcAMP and IBMX resulted in an increased percent collagen synthesis in the extracellular matrix. Elevated cAMP levels had no effect on cell proliferation or DNA synthesis but did produce a significant effect on cell morphology.

Regulation of lactate dehydrogenase gene expression by cAMP-dependent protein kinase subunits

The studies described in this report suggest a rather complex, albeit incomplete, sequence of molecular events that we believe form part of the cascade of reactions through which a series of hormones, via cAMP, regulates the expression of specific gene products. The majority of our own studies relate to cAMP-mediated induction of LDH. Some, if not all, of the molecular steps discussed in this paper may ultimately be recognized as part of a universal mechanism by which cAMP controls gene expression in higher eukaryotes. The idea of a functional role for cAMP-dependent protein kinase subunits in cAMP-mediated gene control has already had experimental support, but our identification of the regulatory subunit RII as a topoisomerase now more firmly points to a complex function for the kinase in regulating gene function at the DNA level. We look forward to the elucidation of the function of those nuclear proteins that serve as substrate for the catalytic subunit of cAMP-dependent protein kinase. Further studies related to the molecular interaction of RII with chromosomal DNA should be a fruitful area for future research.

Biochemical aspects of orthodontic tooth movement. I. Cyclic nucleotide and prostaglandin concentrations in tissues surrounding orthodontically treated teeth in vivo

The objective of this study was to extract and assay cyclic nucleotides and prostaglandins from tissues surrounding orthodontically treated canines in cats. Seven groups of three to five female cats were treated by 80 g tipping force to one maxillary canine for 0 to 28 days. Tissue samples were removed from sites of compression and tension around treated teeth, and from the corresponding control sites. Cyclic nucleotides and prostaglandins were simultaneously extracted by a solvent system at 0 to -5 degrees C. A portion of the aqueous fraction was used for cAMP assay by a binding protein method; cGMP was purified by column chromatography and measured by radioimmunoassay. The solvent fraction was dried, reconstituted with assay buffer, and each of the prostaglandins measured by radioimmunoassay. Analysis of variance showed no significant differences between summary control and treated sites at each of the time periods studied. However, when interactions at secondary and tertiary levels were considered (such as tension and compression, position [apical-gingival sites] of tissue sample, and jaws), significant differences were found in PGE, cAMP, and PGF2 alpha values. These results demonstrate that alterations in the levels of each of these substances in tissues surrounding teeth may be brought about by long-term applications of orthodontic force in vivo. The method of tissue sampling, however, does not permit measurement of the levels of these substances in target cells alone, thus diluting the acute response that may have occurred in these cells.

Insulin enhances transcription of the tyrosine aminotransferase gene in rat liver

The mechanism of insulin-mediated induction of tyrosine aminotransferase in rat liver was investigated using a cloned cDNA probe. The level of aminotransferase mRNA increases about fourfold following administration of the hormone. This induced mRNA accumulation does not require de novo protein synthesis. Nuclear runoff transcription assays in isolated liver nuclei demonstrate that insulin has a rapid and time-dependent stimulatory effect on aminotransferase gene transcription. The magnitude of enhanced transcription can fully account for the increase in the mRNA. We conclude that the induction of tyrosine aminotransferase in rat liver by insulin is primarily a consequence of a selective increase in the rate of transcription of the aminotransferase gene.

Cyclic AMP as a transcriptional inhibitor of upper eukaryotic gene transcription

Recently, glucagon and its second messenger, cyclic AMP, have been shown to stimulate the transcription rate of several upper eukaryotic genes (1-5). We show here that glucagon can also block gene transcription. Both glucagon and cyclic AMP were found to inhibit the transcription of the genes encoding three liver glycolytic enzymes, including L-type pyruvate kinase and aldolase B. Thus, cyclic AMP proves to be not only an activator but also an inhibitor of gene transcription in eukaryotes.