Insulin regulates the expression of more than 150 genes, indicating that this is a major action of this hormone. At least eight distinct consensus insulin response sequence (IRSs) have been defined through which insulin can regulate gene transcription. These include the serum response element, the activator protein 1 ('AP-1') motif, the Ets motif, the E-box motif and the thyroid transcription factor 2 ('TTF-2') motif. All of these IRSs mediate stimulatory effects of insulin on gene transcription. In contrast, an element with the consensus sequence T(G/A)TTT(T/G)(G/T), which we refer to as the phosphoenolpyruvate carboxykinase (PEPCK)-like motif, mediates the inhibitory effect of insulin on transcription of the genes encoding PEPCK, insulin-like-growth-factor-binding protein 1 (IGFBP-1), tyrosine aminotransferase and the glucose-6-phosphatase (G6Pase) catalytic subunit. The forkhead transcription factor FKHR has recently been shown to bind this PEPCK-like IRS motif and a model has been proposed in which insulin inhibits gene transcription by stimulating the phosphorylation and nuclear export of FKHR. Our results suggest that this model is consistent with the action of insulin on transcription of the gene encoding IGFBP-1 but not that of the G6Pase catalytic subunit. Thus, even though the IRSs in both promoters seem identical, they are functionally distinct. In addition, in the G6Pase catalytic subunit promoter, hepatocyte nuclear factor 1 ('HNF-1'), acts as an accessory factor to enhance the effect of insulin mediated through the IRS.

Glucose-6-phosphatase (G6Pase) is a multicomponent system located in the endoplasmic reticulum comprising a catalytic subunit and transporters for glucose-6-phosphate, inorganic phosphate, and glucose. We have recently cloned a novel gene that encodes an islet-specific G6Pase catalytic subunit-related protein (

Protein synthesis in mammalian cells is regulated through alterations in the states of phosphorylation of initiation and elongation factors (eIF's and eEF's), and of other regulatory proteins. This modulates their activities or their abilities to interact with one another. Insulin activates a number of these proteins including the guanine nucleotide-exchange factor eIF2B; the eIF4F complex, which (through eIF4E) interacts with the cap of the mRNA; p70 S6 kinase and elongation factor eEF2, which mediates the translation step of elongation. Control of the last three of these is linked to mTOR. In CHO cells, regulation of all these proteins by insulin is modulated by the presence of amino acids and/or glucose in the medium. For example, p70 S6 kinase activity declines in the absence of amino acids and cannot be stimulated by insulin under this condition. Readdition of amino acids, especially leucine, restores activity and insulin-sensitivity. In the case of eIF2B and eEF2, both amino acids and glucose must be provided in order for insulin to regulate their activities. In contrast, insulin-stirnulation of the formation of eIF4F complexes requires glucose, but not amino acids. Glucose metabolism is required for this permissive effect.Provision of substrates to mammalian tissues requires constant adaptations of metabolism to the quality and quantity of nutrients. Although it is well known that insulin has an important role in hepatic adaptations at the gene level, the molecular mechanisms involved are poorly understood. Recent findings have pointed to SREBP-lc (Sterol Regulatory Element Binding Protein -1c) as the transcription factor involved in insulin action. We have shown that SREBP-lc expression and nuclear abundance is positively regulated by insulin through a mechanism involving PL-kinase, and negatively by glucagon. Adenovirus-mediated ovcrexprcssion of a transcriptionally active form of SREBP-I c in cultured rat hepatocytes mimicks the inductive effects of insulin on glycolytic and lipogenic gene expression. A dominant negative form of SREBP-lc has the opposite effects. SREBP-lc mimicks also the negative effect of insulin since it is able to down-regulate the expression and the promoter activity of phosphoenolpyruvate carboxykinase in cultured hepatocytes. Injection of an adenovirus containing the active form of SREBP-lc to diabetic mice induces a rapid decrease of their hyperglycaemia and the predicted changes in hepatic gene expression. These studies point out to SREBP-lc as an important actor in the long term regulation of glucose homeostasis. ~1 7Insulin-Regulated Gene Expression.

It has recently been shown that adenoviral-mediated expression of peroxisome proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) in hepatocytes stimulates glucose-6-phosphatase catalytic subunit (G6Pase) gene expression. A combination of fusion gene, gel retardation and chromatin immunoprecipitation assays revealed that, in H4IIE cells, PGC-1 alpha mediates this stimulation through an evolutionarily conserved region of the G6Pase promoter that binds hepatocyte nuclear factor-4 alpha.

Streptomyces coelicolor A3(2) ftsI-and ftsW-null mutants produced aerial hyphae with no evidence of septation when grown on a traditional osmotically enhanced medium. This phenotype was partially suppressed when cultures were grown on media prepared without sucrose. We infer that functional FtsZ rings can form in ftsIand ftsW-null mutants under certain growth conditions. Rod-shaped bacteria that produce a peptidoglycan cell wall synthesize lateral-wall material during cell elongation and produce septa during cytokinesis. Most rod-shaped bacteria possess separate systems for these processes, each containing a protein of the SEDS (shape, elongation, division, and sporulation) family and a cognate class B penicillin-binding protein (PBP) (7, 9, 11). In Escherichia coli, the protein pairs involved in cell elongation and division are RodA-PBP2 and FtsW-FtsI (PBP3), respectively. However, some bacteria possess three protein pairs, as in Bacillus subtilis, where sporulation-specific division genes exist in addition to those for vegetative functions (15). Streptomyces coelicolor is a gram-positive, filamentous bacterium that requires cell division only for sporulation (13). Its genome possesses four homologous SEDS-PBP pairs (3).Here we report the characterization of S. coelicolor cell division genes ftsI and ftsW. We show that ftsI and ftsW are dispensable for colony formation but are required for efficient cell division. Similar to the ftsL and divIC mutants (2), the ftsIand ftsW-null mutants displayed medium-dependent phenotypic defects that are more severe on an osmotically enhanced medium. We suggest that because the ftsI and ftsW mutants are able to divide when grown on certain media, other proteins may compensate for the loss of FtsI and FtsW. Chains of spores are produced under certain growth conditions, implying that ladder-like arrays of Z rings (18) must be stably formed and function in the absence of FtsI and FtsW under certain conditions.Identification of ftsI and ftsW homologues in S. coelicolor. The S. coelicolor ftsI and ftsW homologues, ftsI Sc (StrepDB [http://streptomyces.org.uk/] accession number SCO2090) and ftsW Sc (accession number SCO2085), are located in the division and cell wall (dcw) cluster (Fig. 1). We determined the gene sequences prior to the S. coelicolor genome project. ftsI Sc is predicted to encode a 654-amino-acid, 69.5-kDa bitopic membrane protein with 26% (160/602) of its residues identical to B. subtilis PBP 2B (the FtsI homologue), 31% (188/604) identical to B. subtilis SpoVD (the sporulation-specific FtsI homologue), and 29% (175/586) identical to E. coli FtsI. ftsW Sc is predicted to encode a 456-amino-acid, 48-kDa integral membrane protein with 36% (128/351) of its residues identical to B. subtilis SpoVE (the sporulation-specific FtsW homologue), 36% (137/373) identical to B. subtilis FtsW (YlaO), and 31% (114/358) identical to E. coli FtsW. FtsW Sc lacks the unique C-terminal extension required for interaction with FtsZ in the related actinomycete Mycobacterium tuberculosis (...