Biomedical subjects

Leo A H Zeef

Publications and source records attributed to Leo A H Zeef.

5 recordsLinked to original sources

PubMed2006

Thioredoxin interacting protein is increased in sensory neurons in experimental diabetes.

Diabetic neuropathy is a major complication of diabetes and has multifactoral aetiology. The exact cause of damage is unknown although high glucose and oxidative stress are known to contribute significantly. In order to identify molecular targets of the disease and possibly new therapeutic targets, we previously examined the effect of diabetes on dorsal root ganglia (DRG) neurons using Affymetrix gene chip arrays. A number of individual genes and groups of genes were found to be dysregulated; the most significant of these was thioredoxin interacting protein (Txnip). This gene was found to have increased expression in DRG from diabetic rats with all durations of diabetes examined, including those that preceded the onset of functional changes such as decreased nerve conduction velocity. Increased Txnip expression therefore represents an early change in diabetic neuropathy that could, at least in part, be responsible for causing the initial functional deficits. This study confirmed the changes in Txnip expression at the mRNA and protein levels and identified the cell types responsible for the change. Furthermore we investigated the mechanism of diabetes-induced Txnip gene induction. Neither the antioxidant dexlipotam (R-lipoic acid) nor the p38 MAP kinase inhibitor SB239063 could prevent increases in Txnip expression despite reducing oxidative stress. However, treatment of rats with insulin prevented diabetes-induced increases in Txnip gene expression. These results indicate another mechanism by which diabetes may cause oxidative damage in peripheral nerve, and may represent a novel target for therapeutic intervention.

Animals↗

PubMed2005

Identification of novel genes in Arabidopsis involved in secondary cell wall formation using expression profiling and reverse genetics.

Forward genetic screens have led to the isolation of several genes involved in secondary cell wall formation. A variety of evidence, however, suggests that the list of genes identified is not exhaustive. To address this problem, microarray data have been generated from tissue undergoing secondary cell wall formation and used to identify genes that exhibit a similar expression pattern to the secondary cell wall-specific cellulose synthase genes IRREGULAR XYLEM1 (IRX1) and IRX3. Cross-referencing this analysis with publicly available microarray data resulted in the selection of 16 genes for reverse genetic analysis. Lines containing an insertion in seven of these genes exhibited a clear irx phenotype characteristic of a secondary cell wall defect. Only one line, containing an insertion in a member of the COBRA gene family, exhibited a large decrease in cellulose content. Five of the genes identified as being essential for secondary cell wall biosynthesis have not been previously characterized. These genes are likely to define entirely novel processes in secondary cell wall formation and illustrate the success of combining expression data with reverse genetics to address gene function.

3' Untranslated Regions↗

PubMed2004

The ETS domain transcription factor Elk-1 regulates the expression of its partner protein, SRF.

The ternary complex factors (TCF) are a subfamily of ETS domain transcription factors that bind and activate serum response elements (SREs) in the promoters of target genes in a ternary complex with a second transcription factor, serum response factor (SRF). Here, we have identified the SRF gene as a target for the TCFs, thereby providing a positive feedback loop whereby TCF activation leads to the enhancement of the expression of its partner protein SRF. The binding of the TCF Elk-1 to the SRF promoter and subsequent regulation of SRF expression occurs in a ternary complex-dependent manner. Our data therefore reveal that SRF is an important target for the ERK and Rho signaling pathways that converge on a ternary TCF-SRF complex at the SRE on the SRF promoter.

Base Sequence↗

PubMed2004

Ternary complex factor-serum response factor complex-regulated gene activity is required for cellular proliferation and inhibition of apoptotic cell death.

Members of the ternary complex factor (TCF) subfamily of the ETS-domain transcription factors are activated through phosphorylation by mitogen-activated protein kinases (MAPKs) in response to a variety of mitogenic and stress stimuli. The TCFs bind and activate serum response elements (SREs) in the promoters of target genes in a ternary complex with a second transcription factor, serum response factor (SRF). The association of TCFs with SREs within immediate-early gene promoters is suggestive of a role for the ternary TCF-SRF complex in promoting cell cycle entry and proliferation in response to mitogenic signaling. Here we have investigated the downstream gene regulatory and phenotypic effects of inhibiting the activity of genes regulated by TCFs by expressing a dominantly acting repressive form of the TCF, Elk-1. Inhibition of ternary complex activity leads to the downregulation of several immediate-early genes. Furthermore, blocking TCF-mediated gene expression leads to growth arrest and triggers apoptosis. By using mutant Elk-1 alleles, we demonstrated that these effects are via an SRF-dependent mechanism. The antiapoptotic gene Mcl-1 is identified as a key target for the TCF-SRF complex in this system. Thus, our data confirm a role for TCF-SRF-regulated gene activity in regulating proliferation and provide further evidence to indicate a role in protecting cells from apoptotic cell death.

Alleles↗

PubMed1998

A kirromycin-resistant EF-Tu species reverses streptomycin dependence of Escherichia coli strains mutated in ribosomal protein S12.

Streptomycin dependence can be caused by mutations in ribosomal protein S12. Mutations suppressing such streptomycin dependence have been found in ribosomal proteins S4 and S5, and in 16S rRNA. Here a new suppressor mutation localized in elongation factor Tu (EF-Tu) is described, consistent with recent models of ribosome-EF-Tu-tRNA interaction at the decoding centre. The EF-Tu mutation was obtained by genetic selection for streptomycin independence; it was identified as Ala375 --> Thr, previously described as EF-TuA(R) and known to confer a kirromycin-resistant, error-prone phenotype. Also, other streptomycin-dependent (SmD) S12 mutations could be complemented by this mutation. The streptomycin-independent (Sm1) strain grows more slowly than the wild-type (wt), suggesting that not all the defects of the S12 mutation can be complemented by EF-Tu[A375T]. Moreover, this strain is more susceptible than wt to reduction in the cellular EF-Tu concentration, and disruption of tufB led to considerable growth-rate impairment. Expression of EF-Tu from tufB, not only of wt EF-Tu and EF-Tu[A375T] but, remarkably, also of EF-Tu[G222D], known as EF-TuB0 and defective in protein synthesis, equally contributed to cell growth. In vitro analysis revealed a decreased translational activity of wt EF-Tu with SmD ribosomes as compared to EF-Tu[A375T], while EF-Tu[G222D] showed no activity at all, just as with wt ribosomes. Possible mechanisms are discussed for the improved growth rate observed in such Sm1 strains when they include wt EF-Tu or EF-Tu[G222D].

Anti-Bacterial Agents↗