Developmental and metabolic regulation of the Drosophila melanogaster 3-hydroxy-3-methylglutaryl coenzyme A reductase.

Abstract

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase in Drosophila melanogaster synthesizes mevalonate for the production of nonsterol isoprenoids, which are essential for growth and differentiation. To (Mr, 98,165) that was similar to the hamster HMG CoA reductase. The C-terminal region had 56% identical residues and the N-terminal region had 7 potential transmembrane domains with 32 to 60% identical residues. In hamster HMG CoA reductase, the membrane regions were essential for posttranslational regulation. Since the Drosophila enzyme is not regulated by sterols, the strong N-terminal similarity was surprising. Two HMG CoA reductase mRNA transcripts, -3.2 and 4 kilobases, were differentially expressed throughout Drosophila development. Mevalonate-fed Schneider cells showed a parallel reduction of both enzyme activity and abundance of the 4-kilobase mRNA transcript.Cholesterol is important for structural purposes in the membranes of vertebrates, but recent studies have also elucidated its role in regulating the expression of certain genes (5). The rate-controlling enzyme for cholesterol synthesis, 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, is regulated by cholesterol in a complex pattern with both transcriptional (28, 34) and posttranslational (8, 19) mechanisms. As a typical housekeeping gene, the HMG CoA reductase gene is usually transcriptionally active. Its steady-state activity is subject to multivalent feedback suppression (4) by at least two classes of metabolic products derived from its immediate product, mevalonate. Cholesterol, the major mevalonate-derived product of mammalian cells, suppresses both HMG CoA reductase activity and its mRNA levels in cultured cells (10) and rat liver (26). Pretreatment of cells with cholesterol also prevented transcription from the gene in isolated nuclei (28), and the hamster HMG CoA reductase promoter remained cholesterol sensitive when transfected into cultured cells (34). Posttranslational regulation was revealed by the accelerated degradation of the enzyme in response to exogenous cholesterol (8). Thus, cholesterol has regulatory effects in both the nucleus and cytoplasm.Owing to the rapid and high conversion of mevalonate to sterols in mammals, it has been difficult to assess the sterol-independent regulatory pathway of HMG CoA reductase. Studies of this pathway suggested that the basal regulation was mediated by unidentified nonsterol mevalonate derivatives (16,47 Like the mammalian enzyme, the HMG CoA reductase of cultured Drosophila cells (Kc and Schneider cells) appears to be a microsomal enzyme whose activity is modulated by the addition of exogenous mevalonate. In contrast to the hamster enzyme, exogenous sterols have no effect upon the Drosophila HMG CoA reductase (3,32,43) and thus allow a clear separation of the sterol and nonsterol regulatory pathways. Since insects lack the ability to synthesize sterols and their HMG CoA reductase is insensitive to sterol regulation, one might conclude that insects either lost or neve...

Isolation and Characterization of cDNAs Encoding Wheat 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase

“…The first section at the base of the leaf is the youngest, and the tip section is the oldest (Fig. 8) (Caelles et al, 1989;Learned and Fink, 1989), tomato (Narita and Gruissem, 1989), human (Luskey and Stevens, 1985), yeast (Basson et al, 1988), and Drosophila (Gertler et al, 1988). Relative to the wheat sequence, identical or conserved residues are shown in gray and residues that are neither identical nor conserved are shown in white.…”

“…The degree of sequence homology among the three cDNAs is very high, as indicated by the shading. Figure 3 shows sequence homology comparison among HMGR genes by computer alignment of the translated wheat HMGR 18 partial cDNA sequence with that from Arabidopsis (Caelles et al, 1989;Learned and Fink, 1989), tomato (Narita and Gruissem, 1989;Narita et al, 1991), human (Luskey and Stevens, 1985), yeast (Basson et al, 1988), and Drosophila (Gertler et al, 1988).…”

“…cDNAs and genomic HMGR clones have been isolated from Drosophila (Gertler et al, 1988), yeast (Basson et al, 1988), sea urchin (Woodward et al, 1988), hamster (Chin et al, 1984), and human (Luskey and Stevens, 1985). Recently, with the use of hamster and yeast probes plant HMGR cDNAs and genomic clones have been isolated from Arabidopsis (Caelles et al, 1989;Leamed and Fink, 1989), tomato (Narita and Gruissem, 1989;Narita et al, 1991), and Hevea (Chye et al, 1991).…”

Molecular cloning, developmental pattern and tissue expression of 3‐hydroxy‐3‐methylglutaryl coenzyme A reductase of the cockroach Blattella germanica

“…Therefore, it is unlikely that this structural similarity in the transmembrane regions has been maintained only to provide sensitivity to sterol-mediated degradation. Since mevalonate affects the overall protein level, decreasing synthesis and increasing the rate of HMG-CoA reductase degradation [39,401, it has been suggested that conservation of these domains may be essential for recognizing specific mevalonate derivatives or their binding proteins [5]. Indeed, Simoni and coworkers showed that the and cholesterol-triggered degradation [42].…”

“…At present, the primary structure of HMG-CoA reductase is known for a variety of eukaryotic organisms, including mammals [23- [5]. The comparison of B. germanica HMGCoA reductase with those of these species reveals extensive conservation, especially in the catalytic domain, which is located in the C-terminal region (44 -66 % identical amino acid residues).…”