Isolation and sequencing of a cDNA encoding the B isozyme of rat phosphoglycerate mutase

Effects of thyroid hormone and hypoxia on 2,3-bisphosphoglycerate, bisphosphoglycerate synthase and phosphoglycerate mutase in rabbit erythroblasts and reticulocytes in vivo

OBJECTIVES

The effects of triiodothyronine (T(3)) and hypoxia on 2,3-bisphosphoglycerate (2,3-BPG) studied in vitro are unclear. To clarify these effects we selected a more physiologic approach: the in vivo study in rabbits. We also present the changes produced by T(3) and hypoxia on phosphoglycerate mutase (PGAM), which requires 2,3-BPG as a cofactor, and 2,3-BPG synthase (BPGS), the enzyme responsible for 2,3-BPG synthesis in erythroblasts and reticulocytes.

METHODS

Hyperthyroidism was induced by daily T(3) injection (250 microg/kg), hypoxia by a mixture of 90% nitrogen and 10% oxygen and hypothyroidism by propylthiouracil (PTU) added to drinking water.

RESULTS

Both T(3) administration and hypoxic conditions increased 2,3-BPG levels and BPGS mRNA levels and activity in erythroblasts but not in reticulocytes. Unlike BPGS, both PGAM mRNA levels and activity were increased in erythroblasts and reticulocytes under hyperthyrodism and hypoxia. The antihormone PTU produced opposite effects to T(3).

CONCLUSION

The results presented here suggest that both hyperthyroidism and hypoxia modulate in vivo red cell 2,3-BPG content by changes in the expression of BPGS. Similarly, the changes in PGAM activity are also explained by changes in its expression.

Effects of hypoxia and thyroid hormone on mRNA levels and activity of phosphoglycerate mutase in rabbit tissues

AIM

In the present work, we studied the effects of hypoxia and triiodothyronine (T(3)) on phosphoglycerate mutase (PGAM) activity and expression in rabbit liver, brain, and skeletal muscle under in vivo conditions.

METHODS

Hypoxia was induced in a methacrylate cage with a mixture of 90% nitrogen and 10% oxygen. Hyperthyroidism was induced daily by T(3) injection (250 microg/kg).

RESULTS

Hypoxia increases the PGAM activity in liver and brain, tissues which possess type PGAM-BB isozyme, but does not affect the PGAM activity in muscle which possesses type PGAM-MM isozyme. T(3) administration increases the PGAM activity in muscle and liver, but does not affect the enzyme activity in the brain. In all cases, the activity changes in parallel with those of PGAM mRNA levels.

CONCLUSION

The tissue-specific effects of hypoxia and T(3) could be explained by the tissue-specific distribution of both PGAM isozyme and T(3) receptors.

Effects of thyroid hormone on mRNAs of phosphoglycerate mutase subunits in rat muscle during development

BACKGROUND

We previously showed that triiodothyronine (T3) stimulates muscle phosphoglycerate mutase (PGAM) activity and isozyme transition in rat skeletal and cardiac muscles.

METHODS

The effects of T3 on PGAM types B and M subunit expression in rat muscle during development are reported.

RESULTS

T3 administration during the first 21 days of rat life more than doubles type M PGAM mRNA levels, but produces minor effects on type B PGAM mRNA levels. The antihormone propylthiouracil (PTU) slightly decreases both type B and M mRNA levels, but this decrease is not statistically significant.

CONCLUSION

Thyroid hormone influences PGAM mRNA isozyme levels differently and increases type M mRNA.

2,3-Bisphosphoglycerate-independent phosphoglycerate mutase is conserved among different phylogenic kingdoms

We have previously demonstrated that maize (Zea mays) 2,3-bisphosphoglycerate-independent phosphoglycerate mutase (PGAM-i) is not related to 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase. With the aid of specific anti-maize PGAM-i antibodies, we demonstrate here the presence of a closely related PGAM-i in other plants. We also describe the isolation and sequencing of a cDNA-encoding almond (Prunus amygdalus) PGAM-i that further demonstrates this relationship among plant PGAM-i. A search of the major databases for related sequences allowed us to identify some novel PGAM-i from different sources: plants (Arabidopsis thaliana, Oryza sativa and Antithamniom sp.), monera (Escherichia coli, Bacillus subtilis and Bacillus megaterium) and animals (Caenorhabditis elegans). All of these amino acid sequences share a high degree of homology with plant PGAM-i. These observations suggest that the PGAM-i from several biological kingdoms constitute a family of protein different from other proteins with related enzymatic function and arose from a common ancestral gene that has diverged throughout its evolution.

The muscle-specific phosphoglycerate mutase gene is specifically expressed in testis during spermatogenesis

Spermatogenesis is a dramatic differentiation process which involves very selective but poorly characterized gene-expression patterns. To gain insight into this process, we have investigated the expression during spermatogenesis of the genes that encode phosphoglycerate mutase, an essential glycolytic enzyme for the spermatozoa energy supply. By using cDNA and genomic probes we demonstrate the presence in testis of a mRNA corresponding to the muscle-specific phosphoglycerate mutase which shows a longer poly(A) tail. This muscle-specific gene is submitted to developmental regulation during testis maturation and begins to be expressed at postnatal day 22, when germ cells start to enter into meiosis. Northern blot and in situ hybridization experiments show that in contrast to what happens during skeletal-muscle differentiation, PGAM-M gene expression during spermatogenesis is not coupled to constitutive phosphoglycerate mutase (PGAM-B) gene repression. Thus, the muscle-specific PGAM-M gene constitutes a meiotic gene and therefore represents a very interesting model to study differential tissue-specific gene expression.

Molecular genetic studies in muscle phosphoglycerate mutase (PGAM-M) deficiency

Phosphoglycerate mutase (PGAM; EC 2.7.5.3) catalyzes the interconversion of 2-phosphoglycerate and 3-phosphoglycerate in the glycolytic pathway. Hereditary muscle PGAM deficiency has been identified in 9 patients with myopathy. All patients had exercise intolerance and 6 had myoglobinuria. Seven of the 9 patients were African-Americans: 5 of them were homozygous for a nonsense mutation, TGG(Trp) to TAG at codon 78; 1 was a compound heterozygote for the nonsense mutation and a missense mutation, GAG(Glu) to GCG(Ala) at codon 89; and 1 could not be tested. The only 2 Caucasian patients, a brother and sister, were homozygous for a different missense mutation, CGG(Arg) to TGG(Trp) at codon 90. Despite the small number of patients identified, these findings indicate that there is a common mutation in African-Americans while there may be molecular genetic heterogeneity in other ethnic groups.

The gene encoding rat phosphoglycerate mutase subunit M: cloning and promoter analysis in skeletal muscle cells

The expression of the gene encoding the muscle-specific (M)-subunit of phosphoglycerate mutase (PGAM-M) is restricted to adult skeletal and cardiac muscle. In order to study its expression in muscle, the rat PGAM-M gene has been isolated and sequenced. Rat PGAM-M spans about 2.2 kb and is composed of three exons: 442, 181 and 186-bp long, and two introns of 97 bp and 1.3 bp. The analysis of the 5'-flanking region reveals a promoter which contains multiple DNA regulatory elements and constitutes an ideal model to study muscle gene transcriptional regulation. Thus, the elements responsible for rat PGAM-M muscle-specific expression have been identified by transient transfection in chicken embryo primary cultures, using chimeric constructs of the rat promoter linked to a cat reporter gene. Here, we report that in spite of the abundance of E-box motifs in the rat PGAM-M promoter known for their involvement in muscle gene expression, two DNA elements regulate the muscle-specific transcription of rat PGAM-M: an A/T motif, the putative MEF-2-binding site (myocyte-specific enhancer-binding factor 2), and a proximal 27-bp element which is conserved between the rat and human genes. These two elements define a small promoter (170 bp) sufficient to support potent and skeletal-muscle-specific expression. The conserved 27-bp region contains a transcriptional regulatory element able to confer muscle-specific expression when located upstream from a heterologous TATA box.

Thyroid hormone stimulates phosphoglycerate mutase activity and isozyme transition in rat muscle tissues

Triiodothyronine (T3) increases phosphoglycerate mutase (PGAM) specific activity in rat skeletal and cardiac muscles. This increase is concomitant with an increase in the proportion of phosphoglycerate mutase isozymes which contain type-M subunit. Propylthiouracil (PTU), an anti-hormone, not only decreases phosphoglycerate mutase activity with respect to control rats, but also decreases the total M subunit contents. In liver, which only possesses type-B subunit phosphoglycerate mutase, none of the effects were detected.