Cloning and prokaryotic expression of a biologically active human placental aldose reductase

Role of aldo-keto reductase enzymes in mediating the timing of parturition

A better understanding of the mechanisms underlying parturition would provide an important step toward improving therapies for the prevention of preterm labor. Aldo–keto reductases (AKR) from the 1D, 1C, and 1B subfamilies likely contribute to determining the timing of parturition through metabolism of progesterone and prostaglandins. Placental AKR1D1 (human 5β reductase) likely contributes to the maintenance of pregnancy through the formation of 5β-dihydroprogesterone (DHP). AKR1C1, AKR1C2, and AKR1C3 catalyze the 20-ketosteroid and 3-ketosteroid reduction of progestins. They could therefore eliminate tocolytic progestins at term. Activation of the F prostanoid receptor by its ligands also plays a critical role in initiation of labor. AKR1C3 and AKR1B1 have prostaglandin (PG) F synthase activities that likely contribute to the initiation of labor. AKR1C3 converts PGH₂ to PGF_2α and PGD₂ to 9α,11β-PGF₂. AKR1B1 also reduces PGH₂ to PGF_2α, but does not form 9α,11β-PGF₂. Consistent with the potential role for AKR1C3 in the initiation of parturition, indomethacin, which is a potent and isoform selective inhibitor of AKR1C3, has long been used for tocolysis.

Urine and plasma galactitol in patients with galactose-1-phosphate uridyltransferase deficiency galactosemia

Urinary excretion of galactitol was determined in 95 normals (N/N), 67 galactosemic (G/G), and 39 compound heterozygotes for the Duarte and galactosemia genotype (D/G). Galactitol excretion is age-dependent in both normal individuals and patients with classic galactosemia on lactose-restricted diets. In galactosemic patients who are homozygous for the Q188R mutation, urinary galactitol levels were fivefold to 10-fold higher than those of normal subjects of comparable age. All but a few patients with classic galactosemia with the Q188R mutation and another mutant G allele had urinary excretion comparable to the Q188R homozygous patients. African-American galactosemic patients with the S135L mutation of the galactose-1-phosphate uridyltransferase (GALT) gene also excreted abnormal quantities of galactitol. Most subjects with a Duarte allele and a G allele excrete normal amounts of the sugar alcohol. There is a correlation between galactitol excretion and red blood cell (RBC) galactose-1-phosphate (gal-1-P). Plasma galactitol was also elevated in galactosemic patients (3.4 to 23.2 micromol/L; undetectable in normal individuals). In contrast to the decrease in urinary galactitol with age, plasma levels remain in a narrow concentration range with no significant difference with age. Urine and plasma galactitol distinguish galactosemic patients from normals. In addition, urinary galactitol excretion may be an important parameter for the assessment of steady-state galactose metabolism in galactosemia.

Further characterization of a rat hepatoma-derived aldose-reductase-like protein--organ distribution and modulation in vitro

A protein detected in N-methyl-N-nitrosourea-initiated rat hepatomas by two-dimensional electrophoresis at 35 kDa/pI 7.4 was identified in a previous study by internal amino acid micro sequencing as an aldose-reductase-like protein [Zeindl-Eberhart, E., Jungblut, P. R., Otto, A. & Rabes, H. M. (1994) Identification of tumor-associated protein variants during rat hepatocarcinogenesis, J. Biol. Chem. 269, 14589-14594]. Two-dimensional electrophoresis of rat lens proteins revealed a spot at 37 kDa/pI 6.8 that showed a high degree of identity (98.5%) with rat lens aldose reductase after amino acid sequencing and 80% sequence identity to the rat-hepatoma-derived aldose-reductase-like protein. This suggests that hepatoma-derived aldose-reductase-like protein and rat lens aldose reductase are related proteins encoded by different genes. A different expression profile of these proteins was found in various rat organs. Rat lens aldose reductase is present, in addition to in lens, in heart, brain, muscle, lung, duodenum, kidney, spleen and bone marrow, while the hepatoma-derived aldose-reductase-like protein is found preferentially in hepatomas and in embryonic liver. Though different in organ expression, an identical response was found for both proteins after stimulation with fibroblast growth factor-1 and after exposure to increased glucose concentrations. Since rat hepatoma-derived aldose-reductase-like protein is expressed in embryonic, but not in adult liver, it is assumed that it is expressed in hepatomas as a functionally active embryonal type of aldose reductase during hepatocarcinogenesis. Immunohistochemistry revealed that the hepatoma-derived aldose-reductase-like protein is expressed already in the preneoplastic stage of hepatocarcinogenesis and might potentially serve as a marker enzyme in early hepatic neoplasia.

The role of polyols in the pathophysiology of hypergalactosemia

Cellular accumulation of galactitol has been suggested to cause the apparent dietary-independent, long-term complications in classic galactosemia. Experimental animals rendered hypergalactosemic by galactose feeding accumulate tissue galactitol, as well as millimolar quantities of galactose, and manifest biochemical, physiological and pathological abnormalities which are generally eliminated or curtailed by the concomitant administration of an aldose reductase inhibitor. This includes reduced cellular content of the cyclic polyol, myo-inositol, which like galactitol may function as an alternate intracellular osmolyte. However, the abnormalities detected in experimental galactosemic animals are more compatible with findings in experimental diabetes mellitus than in human galactosemia. Because patients with galactokinase deficiency fail to manifest the CNS and ovarian complications which characterize classic galactosemia, yet during long-term lactose restriction excrete comparable urinary quantities of galactitol, this polyol alone is not likely to play an important role during postnatal life in the pathogenesis of long-term complications. Notwithstanding, a role for either galactitol or myo-inositol in an intrauterine toxicity cannot be dismissed.

A human aldehyde dehydrogenase (aldose reductase) pseudogene: nucleotide sequence analysis and assignment to chromosome 3

Four cosmid clones containing putative pseudogenes for human aldehyde dehydrogenase (Aldose reductase) were isolated from libraries made to two individuals. These clones show different patterns on digestion with restriction endonucleases and probably represent distinct and separate loci. The DNA sequence of one of the putative pseudogenes (cosmid AR.F) was determined, and comparisons demonstrate 89.7% homology with the cDNA sequence of the functional aldose reductase gene. This pseudogene sequence contains no intronic sequences, whereas the functional aldose reductase has nine introns. In addition, the homology disappears in region 5' to the transcription start site for the cDNA, implying that regulatory elements such as the promoter are missing from this pseudogene. The pseudogene defined by cosmid AR.F has been mapped to chromosome 3 by polymerase chain reaction using amplimers specific for this pseudogene to amplify DNA from somatic cell hybrids.

Tac promoter vectors incorporating the bacteriophage T7 gene 10 translational enhancer sequence for improved expression of cloned genes in Escherichia coli

Two new plasmid expression vectors, pTacT7 and pTacT7L, have been constructed, which incorporate between the tac promoter and a downstream NcoI-HindIII polylinker sequence a synthetic sequence derived from the region upstream from gene 10 of bacteriophage T7 (g10-L). This sequence was recently shown to act as a translational enhancer (Olins et al., 1988) and was termed "Epsilon" (Enhancer of Protein Synthesis Initiation) element (Olins and Rangwala, 1989). In this communication we describe in detail the construction of ptacT7 and ptacT7L. Furthermore, we present evidence that the "Epsilon" element is able to enhance 3 to 20-fold the expression levels of two poorly expressed test genes encoding the human placental proteins PP9 and PP15. On the other hand, the expression levels of two highly expressed test genes encoding the human placental proteins PP4 and FXIIIa could not be further enhanced by the presence of the "Epsilon" element. These experiments show that the T7 gene 10 leader sequence can be utilized to improve the expression yields of otherwise poorly expressed heterologous genes in Escherichia coli.

Immunochemically detected placental proteins and their biological functions

During the last 20 years a systematic search for proteins occurring in human term placenta (afterbirth) has been performed in our laboratory. As a result more than 30 soluble placental proteins and at least 20 different solubilized antigens apparently derived from the placental membranes have been identified by immunochemical methods in extracts from human term placentas. Most of these proteins have already been isolated to purity and characterized by their physicochemical parameters. Specific antisera to these proteins were obtained by immunizing animals with the corresponding purified proteins. They were used detect and localize these antigens by immunochemical methods in the placenta and in other human tissues. Sensitive immunochemical assays have been developed to exactly quantitate the new proteins in body fluids and to find out the diagnostic significance of measurement of these proteins in pregnant women and in patients with tumors and other diseases. Another aim was to elucidate the biological functions of our immunochemically detected proteins. The results obtained thus far are reported.