A major single-stranded DNA binding protein from ovaries of the frog, Xenopus laevis, is lactate dehydrogenase

Inhibition of lactate dehydrogenase activity as an approach to cancer therapy

In the attempt of developing innovative anticancer treatments, growing interest has recently focused on the peculiar metabolic properties of cancer cells. In this context, LDH, which converts pyruvate to lactate at the end of glycolysis, is emerging as one of the most interesting molecular targets for the development of new inhibitors. In fact, because LDH activity is not needed for pyruvate metabolism through the TCA cycle, inhibitors of this enzyme should spare glucose metabolism of normal non-proliferating cells, which usually completely degrade the glucose molecule to CO2. This review is aimed at summarizing the available data on LDH biology in normal and neoplastic cells, which support the anticancer therapeutic approach based on LDH inhibition. These data encouraged pharmaceutical industries and academic institutions in the search of small-molecule inhibitors and promising candidates have recently been identified. The availability of inhibitors with drug-like properties will allow the evaluation in the near future of the real potential of LDH inhibition in anticancer treatment, also making the identification of the most responsive neoplastic conditions possible.

Lactate dehydrogenase enhances immunoglobulin production by human hybridoma and human peripheral blood lymphocytes

Lactate dehydrogenase (LDH) derived from rabbit muscle enhanced IgM production by human-human hybridoma HB4C5 cells 12.4-fold at 320 mug/ml under serum-free conditions. LDHs from pig muscle and pig heart also accelerated IgM production 8.4- and 6.4-fold, respectively. The immunoglobulin production stimulating activity of LDH was not accompanied by activation of cell proliferation. LDH from rabbit muscle facilitated IgM and IgG production by human peripheral blood lymphocytes. This means LDH stimulates immunoglobulin production not only by the specified hybridoma cell line, but also by unspecified immunoglobulin producers. LDH from rabbit muscle enhanced IgM production of transcription-suppressed HB4C5 cells treated with actinomycin D. The immunoglobulin production-stimulating factors (IPSFs) effect of LDH was slightly weakened by sodium fluoride (translation inhibitor) treatment of HB4C5. Moreover, the amount of intracellular IgM of monensin-treated HB4C5 cells was obviously enhanced by LDH. This result means that the IPSF effect of LDH is irrelevant to the post-translation activity of target cells. It is expected from these findings that LDH from rabbit muscle accelerates the translation step to enhance immunoglobulin productivity. The immunoglobulin production-stimulating activity of LDH was inhibited by colchicine, endocytosis inhibitor. This fact suggests that it is necessary for LDH to be taken by target cells to act as an IPSF.

Detection of proteins binding to short RNA.DNA hybrids or short antisense oligonucleotides in Xenopus laevis oocytes and human macrophage cell extracts by photoaffinity radiolabeling

Using a 12 base pair RNA.DNA hybrid, substituted with bromouracil on either the RNA or DNA strand, we have detected by photoaffinity radiolabeling a limited set of proteins able to bind to RNA.DNA hybrids in both Xenopus oocyte extracts and human macrophage extracts. Resulting patterns of crosslinked proteins were highly dependent on the strand (DNA or RNA) that was substituted. With one exception, none of the proteins investigated in competition experiments was found to be absolutely specific for RNA.DNA hybrids, as at least one other nucleic acid, either single-stranded DNA or single-stranded RNA, was found to compete efficiently. None of the proteins detected in this assay correspond to the size expected for RNases H. Using the same methodology, we have detected proteins that bind to short oligodeoxyribonucleotides. Although we have essentially detected in Xenopus oocytes one prominent protein of approximately 75 kDa, corresponding to replication protein A (RPA) whatever the oligonucleotide used, the patterns obtained with extracts of human macrophages were more complex and dependent on the oligonucleotide used. If a protein corresponding to RPA was observed most of the time, other crosslinks of similar or sometimes higher intensity were also detected. Interestingly, among these, one protein of 35 kDa appears paradoxically to bind and crosslink to a dodecamer but not to an octadecamer containing the same sequence placed either at its 3'-end or 5'-end.

The 40 kDa 63Ni(2+)-binding protein (pNiXc) on western blots of Xenopus laevis oocytes and embryos is the monomer of fructose-1,6-bisphosphate aldolase A

A Ni(2+)-binding protein (pNiXc, 40 kDa), present in Xenopus laevis oocytes and embryos, was isolated from mature oocytes by chromatography on DEAE-cellulose and cellulose phosphate, followed by FPLC on Ni-iminodiacetate-Agarose, or reverse-phase HPLC on a C-4 column. Size-exclusion HPLC showed that intact pNiXc is approximately 155 kDa, consistent with tetrameric structure. After cleavage with Lys-C proteinase or cyanogen bromide, six peptides were separated by HPLC and sequenced by Edman degradation, providing sequence data for 83 residues. Data-base search showed similarity of pNiXc to eukaryotic aldolases, with 96% identity to human aldolase A. pNiXc demonstrated aldolase activity with fructose 1,6-bisphosphate as substrate (Km, 30 microM Vmax 26 mumol min-1 mg-1); the aldolase activity was inhibited non-competitively by Cu2+, Cd2+, Co2+, or Ni2+. Equilibrium dialysis showed high affinity binding (Kd, 7 microM) of 1 mole of Ni per mole of 40 kDa subunit. Based on metal-blot competition assays, the abilities of metals to compete with 63Ni2+ for binding to pNiXc were ranked: Cu2+ >> Zn2+ > Cd2+ > Co2+. This study identifies pNiXc as the monomer of fructose-1,6-bisphosphate aldolase A, and raises the possibility that aldolase A is a target enzyme for metal toxicity.

Expression of mitochondrial genes and DNA-repair-related nuclear genes is altered in xeroderma pigmentosum fibroblasts

Differential hybridization was used to detect repair defects in xeroderma pigmentosum (XP) that are not amenable to current analyses. cDNA libraries were constructed from cytoplasmic RNA of normal and XP fibroblast strains (complementation groups A and D) and analyzed for differential gene expression. More than 40,000 lambda gt10 cDNA clones were differentially screened with in vitro transcripts made from cDNA in the pBluescript vector. Six differential clones were detected in the libraries of the XP group A and D strains which caused stronger or weaker signals when probed with transcripts from XP strains than with those from the normal strains. Two clones coded for mitochondrial genes: mitochondrial 16 S rRNA and ATPase 6L. Overexpression of mitochondrial genes in XP may indicate that functions of the ATP-generating system are impaired since such functions are intensified whenever they become insufficient, for example as a consequence of DNA damage. It is tempting to assume that abnormal mitochondria are one of the causes for the neurological malfunctions in XP. Furthermore, densitometric analysis of Northern blots revealed that mRNA of lactate dehydrogenase, chain M, was less abundant in four XP group A strains (extent of reduction: 70%) and in two XP group D strains (extent of reduction: 58%). Enzyme activity was also diminished. In addition, mRNA of the gene for glyceraldehyde-3-phosphate dehydrogenase was less expressed in the same XP group A and D fibroblast strains investigated (reduction in both complementation groups: 50%). Both glycolytic enzymes have nuclear functions apart from their role in sugar metabolism. Lactate dehydrogenase, chain M, is identical to a helix-destabilizing protein; it is closely associated with chromatin and unfolded DNA, suggesting a role in DNA synthesis and transcription. The 37-kDa subunit of glyceraldehyde-3-phosphate dehydrogenase is involved in transcription and was shown to be identical to uracil-DNA glycosylase, a base-excision repair enzyme. We presume that the nuclear functions of these glycolytic enzymes may be thwarted in the XP strains investigated and may account for malfunctions in XP, particularly for neurological disturbances.