Immunoreactive helix-destabilizing protein localized in transcriptionally active regions of Drosophila polytene chromosomes

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.

The elusive nuclear matrix

The structure of the interphase nucleus is a major area of current interest in cell biology. It is thought likely that the nucleus is organised around some form of structural matrix and that this matrix will play a role in processes as diverse as chromosome replication and the integration of gene expression. However, the structure of the matrix within the nucleus has remained elusive, largely because attempts to define it have been dogged by technical problems arising from the great complexity of this organelle. This situation is now being changed by the application of in situ analysis and of molecular genetic methodologies which are opening up this hitherto intractable field.

Phosphotyrosine-containing lactate dehydrogenase is restricted to the nuclei of PC12 pheochromocytoma cells

There are five lactate dehydrogenase (LDH) isoenzymes, composed of various combinations of two types of subunits. LDH-5, which contains only the LDH A subunit, is known to be present in both the cytoplasm and the nucleus, to act as a single-stranded DNA-binding protein possibly functioning in transcription and/or replication, and to undergo phosphorylation of tyrosine 238 in approximately 1% of the enzyme after cell transformation by certain tumor viruses. We have characterized LDH from wild-type PC12 pheochromocytoma cells and from a PC12 variant (MPT1) that exhibits altered lactate metabolism and altered expression of multiple genes. Wild-type and MPT1 cells contain different proportions of LDH isoenzymes, with LDH-5 being more predominant in wild-type cells than in the variant. A small fraction of LDH from PC12 cells contains phosphotyrosine. Approximately 99% of the total LDH activity is located in the cytoplasm, but all of the phosphotyrosine-containing LDH is located in the nucleus. Furthermore, essentially all of the nuclear LDH contains phosphotyrosine. These results suggest that tyrosine phosphorylation can affect its role in the nucleus.

Phosphotyrosine-containing lactate dehydrogenase is restricted to the nuclei of PC12 pheochromocytoma cells

There are five lactate dehydrogenase (LDH) isoenzymes, composed of various combinations of two types of subunits. LDH-5, which contains only the LDH A subunit, is known to be present in both the cytoplasm and the nucleus, to act as a single-stranded DNA-binding protein possibly functioning in transcription and/or replication, and to undergo phosphorylation of tyrosine 238 in approximately 1% of the enzyme after cell transformation by certain tumor viruses. We have characterized LDH from wild-type PC12 pheochromocytoma cells and from a PC12 variant (MPT1) that exhibits altered lactate metabolism and altered expression of multiple genes. Wild-type and MPT1 cells contain different proportions of LDH isoenzymes, with LDH-5 being more predominant in wild-type cells than in the variant. A small fraction of LDH from PC12 cells contains phosphotyrosine. Approximately 99% of the total LDH activity is located in the cytoplasm, but all of the phosphotyrosine-containing LDH is located in the nucleus. Furthermore, essentially all of the nuclear LDH contains phosphotyrosine. These results suggest that tyrosine phosphorylation can affect its role in the nucleus.

Interpreting the behavior of enzymes: purpose or pedigree?

To interpret the growing body of data describing the structural, physical, and chemical behaviors of biological macromolecules, some understanding must be developed to relate these behaviors to the evolutionary processes that created them. Behaviors that are the products of natural selection reflect biological function and offer clues to the underlying chemical principles. Nonselected behaviors reflect historical accident and random drift. This review considers experimental data relevant to distinguishing between nonfunctional and functional behaviors in biological macromolecules. In the first segment, tools are developed for building functional and historical models to explain macromolecular behavior. These tools are then used with recent experimental data to develop a general outline of the relationship between structure, behavior, and natural selection in proteins and nucleic acids. In segments published elsewhere, specific functional and historical models for three properties of enzymes--kinetics, stereospecificity, and specificity for cofactor structures--are examined. Functional models appear most suitable for explaining the kinetic behavior of proteins. A mixture of functional and historical models appears necessary to understand the stereospecificity of enzyme reactions. Specificity for cofactor structures appears best understood in light of purely historical models based on a hypothesis of an early form of life exclusively using RNA catalysis.

Lactate dehydrogenase and glyceraldehyde-phosphate dehydrogenase are single-stranded DNA-binding proteins that affect the DNA-polymerase-alpha-primase complex

Affinity chromatography on double-stranded (ds) and single-stranded (ss) DNA-cellulose columns was employed to find analogs of the Escherichia coli and T4 single-stranded DNA binding proteins (SSB proteins) in calf thymus. The interaction of several purified SSB proteins with the pure DNA-polymerase-alpha--primase complex on DNA synthesis on activated DNA and on primase-initiated M13 DNA served as a criterion for a possible involvement of one of these proteins in the process of DNA replication. Two SSB proteins were purified to essential homogeneity. These most abundant proteins exhibited apparent relative molecular masses of 35,000 (SSB-35) and 37,000 (SSB-37) for the protomers and 140,000 and 80,000 for the native enzymes. Both proteins resisted elution with 0.5 mg/ml dextran sulfate and were eluted from the ssDNA-cellulose with 0.2 M and 1 M NaCl, respectively. SSB-35 stimulated the DNA-polymerase-alpha--primase complex from the same organism up to fivefold over a broad range of DNA covering. By contrast, SSB-37 inhibited the primase-initiated replication of M13 DNA. Like most eukaryotic SSB proteins, these proteins showed a 300-fold preference for binding to ssDNA over dsDNA in a nitrocellulose filter binding assay, as well as strong binding to several DNA and RNA homopolymers. Furthermore, we provide evidence for a cooperative mode of binding for SSB-37. Although SSB-35 and SSB-37 behave as typically eukaryotic SSB proteins in all assays employed, we tested these SSB proteins for dehydrogenase activities as well. SSB-35 was found to be identical with lactate dehydrogenase and SSB-37 was identical with a dimeric form of glyceraldehyde-3-phosphate dehydrogenase. These results imply that further studies are mandatory in order to prove the authenticity of eukaryotic SSB proteins.

Identification of a nucleic acid helix-destabilizing protein from rat liver as lactate dehydrogenase-5

A rat liver DNA helix-destabilizing protein (HDP) that has previously been proposed to play a role in transcription has been identified as M chain lactate dehydrogenase (LDH-5; L-lactate:NAD+ oxidoreductase, EC 1.1.1.27). Tryptic peptides accounting for 157 amino acids in the rat liver HDP have been characterized and then matched to the published sequence for the M chain of porcine LDH. Based on amino acid compositions and direct solid-phase protein sequencing, at least 148 of the 157 residues that were compared are identical in both proteins. In addition, both porcine LDH and the rat liver HDP have blocked amino termini and similar amino acid compositions and molecular weights. Rat liver HDP and LDH-5 that were purified to molecular homogeneity had similar specific activities in both single-stranded DNA (ss DNA) binding and LDH assays. HPLC tryptic peptide maps were also identical for both the rat liver HDP and LDH proteins. Since preincubation of HDP in NADH prevents its binding to ss DNA, both NADH and ss DNA may be binding at the same site. Further support for this latter idea derives from chemical-modification studies which demonstrate that tyrosine-238, which is located near the coenzyme binding site of LDH, seems to be essential for the ability of HDP to bind ss DNA. These results indicate caution in ascribing in vivo roles solely on the basis of binding to ss DNA. Alternatively, they suggest that a single protein may play more than one biological role.

A destabilized DNA conformation associated with tightly bound nuclear proteins in active genes of rat myoblast

Purified nuclei from tissue cultured myoblasts were disrupted and centrifuged to equilibrium in a sarcosyl-caesium chloride gradient. A small portion (1.3% - 1.9%) of the non histone proteins (NHP) were banded with DNA in a high density region of the gradient. The DNA tightly bound to proteins representing about 0.6% of the total nuclear DNA was degraded after treating cell nuclei with S1 nuclease or DNAse I but resisted to mild micrococcal nuclease digestion. A large portion of the DNA sequences complementary to homologous RNA was concentrated in this DNA-proteins fraction. These finding suggest that a subset of NHP strongly associated to the active DNA regions play a role in the destabilisation of the double helical DNA during transcriptional processes.

Isolation of a mouse DNA fraction which encodes more informational than non informational RNA sequences

A small fraction of single-stranded DNA (ssDNA), amounting to 1.5--2% of the total DNA, was isolated from native nuclear DNA of mouse Ascites tumour cells. In RNA-driven annealing reactions, 40--42% of the ssDNA, (labelled with [3H]-thymidine or 125I) could be hybridized to cytoplasmic RNA was compared with 4--4.5% for the non repetitious component of bulk DNA and 60--63% of the ssDNA could be hybridized to nuclear RNA as compared with 20--22% for bulk DNA. It was also found that most of the ssDNA sequences which are hybridizable to homologous RNA, consisted of non self-reassociating DNA regions (which can be reassociated with non repetitious bulk DNA). These findings complete earlier data obtained in other cell systems and demonstrate that ssDNA mainly originates from active DNA transcription sites which encode informational RNA sequences. It is proposed that ssDNA is formed via selective endogenous nuclease attacks presumably at an early stage of the DNA purification procedure.

Manifold expression of new cellular genes in human lymphoid neoplasia

Previous studies performed in our laboratory have shown that a minor single-stranded DNA component (ssDNA) isolated from the bulk of double-stranded nuclear DNA (nDNA) of human, murine, or avian cells consisted mainly of active transcription sites. In the present work, ssDNA isolated from human lymphoid cells, either malignant or not, amounted to 1.2-1.4% of the total nDNA. This was labeled with 125I and utilized as a probe in RNA-driven iterative hybridization and cross-hybridization assays. In all cases of neoplasia studied, the same subfraction of ssDNA (equivalent to 10-12% of the total ssDNA) from malignant cells could be hybridized with cytoplasmic RNA from malignant cells, whatever their origin: acute lymphoid leukemia cells collected from blood of leukemic patients, local lymphosarcomas, or cells from two established strains grown in suspension, one Epstein-Barr virus positive (Raji strain), the other Epstein--Barr virus negative (Ramos strain). The majority of these tumor-specific DNA sequences could be reassociated with unique-copy DNA from both normal and malignant cells and were not expressed in normal lymphoid cells, including those of an established strain immortalized by Epstein--Barr virus and multiplied in culture. It is concluded that a great number of new transcription units, in the range of 2500-3000 per cell genome, were activated after spontaneous malignant transformation of lymphoid cells.