The CpG-rich promoter of human LDH-C is differentially methylated in expressing and nonexpressing tissues

DNA methylation profiling of myelodysplastic syndromes and clinical response to azacitidine: A multicentre retrospective study

Real-world data have revealed that a substantial portion of patients with myelodysplastic syndromes (MDS) does not respond to epigenetic therapy with hypomethylating agents (HMAs). The cellular and molecular reasons for this resistance to the demethylating agent and biomarkers that would be able to predict the treatment refractoriness are largely unknown. In this study, we shed light on this enigma by characterizing the epigenomic profiles of patients with MDS treated with azacitidine. Our approach provides a comprehensive view of the evolving DNA methylation architecture of the disease and holds great potential for advancing our understanding of MDS treatment responses to HMAs.

Structural and functional regulation of lactate dehydrogenase-A in cancer

Dysregulated metabolism is one of the hallmarks of cancer. Under normal physiological conditions, ATP is primarily generated by oxidative phosphorylation. Cancers commonly undergo a dramatic shift toward glycolysis, despite the presence of oxygen. This phenomenon is known as the Warburg effect, and requires the activity of LDHA. LDHA converts pyruvate to lactate in the final step of glycolysis and is often upregulated in cancer. LDHA inhibitors present a promising therapeutic option, as LDHA blockade leads to apoptosis in cancer cells. Despite this, existing LDHA inhibitors have shown limited clinical efficacy. Here, we review recent progress in LDHA structure, function and regulation as well as strategies to target this critical enzyme.

Methylation-dependent and independent regulatory regions in the Na,K-ATPase alpha4 (Atp1a4) gene may impact its testis-specific expression

The α4 Na,K-ATPase is a sperm-specific protein essential for sperm motility and fertility yet little is known about the mechanisms that regulate its expression in germ cells. Here, the potential involvement of DNA methylation in regulating the expression of this sperm-specific protein is explored. A single, intragenic CpG island (Mα4-CGI) was identified in the gene encoding the mouse α4 Na,K-ATPase (Atp1a4), which displayed reduced methylation in mouse sperm (cells that contain α4) compared to mouse kidney (tissue that lacks α4 expression). Unlike the intragenic CGI, the putative promoter (the -700 to +200 region relative to the transcriptional start site) of Atp1a4 did not show differential methylation between kidney and sperm nevertheless it did drive methylation-dependent reporter gene expression in the male germ cell line GC-1spg. Furthermore, treatment of GC-1spg cells with 5-aza2-deoxycytidine led to upregulation of the α4 transcript and decreased methylation of both the Atp1a4 promoter and the Mα4-CGI. In addition, Atp1a4 expression in mouse embryonic stem cells deficient in DNA methyltransferases suggests that both maintenance and de novo methylation are involved in regulating its expression. In an attempt to define the regulatory function of the Mα4-CGI, possible roles of the Mα4-CGI in regulating Atp1a4 expression via methylation-dependent transcriptional elongation inhibition in somatic cells and via its ability to repress promoter activity in germ cells were uncovered. In all, our data suggests that both the promoter and the intragenic CGI could combine to provide multiple modes of regulation for optimizing the Atp1a4 expression level in a cell type-specific manner.

Testis-specific lactate dehydrogenase is expressed in somatic tissues of plateau pikas

LDH-C₄ is a lactate dehydrogenase that catalyzes the interconversion of pyruvate with lactate. In mammals the, Ldh-c gene was originally thought to be expressed only in testis and spermatozoa. Plateau pika (Ochotona curzoniae), belonging to the genus Ochotona of the Ochotonidea family, is a hypoxia tolerant mammal living at 3000–5000 m above sea levelon the Qinghai-Tibet Plateau. We found that the expression pattern of six LDH isoenzymes in the somatic tissues of female and male plateau pikas to be the same as those in testis and sperm, suggesting that LDH-C₄ was expressed in somatic tissues of plateau pika. Here we report the detection of LDHC in the somatic tissues of plateau pika using RT-PCR, Western blotting and immunohistochemistry. Our results indicate that Ldh-c mRNA is transcribed in the heart, liver, lung, kidney, brain, skeletal muscle and testis. In somatic tissues LDHC was translated in the cytoplasm, while in testis it was expressed in both cytoplasm and mitochondria. The third band from cathode to anode in LDH isoenzymes was identified as LDH-C₄. The finding that Ldh-c is expressed in both somatic tissues and testis of plateau pika provides important implications for more in-depth research into the Ldh-c function in mammals.

LDHC: the ultimate testis-specific gene

Lactate dehydrogenase C (LDHC) was, to the best of our knowledge, the first testis-specific isozyme discovered in male germ cells. In fact, this was accomplished shortly before "isozymes or isoenzymes" became a field of study. LDHC was detected initially in human spermatozoa and spermatogenic cells of the testes by gel electrophoresis. Immunohistochemistry was used to localize LDHC first in early-pachytene primary spermatocytes, with an apparent increase in quantity after meiosis, to its final localization in and on the principal piece of the sperm tail. After several decades of biologic, biochemical, and genetic investigations, we now know that the lactate dehydrogenase isozymes are ubiquitous in vertebrates, developmentally regulated, tissue and cell specific, and multifunctional. Here, we will review the history of LDHC and the work that demonstrates clearly that it is required for sperm to accomplish their ultimate goal, fertilization.

Gene Regulation in Spermatogenesis

Mammalian spermatogenesis is a complex hormone-dependent developmental program in which a myriad of events must take place to ensure that germ cells reach their proper stage of development at the proper time. Many of these events are controlled by cell type- and stage-specific transcription factors. The regulatory mechanisms involved provide an intriguing paradigm for the field of developmental biology and may lead to the development of new contraceptives an and innovative routs to treat male infertility. In this review, we address three aspects of the genetic regulatory mechanism that drive spermatogenesis. First, we detail what is known about how steroid hormones (both androgens and estrogens) and their cognate receptors initiate and maintain mammalian spermatogenesis. Steroids act through three mechanistic routes: (i) direct activation of genes through hormone-dependent promoter elements, (ii) secondary transcriptional responses through activation of hormone-dependent transcription factors, and (iii) rapid, transcription-independent (nonclassical) events induced by steroid hormones. Second, we provide a survey of transcription factors that function in mammalian spermatogenesis, including homeobox, zinc-finger, heat-shock, and cAMP-response family members. Our survey is not intended to cover all examples but to give a flavor for the gamut of biological roles conferred by transcription factors in the testis, particularly those defined in knockout mice. Third, we address how testis-specific transcription is achieved. In particular, we cover the evidence for and against the idea that some testis-specific genes are transcriptionally silent in somatic tissues as a result of DNA methylation.

Laboratory markers and germ cell tumors

The International Germ Cell Consensus Classification (IGCCC) of testicular germ cell tumors (TGCT) in 1997 included three serum tumor markers, serum lactate dehydrogenase catalytic concentration (S-LD), serum alpha fetoprotein concentration (S-AFP), and serum human chorionic gonadotropin concentration (S-hCG). The recommendation should be implemented for all patients with TGCT and is also useful for patients with ovarian and extragonadal germ cell tumors. A fourth serum tumor marker for TGCT, S-LD isoenzyme 1 (S-LD-1), is also relevant for TGCT. Patients with seminoma have a raised S-LD-1 more often than a raised S-AFP and S-hCG, whereas patients with nonseminoma have a raised S-AFP more often than a raised S-LD-1 and S-hCG. A new model combining IGCCC and S-LD-1 predicts survival better than previous staging systems. LD-1 is related to a characteristic chromosomal abnormality in all types of TGCT, a high copy number of chromosome 12p. In contrast, AFP and hCG are found mainly in nonseminomatous germ cell tumors and they related to the histologic differentiation of the tumors. The different biologic background for the serum tumor markers may contribute to the difference in their clinical behavior.

Regulation of ALF gene expression in somatic and male germ line tissues involves partial and site-specific patterns of methylation

ALF (TFIIAalpha/beta-like factor) is a germ cell-specific counterpart of the large (alpha/beta) subunit of general transcription factor TFIIA. Here we isolated homologous GC-rich promoters from the mouse and human ALF genes and used promoter deletion analysis to identify sequences active in COS-7 and 293 cells. Further, bisulfite sequence analysis of the mouse ALF promoter showed that all 21 CpG dinucleotides between -179 and +207 were partially methylated in five somatic tissues, brain, heart, liver, lung, and muscle, and in epididymal spermatozoa from adult mice. In contrast, DNA from prepubertal mouse testis and from purified spermatocytes were unmethylated except at C(+19)G and C(+170)G. We also found that ALF expression correlates with a strong promoter-proximal DNase I-hypersensitive site present in nuclei from testis but not from liver. Finally we show that in vitro methylation of the ALF promoter inhibits activity and that 5-aza-2'-deoxycytidine treatment reactivates the endogenous ALF gene in a panel of seven different mouse and human somatic cell lines. Overall the results show that silencing in somatic cells is methylation-dependent and reversible and that a unique CpG-specific methylation pattern at the ALF promoter precedes expression in pachytene spermatocytes. This pattern is transient as remethylation of the ALF promoter in haploid germ cell DNA has occurred by the time spermatozoa are present in the epididymis.

Methylation of CpG dinucleotides alters binding and silences testis-specific transcription directed by the mouse lactate dehydrogenase C promoter

The mouse lactate dehydrogenase c gene (mldhc) is transcribed only in cells of the germinal epithelium. Cloning and analysis of the mldhc promoter revealed that a 100-base pair fragment was able to drive testis-specific transcription in vitro and in transgenic mice. Several testis-specific genes are believed to be regulated at least in part through differential methylation of CpG dinucleotides. We investigated the possibility that transcriptional repression of the mldhc gene is mediated in somatic tissues by hypermethylation of CpG dinucleotides. The CpG dinucleotides within a fragment of the mldhc promoter containing a GC box and tandem activating transcription factor/cAMP-responsive element binding sites are hypermethylated in somatic tissues and hypomethylated in testis. Methylation of the activating transcription factor/cAMP-responsive elements altered the protein binding pattern observed in electrophoretic mobility shift assays using mouse liver but not testis nuclear extract. Furthermore, methylation of an extended mldhc promoter fragment driving lac Z silenced transcription from the promoter in a transient transfection assay. These data suggest that tissue-specific differential methylation plays a role in mldhc silencing in somatic tissues.

A possible meiotic function of the peculiar patterns of gene expression in mammalian spermatogenic cells

This review focuses on the striking differences in the patterns of transcription and translation in somatic and spermatogenic cells in mammals. In early haploid cells, mRNA translation evidently functions to restrict the synthesis of certain proteins, notably protamines, to transcriptionally inert late haploid cells. However, this does not explain why a substantial proportion of virtually all mRNA species are sequestered in translationally inactive free-messenger ribonucleoprotein particles (free-mRNPs) in meiotic cells, since most mRNAs undergo little or no increase in translational activity in transcriptionally active early haploid cells. In addition, most mRNAs in meiotic cells appear to be overexpressed because they are never fully loaded on polysomes and the levels of the corresponding protein are often much lower than the mRNA and are sometimes undetectable. A large number of genes are expressed at grossly higher levels in meiotic and/or early haploid spermatogenic cells than in somatic cells, yet they too are translated inefficiently. Many genes utilize alternative promoters in somatic and spermatogenic cells. Some of the resulting spermatogenic cell-altered transcripts (SCATs) encode proteins with novel functions, while others contain features in their 5'-UTRs, secondary structure or upstream reading frames, that are predicted to inhibit translation. This review proposes that the transcriptional machinery is modified to provide access to specific DNA sequences during meiosis, which leads to mRNA overexpression and creates a need for translational fine-tuning to prevent deleterious consequences of overproducing proteins.

DNA methylation is the primary silencing mechanism for a set of germ line- and tumor-specific genes with a CpG-rich promoter

A subset of male germ line-specific genes, the MAGE-type genes, are activated in many human tumors, where they produce tumor-specific antigens recognized by cytolytic T lymphocytes. Previous studies on gene MAGE-A1 indicated that transcription factors regulating its expression are present in all tumor cell lines whether or not they express the gene. The analysis of two CpG sites located in the promoter showed a strong correlation between expression and demethylation. It was also shown that MAGE-A1 transcription was induced in cell cultures treated with demethylating agent 5'-aza-2'-deoxycytidine. We have now analyzed all of the CpG sites within the 5' region of MAGE-A1 and show that for all of them, demethylation correlates with the transcription of the gene. We also show that the induction of MAGE-A1 with 5'-aza-2'-deoxycytidine is stable and that in all the cell clones it correlates with demethylation, indicating that demethylation is necessary and sufficient to produce expression. Conversely, transfection experiments with in vitro-methylated MAGE-A1 sequences indicated that heavy methylation suffices to stably repress the gene in cells containing the transcription factors required for expression. Most MAGE-type genes were found to have promoters with a high CpG content. Remarkably, although CpG-rich promoters are classically unmethylated in all normal tissues, those of MAGE-A1 and LAGE-1 were highly methylated in somatic tissues. In contrast, they were largely unmethylated in male germ cells. We conclude that MAGE-type genes belong to a unique subset of germ line-specific genes that use DNA methylation as a primary silencing mechanism.

Regulation of transcription of the testis-specific histone H1t gene by multiple promoter elements

This is a review of mechanisms that contribute to testis-specific transcription of the histone H1t gene. The mammalian testis-specific histone H1t gene is transcribed only in primary spermatocytes during spermatogenesis. Linker histones bind to DNA and contribute to chromatin condensation by formation of the 30 nm chromatin fiber. Furthermore, linker histones contribute to regulation of transcription of specific genes. Histone H1t, which binds more weakly to DNA than the other six known linker histones, is expressed in cells that are involved in the essential processes of crossing over and mismatch repair of DNA and in cells that undergo a dramatic alteration in gene expression. However, contributions of this linker histone to these processes are unknown. Subtle differences are found in the H1t promoter compared to the other H1 promoters. Nevertheless, several lines of evidence support the hypothesis that a sequence element designated TE that is located within the H1t promoter is essential for enhanced testis-specific transcription of this gene. Transgenic mice bearing a rat H1t transgene which contains a replacement of the TE element with stuffer DNA fail to express rat H1t mRNA. In addition, an upstream sequence appears to function as a silencer element that leads to transcriptional repression of the H1t gene in nongerminal cells. Thus, multiple promoter elements appear to contribute to regulation of transcription of the histone H1t gene.