Polyamines stimulate the CHSY1 synthesis through the unfolding of the RNA G-quadruplex at the 5'-untraslated region

Intracellular polyamine depletion induces N-linked galactosylation of the monoclonal antibody produced by CHO DP-12 cells

The heterogeneity of the N-linked glycan profile of therapeutic monoclonal antibodies (mAbs) derived from animal cells affects therapeutic efficacy and, therefore, needs to be appropriately controlled during the manufacturing process. In this study, we examined the effects of polyamines on the N-linked glycan profiles of mAbs produced by CHO DP-12 cells. Normal cell growth of CHO DP-12 cells and their growth arrest by α-difluoromethylornithine (DFMO), an inhibitor of the polyamine biosynthetic pathway, was observed when 0.5% fetal bovine serum was added to serum-free medium, despite the presence of cadaverine and aminopropylcadaverine, instead of putrescine and spermidine in cells. Polyamine depletion by DFMO increased IgG galactosylation, accompanied by β1,4-galactosyl transferase 1 (B4GAT1) mRNA elevation. Additionally, IgG production in polyamine-depleted cells was reduced by 30% compared to that in control cells. Therefore, we examined whether polyamine depletion induces an ER stress response. The results indicated increased expression levels of chaperones for glycoprotein folding in polyamine-depleted cells, suggesting that polyamine depletion causes ER stress related to glycoprotein folding. The effect of tunicamycin, an ER stress inducer that inhibits N-glycosylation, on the expression of B4GALT1 mRNA was examined. Tunicamycin treatment increased B4GALT1 mRNA expression. These results suggest that ER stress caused by polyamine depletion induces B4GALT1 mRNA expression, resulting in increased IgG galactosylation in CHO cells. Thus, introducing polyamines, particularly SPD, to serum-free CHO culture medium for CHO cells may contribute to consistent manufacturing and quality control of antibody production.

Functional roles of polyamines and their metabolite acrolein in eukaryotic cells

Among low molecular weight substances, polyamines (spermidine, spermine and their precursor putrescine) are present in eukaryotic cells at the mM level together with ATP and glutathione. It is expected therefore that polyamines play important roles in cell proliferation and viability. Polyamines mainly exist as a polyamine-RNA complex and regulate protein synthesis. It was found that polyamines enhance translation from inefficient mRNAs. The detailed mechanisms of polyamine stimulation of specific kinds of protein syntheses and the physiological functions of these proteins are described in this review. Spermine is metabolized into acrolein (CH2 = CH-CHO) and hydrogen peroxide (H2O2) by spermine oxidase. Although it is thought that cell damage is mainly caused by reactive oxygen species (O2-, H2O2, and •OH), it was found that acrolein is much more toxic than H2O2. Accordingly, the level of acrolein produced becomes a useful biomarker for several tissue-damage diseases like brain stroke. Thus, the mechanisms of cell toxicity caused by acrolein are described in this review.

RNA G-quadruplexes (rG4s): genomics and biological functions

G-quadruplexes (G4s) are non-classical DNA or RNA secondary structures that have been first observed decades ago. Over the years, these four-stranded structural motifs have been demonstrated to have significant regulatory roles in diverse biological processes, but challenges remain in detecting them globally and reliably. Compared to DNA G4s (dG4s), the study of RNA G4s (rG4s) has received less attention until recently. In this review, we will summarize the innovative high-throughput methods recently developed to detect rG4s on a transcriptome-wide scale, highlight the many novel and important functions of rG4 being discovered in vivo across the tree of life, and discuss the key biological questions to be addressed in the near future.

Translational Regulation of Clock Genes BMAL1 and REV-ERBα by Polyamines

Polyamines stimulate the synthesis of specific proteins at the level of translation, and the genes encoding these proteins are termed as the "polyamine modulon". The circadian clock generates daily rhythms in mammalian physiology and behavior. We investigated the role of polyamines in the circadian rhythm using control and polyamine-reduced NIH3T3 cells. The intracellular polyamines exhibited a rhythm with a period of about 24 h. In the polyamine-reduced NIH3T3 cells, the circadian period of circadian clock genes was lengthened and the synthesis of BMAL1 and REV-ERBα was significantly reduced at the translation level. Thus, the mechanism of polyamine stimulation of these protein syntheses was analyzed using NIH3T3 cells transiently transfected with genes encoding enhanced green fluorescent protein (EGFP) fusion mRNA with normal or mutated 5'-untranslated region (5'-UTR) of Bmal1 or Rev-erbα mRNA. It was found that polyamines stimulated BMAL1 and REV-ERBα synthesis through the enhancement of ribosomal shunting during the ribosome shunting within the 5'-UTR of mRNAs. Accordingly, the genes encoding Bmal1 and Rev-erbα were identified as the members of "polyamine modulon", and these two proteins are significantly involved in the circadian rhythm control.

Ischemic stroke disrupts the endothelial glycocalyx through activation of proHPSE via acrolein exposure

Infiltration of peripheral immune cells after blood-brain barrier dysfunction causes severe inflammation after a stroke. Although the endothelial glycocalyx, a network of membrane-bound glycoproteins and proteoglycans that covers the lumen of endothelial cells, functions as a barrier to circulating cells, the relationship between stroke severity and glycocalyx dysfunction remains unclear. In this study, glycosaminoglycans, a component of the endothelial glycocalyx, were studied in the context of ischemic stroke using a photochemically induced thrombosis mouse model. Decreased levels of heparan sulfate and chondroitin sulfate and increased activity of hyaluronidase 1 and heparanase (HPSE) were observed in ischemic brain tissues. HPSE expression in cerebral vessels increased after stroke onset and infarct volume greatly decreased after co-administration of N-acetylcysteine + glycosaminoglycan oligosaccharides as compared with N-acetylcysteine administration alone. These results suggest that the endothelial glycocalyx was injured after the onset of stroke. Interestingly, scission activity of proHPSE produced by immortalized endothelial cells and HEK293 cells transfected with hHPSE1 cDNA were activated by acrolein (ACR) exposure. We identified the ACR-modified amino acid residues of proHPSE using nano LC-MS/MS, suggesting that ACR modification of Lys139 (6-kDa linker), Lys107, and Lys161, located in the immediate vicinity of the 6-kDa linker, at least in part is attributed to the activation of proHPSE. Because proHPSE, but not HPSE, localizes outside cells by binding with heparan sulfate proteoglycans, ACR-modified proHPSE represents a promising target to protect the endothelial glycocalyx.

Polyamines regulate gene expression by stimulating translation of histone acetyltransferase mRNAs

Polyamines regulate gene expression in Escherichia coli by translationally stimulating mRNAs encoding global transcription factors. In this study, we focused on histone acetylation, one of the mechanisms of epigenetic regulation of gene expression, to attempt to clarify the role of polyamines in the regulation of gene expression in eukaryotes. We found that activities of histone acetyltransferases in both the nucleus and cytoplasm decreased significantly in polyamine-reduced mouse mammary carcinoma FM3A cells. Although protein levels of histones H3 and H4 did not change in control and polyamine-reduced cells, acetylation of histones H3 and H4 was greatly decreased in the polyamine-reduced cells. Next, we used control and polyamine-reduced cells to identify histone acetyltransferases whose synthesis is stimulated by polyamines. We found that polyamines stimulate the translation of histone acetyltransferases GCN5 and HAT1. Accordingly, GCN5- and HAT1-catalyzed acetylation of specific lysine residues on histones H3 and H4 was stimulated by polyamines. Consistent with these findings, transcription of genes required for cell proliferation was enhanced by polyamines. These results indicate that polyamines regulate gene expression by enhancing the expression of the histone acetyltransferases GCN5 and HAT1 at the level of translation. Mechanistically, polyamines enhanced the interaction of microRNA-7648-5p (miR-7648-5p) with the 5'-UTR of GCN5 mRNA, resulting in stimulation of translation due to the destabilization of the double-stranded RNA (dsRNA) between the 5'-UTR and the ORF of GCN5 mRNA. Because HAT1 mRNA has a short 5'-UTR, polyamines may enhance initiation complex formation directly on this mRNA.

KLF4 is required for suppression of histamine synthesis by polyamines during bone marrow-derived mast cell differentiation

Mast cells have secretory granules containing chemical mediators such as histamine and play important roles in the immune system. Polyamines are essential factors for cellular processes such as gene expression and translation. It has been reported that secretory granules contain both histamine and polyamines, which have similar chemical structures and are produced from the metabolism of cationic amino acids. We investigated the effect of polyamine depletion on mast cells using bone marrow-derived mast cells (BMMCs). Polyamine depletion was induced using α-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase. DFMO treatment resulted in a significant reduction of cell number and abnormal secretory granules in BMMCs. Moreover, the cells showed a 2.3-fold increase in intracellular histamine and up-regulation of histidine decarboxylase (HDC) at the transcriptional level during BMMC differentiation. Levels of the transcription factor kruppel-like factor 4 (KLF4) greatly decreased upon DFMO treatment; however, Klf4 mRNA was expressed at levels similar to controls. We determined the translational regulation of KLF4 using reporter genes encoding Klf4-luc2 fusion mRNA, for transfecting NIH3T3 cells, and performed in vitro translation. We found that the efficiency of KLF4 synthesis in response to DFMO treatment was enhanced by the existence of a GC-rich 5'-untranslated region (5'-UTR) on Klf4 mRNA, regardless of the recognition of the initiation codon. Taken together, these results indicate that the enhancement of histamine synthesis by DFMO depends on the up-regulation of Hdc expression, achieved by removal of transcriptional suppression of KLF4, during differentiation.

Chondroitin sulfate E blocks enzymatic action of heparanase and heparanase-induced cellular responses

We examined whether chondroitin sulfates (CSs) exert inhibitory effects on heparanase (Hpse), the sole endoglycosidase that cleaves heparan sulfate (HS) and heparin, which also stimulates chemokine production. Hpse-mediated degradation of HS was suppressed in the presence of glycosaminoglycans derived from a squid cartilage and mouse bone marrow-derived mast cells, including the E unit of CS. Pretreatment of the chondroitin sulfate E (CS-E) with chondroitinase ABC abolished the inhibitory effect. Recombinant proteins that mimic pro-form and mature-form Hpse bound to the immobilized CS-E. Cellular responses as a result of Hpse-mediated binding, namely, uptake of Hpse by mast cells and Hpse-induced release of chemokine CCL2 from colon carcinoma cells, were also blocked by the CS-E. CS-E may regulate endogenous Hpse-mediated cellular functions by inhibiting enzymatic activity and binding to the cell surface.