m6 RNA methylation: an emerging common target in the immune response to cancer and severe acute respiratory syndrome-coronavirus-2 infection

m6A RNA methylation, a predominant type of RNA modification, is involved in regulating mRNA splicing, stability, and translation as well as the interaction between nucleoproteins and noncoding RNAs. Recent studies have revealed that m6A RNA methylation plays a critical role in the self-to-non-self-recognition of immune cells against endogenous mutations in cancer and exogenous organism-related infections. As an epigenetic mechanism, m6A RNA modification induces immune cell signal transduction, which is altered in the tumor microenvironment, as detected in liquid biopsy. Furthermore, m6A RNA methylation-related inflammation is involved in the cellular response to viral infections, including the emerging severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection. Given the importance of the immune response in maintaining homeostasis in higher eukaryotes, m6A RNA methylation could be useful not only for the early detection of cancer but also for SARS-CoV-2 screening during a global pandemic.

Pancreatic Cancer Research beyond DNA Mutations

Pancreatic ductal adenocarcinoma (PDAC) is caused by genetic mutations in four genes: KRAS proto-oncogene and GTPase (KRAS), tumor protein P53 (TP53), cyclin-dependent kinase inhibitor 2A (CDKN2A), and mothers against decapentaplegic homolog 4 (SMAD4), also called the big 4. The changes in tumors are very complex, making their characterization in the early stages challenging. Therefore, the development of innovative therapeutic approaches is desirable. The key to overcoming PDAC is diagnosing it in the early stages. Therefore, recent studies have investigated the multifaced characteristics of PDAC, which includes cancer cell metabolism, mesenchymal cells including cancer-associated fibroblasts and immune cells, and metagenomics, which extend to characterize various biomolecules including RNAs and volatile organic compounds. Various alterations in the KRAS-dependent as well as KRAS-independent pathways are involved in the refractoriness of PDAC. The optimal combination of these new technologies is expected to help treat intractable pancreatic cancer.

COVID-19 Drug Discovery Using Intensive Approaches

Since the infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was reported in China during December 2019, the coronavirus disease 2019 (COVID-19) has spread on a global scale, causing the World Health Organization (WHO) to issue a warning. While novel vaccines and drugs that target SARS-CoV-2 are under development, this review provides information on therapeutics which are under clinical trials or are proposed to antagonize SARS-CoV-2. Based on the information gained from the responses to other RNA coronaviruses, including the strains that cause severe acute respiratory syndrome (SARS)-coronaviruses and Middle East respiratory syndrome (MERS), drug repurposing might be a viable strategy. Since several antiviral therapies can inhibit viral replication cycles or relieve symptoms, mechanisms unique to RNA viruses will be important for the clinical development of antivirals against SARS-CoV-2. Given that several currently marketed drugs may be efficient therapeutic agents for severe COVID-19 cases, they may be beneficial for future viral pandemics and other infections caused by RNA viruses when standard treatments are unavailable.

Highly efficient random mutagenesis in transcription-reverse-transcription cycles by a hydrogen bond ambivalent nucleoside 5'-triphosphate analogue: potential candidates for a selective anti-retroviral therapy

The nucleoside P can base pair with both A and G. We evaluated the mutation frequency induced by the 5'-triphospbate of the ribonucleoside P (PTP) in an in vitro retroviral replication model. After 4 cycles of replication in the presence of PTP, the mutation frequency was raised to 3.8 x 10(-2) per nucleotide and C-to-U and U-to-C mutations were dominantly observed. These results suggest that ambivalent NTP analogues, like PTP, could induce mutations beyond the error threshold of retroviruses.

The possible role of acetyltransferase in the induction of cytogenetic effects by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in cultured Chinese hamster cells

When metabolically activated, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic amine isolated from cooked food, is clastogenic in cultured Chinese hamster and human cells. Secondary metabolites of PhIP are formed via acetyltransferase (AT) and sulfotransferase (ST) activity; however, which is responsible for its clastogenic effect is unknown. We addressed this question. We used a parental Chinese hamster lung cell line and three sublines transfected with different AT genes to test the clastogenic (i.e., micronucleus-inducing) effects of metabolically activated PhIP and 7,12-dimethylbenz[a]anthracene (DMBA) in the presence and absence of pentachlorophenol (PCP), a ST inhibitor. PhIP was significantly more clastogenic in the three AT-enriched sublines than in the parental line (p < 0.001). DMBA (a ST-activated mutagen), on the other hand, equally induced MNs in all the cell lines. When PCP was added to the test system, the MN-induction ability of DMBA, but not of PhIP, decreased significantly (p < 0.001). These findings strongly suggest that PhIP clastogenicity is due to AT activity and not to ST activity.

Cytogenetic effects of a food mutagen, 2-amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine (PhIP), and its metabolite, 2-hydroxyamino-1-methy-6-phenylimidazo[4,5-beta]pyridine (N-OH-PhIP), on human and Chinese hamster cells in vitro

2-Amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine (PhIP) induced structural chromosomal aberrations (CAs) and sister-chromatid exchanges (SCEs) in human lymphocytes and human diploid fibroblasts (TIG-7) at concentrations above 12.5 microgram /ml in the presence of rat S9 mix. PhIP also elevated the frequencies of SCEs in human lymphocytes in the presence of rat S9 at concentrations above 2.0 microgram/ml with dose-dependency. A proximate form of metabolites of PhIP, 2-hydroxy-amino-1-methyl-6-phenylimidazo[4,5-beta]pyridine (N-OH-PhIP), caused CAs in human and Chinese hamster fibroblast cells in the absence of S9 mix at concentrations above 0.75 microgram/ml and 1.25 microgram/ml, respectively, which were 10 times lower than the effective concentration of PhIP. No marked differences were observed in the cytogenetic sensitivity to N-OH-PhIP between human and Chinese hamster cells, except between lymphocytes obtained from different donors.

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ), a carcinogenic pyrolysate, induces chromosomal aberrations in Chinese hamster lung fibroblasts in vitro

The ability of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) to induce chromosomal aberrations (CAs) in Chinese hamster lung fibroblast (CHL/IU) cells in vitro was examined. On incubation with rat S9 (2.5-10%, v/v) for 3 h, followed by a recovery culture period of 21 h, IQ caused significant induction of CAs at a concentration 20 micrograms/ml, but had less effect at 40 micrograms/ml. With longer recovery culture times such as 27-33 h, however, IQ was much more effective at 40 micrograms/ml. No significant induction was observed with 1 or 6 h treatments followed by 23 or 18 h recovery cultures, respectively. On incubation without S9, only weak CA induction by IQ was observed. These results show that IQ is a clastogen and that its clastogenic effect varied with the experimental conditions, such as the time of exposure and the time of recovery culture. The cell cycle perturbation effect is suggested to be one of the critical factors for the detection of the clastogenic potential of IQ.

Suppressive effect of transforming growth factor-beta on the phosphorylation of endogenous substrates by conventional and novel protein kinase C in primary cultured mouse epidermal cells

The effect of transforming growth factor-beta (TGF-beta) on the endogenous protein phosphorylation caused by phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinase C (PKC), was examined in primary cultured mouse epidermal cells. PMA markedly stimulates phosphorylation of endogenous proteins, i.e. KP-1 and KP-2, through Ca(2+)-dependent conventional PKC (cPKC), and KP-10 through Ca(2+)-independent novel PKC (nPKC) in intact epidermal cells. TGF-beta strongly suppressed the PMA-stimulated phosphorylation of these three proteins. Rate of dephosphorylation of these phosphorylated proteins was not affected by TGF-beta. Treatment of epidermal cells with TGF-beta decreased cPKC activity both in cytosolic and particulate fractions, but not nPKC activity. These results indicate that TGF-beta suppresses cPKC- and nPKC-mediated endogenous protein phosphorylation in intact epidermal cells, but the mechanisms of suppression are different.

Characterization of endogenous substrates for novel-type protein kinase C as well as conventional-type protein kinase C in primary cultured mouse epidermal cells

In primary cultured mouse epidermal cells, phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC), induced changes in the phosphorylation levels of 10 proteins, termed KP-1 to -10, in two-dimensional PAGE. Seven of these proteins were phosphorylated and three were dephosphorylated. Similar changes were induced by other PKC activators, but not by inactive phorbol ester. Among these substrate proteins, phosphorylation of three proteins, i.e. KP-1 (pI 4.7/23,000 M(r)), KP-2 (pI 4.7/20,700 M(r)) and KP-10 (pI 4.7/25,500 M(r)) was markedly enhanced by PMA and inhibited by a potent PKC inhibitor staurosporine. In vitro phosphorylation studies and phosphoamino acid analysis, using these proteins as substrate and PKC preparations obtained from epidermal cell lysate, revealed that KP-1 and -2 were directly phosphorylated by Ca(2+)-, phospholipid-dependent protein kinase (conventional-type PKC; cPKC), but not by Ca(2+)-independent, phospholipid-dependent protein kinase (novel-type PKC; nPKC). On the other hand, KP-10 was mainly phosphorylated by nPKC in intact epidermal cells. These results indicate that cPKC and nPKC in epidermal cells have different substrate specificity for endogenous proteins and may induce different signal transduction.

Involvement of prostaglandin E2 in ornithine decarboxylase induction by a tumor-promoting agent, 7-bromomethylbenz[a]anthracene, in mouse epidermis

A single topical application of 7-bromomethyl-benz[a]anthracene (BrMBA; 200 nmol) to mouse skin induced epidermal ornithine decarboxylase (ODC) activity. A topical application of indomethacin (1.2 mumol), a cyclooxygenase inhibitor, 10 min before BrMBA application markedly inhibited BrMBA-caused ODC induction. Concurrent application of prostaglandin E2 (PGE2; 0.1-1.5 mumol) reversed the inhibitory effect of indomethacin. Without indomethacin, PGE2 suppressed BrMBA-caused ODC induction. The results indicate that PGE2 has dual actions on the BrMBA-caused ODC induction, i.e. PGE2 plays an essential role in ODC induction caused by BrMBA, whereas exogenous PGE2 rather suppressed BrMBA-caused ODC induction.