Emergence of Novel Type C Botulism Strain in Household Outbreak, Japan.

In 2021, an outbreak of food poisoning caused by Clostridium botulinum type C occurred in Kumamoto, Japan. Analysis of the isolated strain revealed that it possessed the bont/C gene and was slightly different from the reference bont/C gene. The risk for human infection with this new toxin type may be low.

Chromosomal location of the DnaA-reactivating sequence DARS2 is important to regulate timely initiation of DNA replication in Escherichia coli.

In Escherichia coli, the initiator protein ATP-DnaA promotes initiation of chromosome replication in a timely manner. After initiation, DnaA-bound ATP is hydrolyzed to yield ADP-DnaA, which is inactive in initiation. DnaA-reactivating sequences (DARS1 and DARS2) on the chromosome have predominant roles in catalysis of nucleotide exchange, producing ATP-DnaA from ADP-DnaA, which is prerequisite for timely initiation. Both DARS sequences have a core region containing a cluster of three DnaA-binding sites. DARS2 is more effective in vivo than DARS1, and timely activation of DARS2 depends on binding of two nucleoid-associated proteins, IHF and Fis. DARS2 is located centrally between the chromosomal replication origin oriC and the terminus region terC. We constructed mutants in which DARS2 was translocated to several chromosomal loci, including sites proximal to oriC and to terC. Replication initiation was inhibited in cells in which DARS2 was translocated to terC-proximal sites when the cells were grown at 42 °C, although overall binding efficiency of IHF and Fis to the translocated DARS2 was not affected. Inhibition was largely sustained even in cells lacking MatP, a DNA-binding protein responsible for terC-specific subchromosomal structure. These results suggest that functional regulation of DARS2 is correlated with its chromosomal location under certain conditions.

Inhibition of STAT3 by Anticancer Drug Bendamustine.

Bendamustine (BENDA), which bears the bis(2-chloroethyl)amino moiety, is an alkylating agent that stops the growth of cancer cells by binding to DNA and interfering with its replication. However, the mechanism of action underlying its excellent clinical efficacy remains unclear. In this work, we report that BENDA inhibits signal transducer and activator of transcription 3 (STAT3). In an AlphaScreen-based biochemical assay using recombinant human STAT3, binding of STAT3-Src homology 2 (SH2) to the phosphotyrosine (pTyr, pY) peptide was inhibited by BENDA but not by the inactive metabolite dihydroxy bendamustine (HP2). When a single point mutation of C550A or C712A was introduced into recombinant human STAT3, its sensitivity to BENDA was substantially reduced, suggesting that these cysteine residues are important for BENDA to inhibit STAT3. Furthermore, BENDA suppressed the function of cellular STAT3 as a transcriptional activator in a human breast cancer cell line, MDA-MB-468, with constitutively activated STAT3. A competitive pull-down assay using biotinylated BENDA (Bio-BENDA) revealed that BENDA bound tightly to cellular STAT3, presumably through covalent bonds. Therefore, our results suggest that the anticancer effects of BENDA may be associated, at least in part, with its inhibitory effect on the SH2 domain of STAT3.

Direct inhibition of STAT signaling by platinum drugs contributes to their anti-cancer activity.

Platinum-based chemotherapeutics are amongst the most powerful anti-cancer drugs. Although their exact mechanism of action is not well understood, it is thought to be mediated through covalent DNA binding. We investigated the effect of platinum-based chemotherapeutics on signaling through signal transducer and activator of transcription (STAT) proteins, which are involved in many oncogenic signaling pathways. We performed in vitro experiments in various cancer cell lines, investigating the effects of platinum chemotherapeutics on STAT phosphorylation and nuclear translocation, the expression of STAT-modulating proteins and downstream signaling pathways. Direct binding of platinum to STAT proteins was assessed using an AlphaScreen assay. Nuclear STAT3 expression was determined by immunohistochemistry and correlated with disease-free survival in retrospective cohorts of head and neck squamous cell carcinoma (HNSCC) patients treated with cisplatin-based chemoradiotherapy (n= 65) or with radiotherapy alone (n = 32). At clinically relevant concentrations, platinum compounds inhibited STAT phosphorylation, resulting in loss of constitutively activated STAT proteins in multiple distinct cancer cell lines. Platinum drugs specifically inhibited phospho-tyrosine binding to SH2 domains, thereby blocking STAT activation, and subsequently downregulating pro-survival- and anti-apoptotic- target genes. Importantly, we found that active STAT3 in tumors directly correlated with response to cisplatin-based chemoradiotherapy in HNSCC patients (p = 0.006). These findings provide insight into a novel, non-DNA-targeted mechanism of action of platinum drugs, and could be leveraged into the use of STAT expression as predictive biomarker for cisplatin chemotherapy and to potentiate other therapeutic strategies such as immunotherapy.