Toxin-antitoxin (TA) systems are composed of a toxin that inhibits an essential cellular process (e.g. DNA replication, transcription, membrane integrity) and its cognate antitoxin that neutralizes the effect of the toxin. Staphylococcus aureus harbors two types of chromosomally encoded TA systems, namely mazEFsa encoding a UACAU-specific mRNA interferase and two paralogous genes of yefM-yoeBsa encoding a ribosome-dependent endoribonuclease system. However, little is known about the physiological role of MazEFsa and YefM-YoeBsa in S. aureus. Upon characterizing the phenotypes of single, double and triple gene deletion mutants, we found that mazFsa deletion led to increased biofilm formation. Subsequently, transcriptional analysis revealed that expression of intercellular adhesin (ica) gene, icaADBC, increased in a mazFsa deletion mutant. mazFsa/icaADBC double gene deletion and genetic complementation approaches provided convincing evidence that increased biofilm formation was caused by an increase in polysaccharide intercellular adhesin synthesized by icaADBC-encoded proteins. Furthermore, through the use of alanine substitutions at the conserved active residues of MazFsa, our results suggested that ica-mediated biofilm formation depended on the mRNA interferase activity of MazFsa. These findings give new insights not only into the physiological role of MazEFsa in S. aureus, but also into the regulatory mechanism of ica-dependent biofilm formation.

Clathrin regulates mitotic progression, in addition to membrane trafficking. However, the detailed regulatory mechanisms of clathrin during mitosis remain elusive. Here, we demonstrate novel regulation of clathrin during mitotic phase of the cell cycle. Clathrin heavy chain (CHC) was phosphorylated at T606 by its association partner cyclin G-associated kinase (GAK). This phosphorylation was required for proper cell proliferation and tumor growth of cells implanted into nude mice. Immunofluorescence analysis showed that the localization of CHC-pT606 signals changed during mitosis. CHC-pT606 signals localized in the nucleus and at the centrosome during interphase, whereas CHC signals were mostly cytoplasmic. Co-immunoprecipitation suggested that CHC formed a complex with GAK and polo-like kinase 1 (PLK1). Depletion of GAK using siRNA induced metaphase arrest and aberrant localization of CHC-pT606, which abolished Kiz-pT379 (as a phosphorylation target of PLK1) signals on chromatin at metaphase. Taken together, we propose that the GAK_CHC-pT606_PLK1_Kiz-pT379 axis plays a role in proliferation of cancer cells.

Oral health care to increase optimal occlusal contacts and rehabilitation of trismus may be promising factors to improve the functional performance of oral cancer survivors.

We previously reported that an ELAS1 peptide containing 29 amino acids induces apoptotic death in U2OS human osteosarcoma cells following DNA double-strand break insults. Here, we show that ELAS1 also caused apoptosis in prostate adenocarcinoma DU145 cells and tongue squamous-cell carcinoma SAS cells. ELAS1 appears to be safe because it induced apoptosis only in cancer cells, not in normal KD cells. Because the effect of ELAS1 is dependent on increased stability of p53 and enhanced phosphorylation of p53-S46, we exogenously expressed wild-type p53 protein to fully promote ELAS1-mediated induction of apoptosis in SAS cells. Interestingly, simultaneous expression of Myc-ELAS1 and FLAG-p53 mediated by an internal ribosome entry site efficiently induced apoptosis in SAS cells. Moreover, we prepared a recombinant adenovirus that simultaneously expressed Myc-ELAS1 and FLAG-p53. This adenovirus also killed SAS cells, as determined by a cell viability assay, in the presence of camptothecin, an inducer of DNA double-strand breaks. Moreover, nude mice harboring Myc-ELAS1-expressing SAS cells lived longer than mice harboring Myc-vector-expressing SAS cells, suggesting the usefulness of ELAS1 in vivo. Notably, Cy5-tagged ELAS1-t, which contained only ten amino acids, also efficiently induced apoptosis in both DU145 and SAS cells, suggesting the usefulness of ELAS1-t as a peptide. Taken together, our results suggest that ELAS1 is therapeutically useful as a peptide drug.