Differential susceptibility to hydrogen sulfide-induced apoptosis between PHLDA1-overexpressing oral cancer cell lines and oral keratinocytes: Role of PHLDA1 as an apoptosis suppressor

Hydrogen sulfide (H₂S) is a novel gasotransmitter that plays multiple biological roles in various body systems. In addition to its endogenous production, H₂S is produced by bacteria colonizing digestive organs, including the oral cavity. H₂S was previously shown to enhance pro-apoptotic effects in cancer cell lines, although the mechanisms involved remain unclear. To properly assess the anti-cancer effects of H₂S, however, investigations of apoptotic effects in normal cells are also necessary. The aims of this study were (1) to compare the susceptibility to H₂S-induced apoptosis between the oral cancer cell line Ca9-22 and oral keratinocytes that were derived from healthy gingiva, and (2) to identify candidate genes involved in the induction of apoptosis by H₂S. The susceptibility to H₂S-induced apoptosis in Ca9-22 cells was significantly higher than that in keratinocytes. H₂S exposure in Ca9-22 cells, but not keratinocytes, enhanced the expression of pleckstrin homology-like domain, family A, member 1 (PHLDA1), which was identified through a differential display method. In addition, PHLDA1 expression increased during actinomycin D-induced apoptosis in Ca9-22 cells. Knockdown of PHLDA1 expression by small interfering RNA in Ca9-22 cells led to expression of active caspase 3, thus indicating apoptosis induction. The tongue cancer cell line SCC-25, which expresses PHLDA1 at a high level, showed similar effects. Our data indicate that H₂S is an anti-cancer compound that may contribute to the low incidence of oral cancer. Furthermore, we demonstrated the role of PHLDA1 as an apoptosis suppressor.     

Formation of Cyclohexylamine and Cyclohexanone from Cyclamate by Microorganisms Isolated from the Feces of Guinea Pig

The assimilation of sodium cyclamate (CHS-Na) by microorganisms was studied. Fifteen strains of cyclamate-assimilating bacteria were isolated from the feces of guinea pig excreting cyclohexylamine (CHA) in urine. The majority of the strain isolated seems to belong to the genera Pseudomonas and Corynebacterium. All strains were able to assimilate CHS-Na as a sole source of carbon and nitrogen, and accumulated clearly CHA in the culture medium. It was confirmed with the cell-free extract that the strains possessed the enzyme system which formed cyclohexanone (CHnone) from CHS-Na via CHA. It seems that the desulfation of CHS-Na to CHA is catalyzed by hydrolase, and that the deamination of CHA to CHnone is catalyzed by amine oxidase depending on oxygen.     

Oxygen-18 studies on the oxidative deamination mechanism of alicyclic primary amines in rabbit liver microsomes

The mechanism of microsomal oxidative deamination of alicyclic primary amines: cyclopentylamine, cyclohexylamine, cycloheptylamine, 1- and 2-aminoindan, 1- and 2-aminotetralin, was studied under an atmosphere of ¹⁸O₂ or in a medium containing H₂¹⁸O. The oxygen-18 contents of the products determined by gas-liquid chromatography/mass spectrometry revealed that almost all (75–100 atom%) of the oxygen of oximes was derived from molecular oxygen, whereas a part (4–25 atom% ) of the oxygen of ketones. The studies on the hydrolysis of oximes and the oxygen exchange reaction of ketones proved that the latter proceeded at a considerable rate ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 9.5–336}\text{min}$) and the former made a minor contribution, to explain why the major portion (75–96 atom%) of the oxygen in ketones was derived from water. The results support the mechanism that microsomal deamination proceeds mainly through a carbinolamine intermediate, which is initially hydroxylated at the α carbon to the amino group, partially equilibrating with the imine, and then rearranges to form a ketone and ammonia.     

Mutagenicity of Isothiocyanates,Isocyanates and Thioureas on Salmonella typhimurium

During the screening program for atrial natriuretic peptide (ANP) receptor ligands of microbial origin, we isolated a novel nonpeptide ANP antagonist, HS-142-1, from a culture broth of Aureo-basidium pullulans var. melanigenum. Structural analysis showed that HS-142-1 was composed of 20–30 kinds of β-1,6-glucan esterified by caproyl groups; each component had an almost equal potency. HS-142-1 inhibited [¹²⁵I]-rANP binding to its receptor in rabbit kidney cortex membranes with an IC₅₀ of 0.3μg/ml and antagonized ANP-induced cGMP production by bovine lung membranes in a dose-dependent fashion. The discovery of this nonpeptide ANP antagonist, HS-142-1, will provide a useful tool to study the physiological significance of natriuretic peptide system.     

Morphology and Chemistry of the Bacterial Cell Wall

The location of the mucopeptide in the cell wall of Bacteroides convexus was determined by electron microscope after enzymatic and chemical treatment (papain, pepsin, lysozyme and phenol). In the five layered cell wall the innermost electron dense layer (or a part of it) proved to be the mucopeptide. The molar ratio of amino sugar and amino acid components of purified mucopeptide was about 1:1:1:1:1:1 for glucosamine, muramic acid, L-alanine, D-glutamic acid, DL(meso)-diaminopimelic acid and D-alanine.