Differential effect of ionizing radiation exposure on multipotent and differentiation‐restricted bone marrow mesenchymal stem cells

Debilitating effects of bone marrow from ionizing radiation exposure has been well established for hematopoietic stem cells; however, radiation toxicity of mesenchymal stem cells (MSCs) has been controversial. The present study addressed if ionizing radiation exposure differently affected bone marrow MSCs with various differentiation commitments. Mouse bone‐marrow‐derived MSCs, D1 cells of early passages (≤5 passages; p5) maintained the complete characteristics of multipotent MSCs, whereas, after ≥45 passages (p45) the differentiation capability of D1 cells became partially restricted. Both p5 and p45 D1 cells were subjected to single dose irradiation by radioactive isotope ¹³⁷Cs. Radiation treatment impaired cell renewal and differentiation activities of p5 D1 cells; however, p45 D1 cells were less affected. Radiation treatment upregulated both pro‐ and anti‐apoptotic genes of p5 D1 cells in a dose‐dependent manner, potentially resulting in the various apoptosis thresholds. It was found that constitutive as well as radiation‐induced phosphorylation levels of histone H2AX was significantly higher in p45 D1 cells than in p5 D1 cells. The increased repair activity of DNA double‐strand breakage may play a role for p45 D1 cells to exhibit the relative radioresistance. In conclusion, the radiation toxicity predominantly affecting multipotent MSCs may occur at unexpectedly low doses, which may, in part, contribute to the catabolic pathology of bone tissue. J. Cell. Biochem. 111: 322–332, 2010. © 2010 Wiley‐Liss, Inc.     

Regulation of IGFBP6 gene and protein is mediated by the inverse expression and function of c-jun N-terminal kinase (JNK) and NFκB in a model of oral tumor cells

The aim of this study is to identify potential gene and protein targets when nuclear factor kappa B (NFκB) and c-jun N-terminal kinase (JNK) were inversely expressed in oral tumors. To determine which genes were regulated synergistically by the inverse expression of NFκB and JNK, a pathway specific microarray analysis was performed. While either inhibition of NFκB or activation of JNK alone was unable to affect the IGFBP6 gene expression in microarray analysis, concomitant increase in JNK activation in the presence of NFκB inhibition increased the expression of this gene significantly. Synergistic increase in IGFBP6 gene expression was also confirmed by RT-PCR and Northern blot analysis of transfected cells. Accordingly, the levels of IGFBP6 protein secretion rose synergistically when JNK was over-expressed in NFκB knock down cells. In addition, increased expression of JNK in the absence of NFκB resulted in a significant induction of cell death in oral tumors when either left untreated or treated with TNF-α and TPA. Moreover, when JNK was inhibited by dominant negative JNK (APF), a significant decrease in cell death could be observed in TNF-α and TPA treated NFκB knock down oral tumors. Therefore, increased induction of IGFBP6 gene or protein expression in oral tumors could be regarded as a potential predictive marker of tumor sensitivity and could be used for prognostic purposes, since a significant correlation could be observed between increased induction of apoptotic cell death and elevated levels of IGFBP6 in these tumors.     

HPC2 variants and screen-detected prostate cancer

Two studies have reported significant associations between susceptibility to prostate cancer and two common missense variants of the HPC2/ELAC2 gene, with estimated relative risks in the range of two- to threefold. We investigated whether these polymorphisms could be informative in the prediction of the presence of prostate cancer in men undergoing prostatic biopsy for the evaluation of an elevated serum-PSA level (> or = 4.0 ng/ml). We genotyped 944 men who underwent a prostate biopsy at our institution, as well as a control population of 922 healthy, unselected women from the same population. The prevalence of the HPC2 Ala541Thr allele was similar in men with prostate cancer (6.3%), men with other prostatic conditions (6.8%), and healthy women (6.3%) (P = .83). We conclude that HPC2 genotyping is unlikely to be a useful adjunct to PSA in the prediction of the presence of biopsy-detected prostate cancer in asymptomatic men.     

Revised limit cycle oscillator model of human circadian pacemaker

In 1990, Kronauer proposed a mathematical model of the effects of light on the human circadian pacemaker. This study presents several refinements to Kronauer's original model of the pacemaker that enable it to predict more accurately the experimental results from a number of different studies of the effects of the intensity, timing, and duration of light stimuli on the human circadian pacemaker. These refinements include the following: The van der Pol oscillator from Kronauer's model has been replaced with a higher order limit cycle oscillator so that the system's amplitude recovery is slower near the singularity and faster near the limit cycle; the phase and amplitude of the circadian rhythm in sensitivity to light from Kronauer's model has been refined so that the peak sensitivity to light on the limit cycle now occurs approximately 4 h before the core body temperature minimum (CBTmin) and is three times as great as the minimum sensitivity on the limit cycle; the critical phase (at which type 1 phase response curves [PRCs] can be distinguished from type 0 PRCs) that occurs at CBT,n now corresponds to 0.8 h after the minimum of x (x(min) in this refined model rather than to the exact timing of x(min) as in Kronauer's model; a direct effect of light on circadian period was incorporated into the model such that as light intensity increases, the period decreases, which is in accordance with Aschoff's rule.     

C-terminal processing of the toxoplasma protein MIC2 is essential for invasion into host cells

Host cell invasion by apicomplexan parasites is accompanied by the rapid, polarized secretion of parasite proteins that are involved in cell attachment. The Toxoplasma gondii micronemal protein MIC2 contains several extracellular adhesive domains, a transmembrane domain, and a short cytoplasmic tail. Following apical secretion, MIC2 is transiently present on the parasite surface before being translocated backward and released by proteolytic cleavage. Mutations in the extracellular domain of MIC2, directly upstream of the transmembrane domain, prevented processing and release of the soluble protein into the supernatant. A conserved basic residue in MIC2 was essential for cleavage, and basic residues are similarly positioned in other microneme proteins. Following the induction of secretion, MIC2 processing mutants were stably expressed on the surface of the parasite. Surface MIC2-expressing mutants showed increased adhesion to host cells, yet were impaired in their capacity to invade. These data demonstrate that proteolysis is essential for releasing cell surface adhesins prior to cell entry by apicomplexan parasites.     

Effects of confinement in chaperonin assisted protein folding: rate enhancement by decreasing the roughness of the folding energy landscape

Chaperonins, such as the GroE complex of the bacteria Escherichia coli, assist the folding of proteins under non-permissive folding conditions by providing a cavity in which the newly translated or translocated protein can be encapsulated. Whether the chaperonin cage plays a passive role in protecting the protein from aggregation, or an active role in accelerating folding rates, remains a matter of debate. Here, we investigate the role of confinement in chaperonin mediated folding through molecular dynamics simulations. We designed a substrate protein with an alpha/beta sandwich fold, a common structural motif found in GroE substrate proteins and confined it to a spherical hydrophilic cage which mimicked the interior of the GroEL/ES cavity. The thermodynamics and kinetics of folding were studied over a wide range of temperature and cage radii. Confinement was seen to significantly raise the collapse temperature, T(c), as a result of the associated entropy loss of the unfolded state. The folding temperature, T(f), on the other hand, remained unaffected by encapsulation, a consequence of the folding mechanism of this protein that involves an initial collapse to a compact misfolded state prior to rearranging to the native state. Folding rates were observed to be either accelerated or retarded compared to bulk folding rates, depending on the temperature of the simulation. Rate enhancements due to confinement were observed only at temperatures above the temperature T(m), which corresponds to the temperature at which the protein folds fastest. For this protein, T(m) lies above the folding temperature, T(f), implying that encapsulation alone will not lead to a rate enhancement under conditions where the native state is stable (T相似文献