The ubiquitin-mediated degradation of mitotic cyclins is required for cells to exit from mitosis. Previous work with cell-free systems has revealed four components required for cyclin-ubiquitin ligation and proteolysis: a nonspecific ubiquitin-activating enzyme E1, a soluble fraction containing a ubiquitin carrier protein activity called E2-C, a crude particulate fraction containing a ubiquitin ligase (E3) activity that is activated during M-phase, and a constitutively active 26S proteasome that degrades ubiquitinated proteins. Here, we identify a novel approximately 1500-kDa complex, termed the cyclosome, which contains a cyclin-selective ubiquitin ligase activity, E3-C. E3-C is present but inactive during interphase; it can be activated in vitro by the addition of cdc2, enabling the transfer of ubiquitin from E2-C to cyclin. The kinetics of E3-C activation suggest the existence of one or more intermediates between cdc2 and E3-C. Cyclosome-associated E3-C acts on both cyclin A and B, and requires the presence of wild-type N-terminal destruction box motifs in each cyclin. Ubiquitinated cyclins are then rapidly recognized and degraded by the proteasome. These results identify the cyclosome-associated E3-C as the component of the cyclin destruction machinery whose activity is ultimately regulated by cdc2 and, as such, the element directly responsible for setting mitotic cyclin levels during early embryonic cell cycles.

Objective Radiation proctitis (RP) is a complication of pelvic radiotherapy which affects both the host and microbiota. Herein we assessed the radiation effect on microbiota and its relationship to tissue damage using a rectal radiation mouse model. Design We evaluated luminal and mucosa-associated dysbiosis in irradiated and control mice at two postradiation time points and correlated it with clinical and immunological parameters. Epithelial cytokine response was evaluated using bacterial-epithelial co-cultures. Subsequently, germ-free (GF) mice were colonised with postradiation microbiota and controls and exposed to radiation, or dextran sulfate-sodium (DSS). Interleukin (IL)-1β correlated with tissue damage and was induced by dysbiosis. Therefore, we tested its direct role in radiation-induced damage by IL-1 receptor antagonist administration to irradiated mice. Results A postradiation shift in microbiota was observed. A unique microbial signature correlated with histopathology.

Smoking has a broad range of physiological effects, such as being a risk factor in osteoporosis, bone fracture incidence, and increased nonunion rates. Recent studies showed that nicotine has effects at the cellular level in human osteoblast cells. To identify possible mechanisms underlying nicotine-induced changes in osteogenic metabolism, we defined changes in proliferation and osteocalcin, type I collagen, and alkaline phosphatase gene expression after treating human osteosarcoma cells (MG63), with various concentration of nicotine. Nicotine affects cell proliferation in a biphasic manner, including toxic and antiproliferative effects at high levels of nicotine and stimulatory effects at low levels. Moreover, low levels of nicotine upregulated osteocalcin, type I collagen, and alkaline phosphatase gene expression. The increased cell proliferation and gene upregulation induced by nicotine were inhibited by addition of the nicotinic receptor antagonist D: -tubocurarine. High nicotine concentrations downregulated the investigated genes. Our results demonstrate, for the first time, that the addition of nicotine concentrations analogous to those acquired by a light to moderate smoker yields increased osteoblast proliferation and bone metabolism, whereas the addition of nicotine concentrations analogous to heavy smokers leads to the opposite effect. The inhibition of these effects by D: -tubocurarine suggests that nicotine acts via the nicotinic acetylcholine receptor (nAChR).

SUMMARY BackgroundAdalimumab is an effective treatment for Crohn's disease (CD). Antiadalimumab antibodies (AAA) and low trough serum drug concentrations have been implicated as pre-disposing factors for treatment failure.