Significance The mitotic checkpoint system has an important role to ensure accurate segregation of chromosomes in mitosis. This system regulates the activity of the ubiquitin ligase Anaphase-Promoting Complex/Cyclosome (APC/C) by the formation of a negatively acting Mitotic Checkpoint Complex (MCC). When the checkpoint is satisfied, MCC is disassembled, but the mechanisms of MCC disassembly are not well understood. We show here that the ATP-hydrolyzing enzyme Thyroid Receptor Interacting Protein 13 (TRIP13), along with the MCC-targeting protein p31 comet , promote the disassembly of the mitotic checkpoint complexes and the inactivation of the mitotic checkpoint. The results reveal an important molecular mechanism in the regulation of APC/C by the mitotic checkpoint.

The term sarcopenia describes the loss of skeletal muscle mass, strength, and function in old age. As the world population continues to grow older, more attention is given to the phenomena of sarcopenia and the search for strategies of prevention and treatment. The progression of sarcopenia is affected by age-related physiological and systemic changes in the body, including alterations in skeletal muscle tissue, hormonal changes, increased inflammatory activities, and oxidative stress. Sarcopenia progression is also affected by lifestyle factors which are far more controllable. These factors include various aspects of nutrition, physical activity, exercise, alcohol intake, and tobacco use. Raising the public awareness regarding the impact of these factors, as causes of sarcopenia and potential strategies of prevention and treatment, is of great importance. In this review we aim to describe various lifestyle factors that affect the etiology, prevention, and treatment of sarcopenia.

Sarcopenia, the age-related loss of muscle mass and strength, is a multifactorial impaired state of health. Lifestyle habits such as physical activity and nutrition have a major impact on sarcopenia progression. Several epidemiological studies have also shown an association between cigarette smoking and increased levels of sarcopenia in elderly long-time smokers. Clinical, in vivo, and in vitro studies have tried to investigate the mechanism behind exposure to cigarette smoke (CS) and the subsequent effects on skeletal muscles. The aim of this review is to present a cellular model of CS-induced skeletal muscle protein breakdown based on recent studies dealing with this issue and to propose new potential research directions that may explain the effects of exposure to CS on skeletal muscle integrity.

The AAA-ATPase thyroid hormone receptor interacting protein 13 (TRIP13), jointly with the Mad2-binding protein p31comet, promotes the inactivation of the mitotic (spindle assembly) checkpoint by disassembling the mitotic checkpoint complex (MCC). This checkpoint system ensures the accuracy of chromosome segregation by delaying anaphase until correct bipolar attachment of chromatids to the mitotic spindle is achieved. MCC inhibits the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that targets for degradation securin, an inhibitor of anaphase initiation. MCC is composed of the checkpoint proteins Mad2, BubR1, and Bub3, in association with the APC/C activator Cdc20. The assembly of MCC in active checkpoint is initiated by the conversion of Mad2 from an open (O-Mad2) to a closed (C-Mad2) conformation, which then binds tightly to Cdc20. Conversely, the disassembly of MCC that takes place when the checkpoint is turned off involves the conversion of C-Mad2 back to O-Mad2. Previously, we found that the latter process is mediated by TRIP13 together with p31comet, but the mode of their interaction remained unknown. Here, we report that the oligomeric form of TRIP13 binds both p31comet and MCC. Furthermore, p31comet and checkpoint complexes mutually promote the binding of each other to oligomeric TRIP13. We propose that p31comet bound to C-Mad2–containing checkpoint complex is the substrate for the ATPase and that the substrate-binding site of TRIP13 is composed of subsites specific for p31comet and C-Mad2–containing complex. The simultaneous occupancy of both subsites is required for high-affinity binding to TRIP13.

The age-related loss of muscle mass and strength also known as sarcopenia is significantly influenced by life style factors such as physical inactivity and impaired nutrition. Cigarette smoking is another life style habit that has been shown to be associated with sarcopenia and to affect skeletal muscle. Even today, smoking is still prevalent worldwide and is probably the most significant source of toxic chemicals exposure to humans. Cigarette smoke (CS) is a complex aerosol consisting of thousands of various constituents including reactive oxygen and nitrogen free radicals, toxic aldehydes and more. Previous epidemiological studies have identified tobacco smoking as a risk factor for sarcopenia. Clinical, in vivo and in vitro studies have revealed CS-induced skeletal muscle damage due to impaired muscle metabolism, increased inflammation and oxidative stress, over-expression of atrophy related genes and activation of various intracellular signaling pathways. This review aims to discuss and identify the components of CS that may promote catabolism of skeletal muscle.