Protein degradation and modification. Introduction and overview

Proapoptotic fibronectin fragment induces the degradation of ubiquitinated p53 via proteasomes in periodontal ligament cells

BACKGROUND AND OBJECTIVE

The extracellular matrix (ECM) plays a key role in signaling necessary for tissue remodeling and cell survival. However, signals from the ECM altered by disease, e.g. inflammatory diseases such as periodontitis and arthritis, may lead to apoptosis or programmed cell death of resident cells. Previously, we found that a disease-associated fibronectin fragment triggers apoptosis of primary human periodontal ligament cells via a novel apoptotic pathway in which the tumor suppressor, p53, is transcriptionally downregulated.

MATERIAL AND METHODS

We used immunofluorescence, transfection assays, western blotting and ELISAs to show that p53 is degraded by a proteasomal pathway in response to a proapoptotic disease-associated fibronectin fragment.

RESULTS

We found that in these apoptotic conditions, p53 is further downregulated by post-translational ubiquitination and subsequent targeting to proteasomes for degradation. Pretreatment of cells with the proteasomal inhibitors MG132 and lactacystin rescued the cells from apoptosis. The p53 levels in cells transfected with ubiquitin small interfering RNA were resistant to degradation induced by the proapoptotic fibronectin fragment, showing that ubiquitination is important for the proapoptotic fibronectin fragment-induced degradation of p53.

CONCLUSION

These data show that a proapoptotic fibronectin matrix induces ubiquitination and degradation of p53 in the proteasome as part of a novel mechanism of apoptosis associated with inflammatory diseases.

The role of macroautophagy in the ageing process, anti-ageing intervention and age-associated diseases

Macroautophagy is a degradation/recycling system ubiquitous in eukariotic cells, which generates nutrients during fasting under the control of amino acids and hormones, and contributes to the turnover and rejuvenation of cellular components (long-lived proteins, cytomembranes and organelles). Tight coupling between these two functions may be the weak point in cell housekeeping. Ageing denotes a post-maturational deterioration of tissues and organs with the passage of time, due to the progressive accumulation of the misfunctioning cell components because of oxidative damage and an age-dependent decline of turnover rate and housekeeping. Caloric restriction (CR) and lower insulin levels may slow down many age-dependent processes and extend lifespan. Recent evidence is reviewed showing that autophagy is involved in ageing and in the anti-ageing action of anti-ageing calorie restriction: function of autophagy declines during adulthood and is almost negligible at older age; CR prevents the age-dependent decline of autophagic proteolysis and improves the sensitivity of liver cells to stimulation of lysosomal degradation; protection of autophagic proteolysis from the age-related decline co-varies with the duration and level of anti-ageing food restriction like the effects of CR extending lifespan; the pharmacological stimulation of macroautophagy has anti-ageing effects. Besides the involvement in ageing, macroautophagy may have an essential role in the pathogenesis of many age-associated diseases. Higher protein turnover may not fully account for the anti-ageing effects of macroautophagy, and effects of macroautophagy on housekeeping of the cell organelles, antioxidant machinery of cell membranes and transmembrane cell signaling should also be considered.

Molecular basis of skeletal muscle plasticity--from gene to form and function

Skeletal muscle shows an enormous plasticity to adapt to stimuli such as contractile activity (endurance exercise, electrical stimulation, denervation), loading conditions (resistance training, microgravity), substrate supply (nutritional interventions) or environmental factors (hypoxia). The presented data show that adaptive structural events occur in both muscle fibres (myofibrils, mitochondria) and associated structures (motoneurons and capillaries). Functional adaptations appear to involve alterations in regulatory mechanisms (neuronal, endocrine and intracellular signalling), contractile properties and metabolic capacities. With the appropriate molecular techniques it has been demonstrated over the past 10 years that rapid changes in skeletal muscle mRNA expression occur with exercise in human and rodent species. Recently, gene expression profiling analysis has demonstrated that transcriptional adaptations in skeletal muscle due to changes in loading involve a broad range of genes and that mRNA changes often run parallel for genes in the same functional categories. These changes can be matched to the structural/functional adaptations known to occur with corresponding stimuli. Several signalling pathways involving cytoplasmic protein kinases and nuclear-encoded transcription factors are recognized as potential master regulators that transduce physiological stress into transcriptional adaptations of batteries of metabolic and contractile genes. Nuclear reprogramming is recognized as an important event in muscle plasticity and may be related to the adaptations in the myosin type, protein turnover, and the cytoplasma-to-myonucleus ratio. The accessibility of muscle tissue to biopsies in conjunction with the advent of high-throughput gene expression analysis technology points to skeletal muscle plasticity as a particularly useful paradigm for studying gene regulatory phenomena in humans.