The Multifaceted Roles of the Tumor Susceptibility Gene 101 (TSG101) in Normal Development and Disease.

The multidomain protein encoded by the () is ubiquitously expressed and is suggested to function in diverse intracellular processes. In this review, we provide a succinct overview of the main structural features of the protein and their suggested roles in molecular and cellular functions. We then summarize, in more detail, key findings from studies using genetically engineered animal models that demonstrate essential functions of TSG101 in cell proliferation and survival, normal tissue homeostasis, and tumorigenesis.

Distinct roles for DNA-PK, ATM and ATR in RPA phosphorylation and checkpoint activation in response to replication stress.

DNA damage encountered by DNA replication forks poses risks of genome destabilization, a precursor to carcinogenesis. Damage checkpoint systems cause cell cycle arrest, promote repair and induce programed cell death when damage is severe. Checkpoints are critical parts of the DNA damage response network that act to suppress cancer.

A knockout of the Tsg101 gene leads to decreased expression of ErbB receptor tyrosine kinases and induction of autophagy prior to cell death.

The Tumor Susceptibility Gene 101 (Tsg101) encodes a multi-domain protein that mediates a variety of molecular and biological processes including the trafficking and lysosomal degradation of cell surface receptors. Conventional and conditional knockout models have demonstrated an essential requirement of this gene for cell cycle progression and cell viability, but the consequences of a complete ablation of Tsg101 on intracellular processes have not been examined to date. In this study, we employed mouse embryonic fibroblasts that carry two Tsg101 conditional knockout alleles to investigate the expression of ErbB receptor tyrosine kinases as well as stress-induced intracellular processes that are known to be associated with a defect in growth and cell survival.

Helicobacter hepaticus cytolethal distending toxin causes cell death in intestinal epithelial cells via mitochondrial apoptotic pathway.

Background: Helicobacter hepaticus, the prototype for enterohepatic Helicobacter species, colonizes the lower intestinal and hepatobiliary tracts of mice and causes typhlocolitis, hepatitis, and hepatocellular carcinoma in susceptible mouse strains. Cytolethal distending toxin (CDT) is the only known virulence factor found in H. hepaticus.

Hyperphosphorylation of replication protein A in cisplatin-resistant and -sensitive head and neck squamous cell carcinoma cell lines.

Background: Resistance to chemotherapy is a major limitation in the treatment of head and neck squamous cell carcinomas (HNSCCs), accounting for high mortality rates in patients. Here, we investigated the role of replication protein A (RPA) in cisplatin and etoposide resistance.

Methods: We used 6 parental HNSCC cell lines.

NBS1 mediates ATR-dependent RPA hyperphosphorylation following replication-fork stall and collapse.

Post-translational phosphorylation of proteins provides a mechanism for cells to switch on or off many diverse processes, including responses to replication stress. Replication-stress-induced phosphorylation enables the rapid activation of numerous proteins involved in DNA replication, DNA repair and cell cycle checkpoints, including replication protein A (RPA). Here, we report that hydroxyurea (HU)-induced RPA phosphorylation requires both NBS1 (NBN) and NBS1 phosphorylation.

Riboflavin deficiency causes protein and DNA damage in HepG2 cells, triggering arrest in G1 phase of the cell cycle.

Eukaryotes convert riboflavin to flavin adenine dinucleotide, which serves as a coenzyme for glutathione reductase and other enzymes. Glutathione reductase mediates the regeneration of reduced glutathione, which plays an important role in scavenging free radicals and reactive oxygen species. Here we tested the hypothesis that riboflavin deficiency decreases glutathione reductase activity in HepG2 liver cells, causing oxidative damage to proteins and DNA, and cell cycle arrest.

HepG2 cells develop signs of riboflavin deficiency within 4 days of culture in riboflavin-deficient medium.

Flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) are essential coenzymes in redox reactions. For example, FAD is a coenzyme for both glutathione reductase and enzymes that mediate the oxidative folding of secretory proteins. Here we investigated short-term effects of moderately riboflavin-deficient culture medium on flavin-related responses in HepG2 hepatocarcinoma cells.

Riboflavin deficiency impairs oxidative folding and secretion of apolipoprotein B-100 in HepG2 cells, triggering stress response systems.

Secretory proteins such as apolipoprotein B-100 (apoB) undergo oxidative folding (formation of disulfide bonds) in the endoplasmic reticulum (ER) before secretion. Oxidative folding depends on flavoproteins in eukaryotes. Here, human liver (HepG2) cells were used to model effects of riboflavin concentrations in culture media on folding and secretion of apoB.

Biotin supply affects expression of biotin transporters, biotinylation of carboxylases and metabolism of interleukin-2 in Jurkat cells.

Biotin supply may affect transcription of genes and biotinylation of proteins in cells. In this study, Jurkat cells were used to model effects of biotin supply on biotin homeostasis and interleukin-2 metabolism in immune cells. Cells were cultured in media containing deficient (25 pmol/L), physiologic (250 pmol/L), or pharmacologic concentrations (10,000 pmol/L) of biotin for 4 wk.