The epidermal growth factor (EGF) receptor (EGFR) has been found to be overexpressed in several types of cancer cells, and the regulation of its oncogenic potential has been widely studied. The paradigm for EGFR down-regulation involves the trafficking of activated receptor molecules from the plasma membrane, through clathrin-coated pits, and into the cell for lysosomal degradation. We have previously shown that oxidative stress generated by H 2 O 2 results in aberrant phosphorylation of the EGFR. This leads to the loss of c-Cbl-mediated ubiquitination of the EGFR and, consequently, prevents its degradation. However, we have found that c-Cbl-mediated ubiquitination is required solely for degradation but not for internalization of the EGFR under oxidative stress. To further examine the fate of the EGFR under oxidative stress, we used confocal analysis to show that the receptor not only remains colocalized with caveolin-1 at the plasma membrane, but at longer time points, is also sorted to a perinuclear compartment via a clathrin-independent, caveolae-mediated pathway. Our findings indicate that although the EGFR associates with caveolin-1 constitutively, caveolin-1 is hyperphosphorylated only under oxidative stress, which is essential in transporting the EGFR to a perinuclear location, where it is not degraded and remains active. Thus, oxidative stress may have a role in tumorigenesis by not only activating the EGFR but also by promoting prolonged activation of the receptor both at the plasma membrane and within the cell. Activation of the epidermal growth factor (EGF)2 receptor (EGFR) by EGF results in the initiation of signal transduction cascades involved in cellular survival and proliferation. Therefore, to control cellular growth and tumorigenesis, the activation of the EGFR has to be tightly regulated in a process that includes degradation of the receptor. Binding of EGF to EGFR is rapidly followed by internalization of the membrane-bound receptor mainly through clathrin-coated pits and into early endosomes, which develop into late endosomes. There, the EGFR is either targeted to lysosomes for degradation or recycled to the plasma membrane (1-3). The inability of the EGFR to be down-regulated via clathrinmediated endocytosis and degradation has been linked to its oncogenicity (4, 5).H 2 O 2 -induced oxidative stress has been shown to activate and aberrantly phosphorylate the EGFR, which impedes the clathrin-mediated endocytosis and subsequent lysosomal degradation of the receptor (6 -8). This results in prolonged downstream activation of proliferative molecules such as Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) (9), and the lack of receptor turnover has been shown to mediate tumor promotion in non-neoplastic rat liver epithelial cells (10). To gain more insight into H 2 O 2 -induced EGFR signaling and hyperplastic responses, we examined the trafficking of the receptor under oxidative stress.Huang and Sorkin (11) have recently reported that knock-down of Grb2 by RNA interference inhibits clat...

Staphylococcus aureus causes pathologies ranging from minor skin infections to life-threatening diseases. Pathogenic effects are largely due to production of bacterial toxin, which is regulated by an RNA molecule, RNAIII. The S. aureus protein called RAP (RNAIII activating protein) activates RNAIII, and a peptide called RIP (RNAIII inhibiting peptide), produced by a nonpathogenic bacteria, inhibits RNAIII. Mice vaccinated with RAP or treated with purified or synthetic RIP were protected from S. aureus pathology. Thus, these two molecules may provide useful approaches for the prevention and treatment of diseases caused by S. aureus.

Staphylococcus aureus can cause disease through the production of toxins. Toxin production is autoinduced by the protein RNAIII-activating protein (RAP) and by the autoinducing peptide (AIP), and is inhibited by RNAIII-inhibiting peptide (RIP) and by inhibitory AIPs. RAP has been shown to be a useful vaccine target site, and RIP and inhibitory AIPs as therapeutic molecules to prevent and suppress S. aureus infections. Development of therapeutic strategies based on these molecules has been hindered by a lack of knowledge of the molecular mechanisms by which they activate or inhibit virulence. Here, we show that RAP specifically induces the phosphorylation of a novel 21-kDa protein, whereas RIP inhibits its phosphorylation. This protein was termed target of RAP (TRAP). The synthesis of the virulence regulatory molecule, RNAIII, is not activated by RAP in the trap mutant strain, suggesting that RAP activates RNAIII synthesis via TRAP. Phosphoamino acid analysis shows that TRAP is histidine-phosphorylated, suggesting that TRAP may be a sensor of RAP. AIPs upregulate the synthesis of RNAIII also in trap mutant strains, suggesting that TRAP and AIPs activate RNAIII synthesis via distinct signal transduction pathways. Furthermore, TRAP phosphorylation is down-regulated in the presence of AIP, suggesting that a network of signal transduction pathways regulate S. aureus pathogenesis.