The p53 protein is kept labile under normal conditions. This regulation is governed largely by its major negative regulator, Mdm2. In response to stress however, p53 accumulates and becomes activated. For this to occur, the inhibitory effects of Mdm2 have to be neutralized. Here we investigated the role of the promyelocytic leukemia protein (PML) in the activation of p53 in response to stress. We found that PML is critical for the accumulation of p53 in response to DNA damage under physiological conditions. PML protects p53 from Mdm2-mediated ubiquitination and degradation, and from inhibition of apoptosis. PML neutralizes the inhibitory effects of Mdm2 by prolonging the stress-induced phosphorylation of p53 on serine 20, a site of the checkpoint kinase 2 (Chk2). PML recruits Chk2 and p53 into the PML nuclear bodies and enhances p53/Chk2 interaction. Our results provide a novel mechanistic explanation for the cooperation between PML and p53 in response to DNA damage.

The predominant sand fly species collected inside houses in Kfar Adumim, an Israeli village in the Judean Desert that is a focus of cutaneous leishmaniasis, was Phlebotomus papatasi, which was also caught attempting to bite humans. Phlebotomus sergenti, which is rarely seen inside houses, constituted the predominant sand fly species in caves near the village. Leishmania isolates from Ph. sergenti and humans typed as Leishmania tropica. Sand fly and human isolates produced similar small nodular cutaneous lesions in hamsters. Isolates produced excreted factor (EF) of subserotypes A(9) or A(9)B(2), characteristic of L. tropica and reacted with L. tropica-specific monoclonal antibodies. Isoenzyme analysis consigned the strains to the L. tropica zymodemes MON-137 and MON-275. Molecular genetic analyses confirmed the strains were L. tropica and intraspecific microheterogeneity was observed. Genomic fingerprinting using a mini-satellite probe separated the L. tropica strains into two clusters that were not entirely congruent with geographic distribution. These results support the heterogeneous nature of L. tropica and incriminate Ph. sergenti as its vector in this Judean Desert focus.

The promyelocytic leukemia (PML) tumor suppressor is essential for the formation of PML nuclear bodies (NBs). PML and PMLNBs have been implicated in the regulation of growth inhibition, senescence and apoptosis. PML is activated in response to stress signals and is downregulated in certain human cancers. However, the factors mediating PML stability are incompletely understood. Here we demonstrate that a catalytically active form of the mammalian E3 ligase E6AP (HPV E6-associated protein) acts to reduce the half-life of the PML protein by promoting its degradation in the proteasome. E6AP mediates the ubiquitination of PML in an in vitro ubiquitination assay. E6AP and PML interact at physiological levels and colocalize in PML-NBs. Importantly, PML protein expression is elevated in multiple organs and cell types from E6AP null mice and in lymphoid cells is associated with increased number and intensity of PML-NBs. This PML elevation is enhanced in response to DNA damage. Our results identify E6AP as an important regulator of PML and PML-NBs. The promyelocytic leukemia (PML) tumor suppressor is implicated in the regulation of cell-cycle progression, premature senescence (triggered by oncogenic Ras) and apoptosis (reviewed by Bernardi and Pandolfi 1 ). Deregulation of PML can be oncogenic. PML-RARa contributes to acute promyelocytic leukemia (APL) 2,3 and downregulation of PML was observed in multiple human cancers. 4 PML knockout (KO) mice are resistant to lethal doses of ionizing irradiation (IR), and exhibit genomic instability and enhanced susceptibility to tumorigenesis upon exposure to carcinogens 1,5 or in the context of additional oncogenic events (e.g., a loss of Pten 6 ). The myriad of PML functions have been linked to its function in PML nuclear body (PML-NB) formation. 7 These are dynamic structures whose configuration and composition are modified in response to specific stress signals. 8 However, their mechanisms of action are only partially understood and are believed to be mediated by key proteins that are recruited to these structures, including pRb, SUMO, Daxx and p53. 9 The regulation of certain proteins, such as p53, is associated with the PML-NBs. 9 Stress stimuli that have been identified as activators of PML and PML-NBs include interferon (a and g), DNA damage, oncogenic stress and viral infection (reviewed in references 1,8,10 ). In contrast, exposure of cells to arsenic trioxide (As 2 O 3 ) or retinoic acid promotes PML degradation. 11 In contrast, the overexpression of specific cellular ubiquitin ligases, such as the Siah protein, 12 or certain viral ubiquitin ligases, such as the ICP0 regulatory protein of herpesvirus-1, 10 promotes the proteasomal degradation of PML and PML-RARa. However, the nature of the underlying mechanism of this degradation and whether it occurs under physiological conditions is not known. Recently, a function for CK2-mediated phosphorylation of PML (on serine 517) in the control of its protein stability was demonstrated. 13 In addition to phosphorylation, the covalen...

Upon exposure to DNA damage the p53 tumor suppressor is accumulated and activated to stall cellular growth. For this to occur, p53 must be relieved from its major inhibitors, Mdm2 (Hdm2 in humans) and Mdmx (Mdm4; Hdmx in humans). A key mechanism controlling this relief is the post-translational modifications of p53 and its inhibitors. We have previously demonstrated that the stress-activated tyrosine kinase, c-Abl, contributes to the relief of p53 from Hdm2. Because Hdmx is the major inhibitor of p53 activity, the additional possibility that c-Abl protects p53 through targeting Hdmx was explored in this study. c-Abl was found to interact with and to phosphorylate Hdmx. This phosphorylation was enhanced in response to DNA damage. Importantly, we mapped the sites of phosphorylation to the p53 binding domain of Hdmx. One of these phosphorylations, on tyrosine 99, inhibited Hdmx interaction with p53. This inhibition is consistent with the predicted role of this residue in the interaction with p53 based on the crystal structure of the interaction site. Our results show that c-Abl not only targets Hdm2, but also Hdmx, which together contribute to p53 activation in response to DNA damage.

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In human papillomavirus (HPV)-infected cells, the p53 tumor suppressor is tightly regulated by the HPV-E6-E6AP complex, which promotes it for proteasomal degradation. We previously demonstrated that c-Abl tyrosine kinase protects p53 from HPV-E6-E6AP complex-mediated ubiquitination and degradation under stress conditions. However, the underlying mechanism was not defined. In this study, we explored the possibility that c-Abl targets E6AP and thereby protects p53. We demonstrated that c-Abl interacts with and phosphorylates E6AP. We determined that the E3 ligase activity of E6AP is impaired in response to phosphorylation by c-Abl. We mapped the phosphorylation site to tyrosine 636 within the HECT catalytic domain of E6AP, and using substitution mutants, we showed that this residue dictates the E3 ligase activity of E6AP, in a substrate-specific manner. On the basis of the crystal structure of the HECT domain of E6AP, we propose a model in which tyrosine 636 plays a regulatory role in the oligomerization of E6AP, which is a process implicated in its E3 ubiquitin ligase activity. Our results suggest that c-Abl protects p53 from HPV-E6-E6AP complex-mediated degradation by phosphorylating E6AP and impairing its E3 ligase activity, thus providing a molecular explanation for the stress-induced protection of p53 in HPV-infected cells.

Treatment choice for patients with malaria in Israeli hospitals is based on microscopy and rapid diagnostic tests (RDTs). Here, we demonstrate the cumulative value of real-time polymerase chain reaction (PCR) in optimizing the treatment of malaria. Between January 2009 and December 2015, 451 samples from 357 patients were tested in our laboratory using a real-time PCR assay. Hospital laboratory results (without real-time PCR) were compared to those obtained in our laboratory. A total of 307 patients had a malaria-positive laboratory finding in the hospital. Out of those, 288 were confirmed positive and 19 negative using real-time PCR. Two negative hospital results were found to be positive by real-time PCR. More specifically, of 153 cases positive for Plasmodium falciparum by real-time PCR, only 138 (90%) had been correctly identified at the hospitals. Similarly, 66 (67%) of 99 cases positive for P. vivax, 2 (11%) of 18 cases positive for P. ovale, and 3 (30%) of 10 cases positive for P. malariae had been correctly identified. Of 10 cases of mixed infection, only one had been identified as such at the hospital. Thus, real-time PCR was required for correct identification in 81 (28%) out of 290 positive cases. In 52 (18%) of those, there was an erroneous categorization of relapsing versus non-relapsing parasites. In a nationwide study, we found that the use of real-time PCR is definitely beneficial and may change the decision regarding the choice of treatment.

We report seven cases of false-positive Plasmodium falciparum histidine-rich protein 2 (PfHRP2) malaria assay results in patients with acute schistosomiasis caused by Schistosoma mekongi. PfHRP2 assays were negative in travelers infected with Schistosoma mansoni or Schistosoma haematobium (n ‫؍‬ 13). Malaria was ruled out and rheumatoid factor was negative in all patients.