CHK2 stability is regulated by the E3 ubiquitin ligase SIAH2.

The serine threonine checkpoint kinase 2 (CHK2) is a critical protein involved in the DNA damage-response pathway, which is activated by phosphorylation inducing cellular response such as DNA repair, cell-cycle regulation or apoptosis. Although CHK2 activation mechanisms have been amply described, very little is known about degradation control processes. In the present study, we identify the ubiquitin E3 ligase SIAH2 as an interaction partner of CHK2, which mediates its ubiquitination and proteasomal degradation. CHK2 degradation is independent of both its activation and its kinase activity, but also of the phosphorylation in S456. We show that SIAH2-deficient cells present CHK2 accumulation together with lower ubiquitination levels. Accordingly, SIAH2 depletion by siRNA increases CHK2 levels. In response to DNA damage induced by etoposide, interaction between both proteins is disrupted, thus avoiding CHK2 degradation and promoting its stabilization. We also found that CHK2 phosphorylates SIAH2 at three residues (Thr26, Ser28 and Thr119), modifying its ability to regulate certain substrates. Cellular arrest in the G2/M phase induced by DNA damage is reverted by SIAH2 expression through the control of CHK2 levels. We observed that hypoxia decreases CHK2 levels in parallel to SIAH2 induction. Similarly, we provide evidence suggesting that resistance to apoptosis induced by genotoxic agents in cells subjected to hypoxia could be partly explained by the mutual regulation between both proteins. These results indicate that SIAH2 regulates CHK2 basal turnover, with important consequences on cell-cycle control and on the ability of hypoxia to alter the DNA damage-response pathway in cancer cells.

[Factors associated with early weaning in a Spanish region]. / Factores asociados al abandono precoz de la lactancia materna en una región del este de España.

INTRODUCTION: Breastfeeding has undoubtedly great benefits. Previous studies have foundan early dropout. Only a few studies have investigated related factors. Our aim was to find out on-going breastfeeding rates along the first 12 months after birth and analyse factors associated with early weaning. MATERIAL AND METHODS: This is a prospective study including consecutive pairs (mother and newborn) till completion of the required sample. Variables were collected performing a structured program of surveys to the mothers. Bivariate and multivariate analysis of the data was performed. RESULTS: A total of 452 pairs were recruited. It was found that 81% of them started breastfeeding, with a prevalence of breastfeeding of 39% and 21% at 3 and 6 months after birth, respectively. Factors associated with early discontinuation of breastfeeding were: pregnancy induced by assisted reproduction methods (OR=5.58; 95% CI: 2.62-11.91), maternal smoking (OR=1.56; 95% CI: 1.10-2.22), poor maternal expectations about the duration of breastfeeding (OR=2.19; 95% CI: 1.49-3.23), use of nipple shields for breastfeeding (OR=2.57; 95% CI: 1.69-3.90), pacifier use on a regular basis during the first month after delivery (OR=1.39; 95% CI: 1.02-1.91), maternal university educational level (OR=0,59; 95% CI: 0,40-0,88), attending birth preparation programs during pregnancy (OR=0,68; 95% CI: 0,49-0,94), and believing having enough milk output at the time of discharge (OR=0,66; 95% CI: 0,47-0,92). CONCLUSIONS: International recommendations about duration of breastfeeding are not achieved in our country because of high rates of early weaning. We describe the known factors involved and other novel factors. The implementation of interventions to increase breastfeeding rates and to prevent early weaning are strongly recommended.

Assessing medicinal plants from South-Eastern Spain for potential anti-inflammatory effects targeting nuclear factor-Kappa B and other pro-inflammatory mediators.

AIM OF THE STUDY: Identification of plants with anti-inflammatory activity can be successfully based on information gained through knowledge on their traditional use. This is particularly true for biodiversity-rich regions of the world such as the Mediterranean. While such approaches are often single target based, here we used a multitarget, cell-based approach focusing on the pro-inflammatory signaling cascade and especially the NF-kappaB (NF-kappaB) pathway. MATERIALS AND METHODS: The plants from South-Eastern Spain were chosen on the basis that they were recorded as having a traditional use against an indication related to inflammation. The primary target was the transcription factor NF-kappaB (using a luciferase-based assay in HeLa cells). In addition extracts were tested in vitro for effects on cytokines (IL-6, IL-8, TNF-alpha) or PGE(2) in monocytes and for potential cytotoxic/pro-apoptotic action as well as for their influence on the cell cycle. RESULTS: Overall, 64 medicinal plant drugs from 61 species were assessed as potential inhibitors of inflammatory mediators to levels of 100-10 microg/ml. Three plants showed the highest level of activity (50 microg/ml) in inhibiting the activation of NF-kappaB in 5.1 cells: Helichrysum stoechas (Asteraceae), Dorycnium pentaphyllum (Fabaceae, s.l.) and Phlomis almeriensis (Lamiaceae). In the tests against the cytokines it was particularly striking to find that a number of species, Bupleurum fruticosum, Chamaespartium tridentatum, Genista ramosissima, Helichrysum stoechas, Mercurialis tomentosa, Ononis ramosissima, Peganum harmala, Picnomon acarna, Retama sphaerocarpa and Santolina viscosa showed extracts that were active at inhibiting TNF-alpha (10 microg/ml). CONCLUSIONS: Overall, this project has identified a series of species with an activity profile which merits further phytochemical-pharmacological investigation.

Soluble dipeptidyl peptidase IV (CD-26) in serum of patients with colorectal carcinoma.

Dipeptidyl peptidase IV(DPPIV) or CD26 is a widely expressed ectopeptidase with functions in immune response such as the activation of T lymphocytes. It is expressed in the colon mucosal epithelium only when this becomes malignant. The aim of our study is to ascertain the soluble DPPIV/CD26 levels in the serum of patients with colorectal carcinoma, compared with the levels in healthy individuals. From an accrual of 70 healthy individuals and 99 patients diagnosed with colorectal adenocarcinoma, the levels of soluble DPPIV/CD26 were defined by colored enzymatic spectrophotometric response on the Gly-Pro-Paranitroaniline substrate. The patients diagnosed with colorectal cancer have a higher CD26 level than healthy subjects (p<0.05). Of these patients, those with metastatic colorectal disease have a significantly higher soluble CD26 level (p<0.01). It has also been found that patients with high LDH (lactatodeshidrogenase) and CEA (carcinoembrionary antigen) levels show higher CD26 levels (p<0.01) than patients with normal levels of such carcinoma markers.

Ingenol esters induce apoptosis in Jurkat cells through an AP-1 and NF-kappaB independent pathway.

BACKGROUND: Ingenol derivatives have received constant and multidisciplinary attention on account of their pleiotropic pattern of biological activity. This includes activation of protein kinase C (PKC), tumour-promotion, anticancer, and anti-HIV properties, and the possibility of dissecting co-cancerogenic and clinically useful activities has been demonstrated. Certain ingenol esters show powerful anticancer activity, and a structure-activity relationship model to discriminate between their apoptotic and non-apoptotic properties has been developed. RESULTS: The polyhydroxylated southern region of ingenol was selectively modified, using the anticancer and PKC activator ingenol 3,20-dibenzoate (IDB) as a lead compound. The evaluation of IDB analogues in apoptosis assays showed strict structure-activity relationships, benzoylation of the 20-hydroxyl being required to trigger apoptosis through a pathway involving caspase-3 and occurring at the specific cell cycle checkpoint that controls the S-M phase transition. Conversely, a study on the activation of the PKC-dependent transcription factors AP-1 and NF-kappaB by IDB analogues showed significant molecular flexibility, including tolerance to changes at the 3- and 20-hydroxyls. IDB-induced apoptosis was independent of activation of PKC, since it was not affected by treatment with the non-isoform-selective PKC inhibitor GF 109230X0. CONCLUSIONS: Remarkable deviations from the tumour-promotion pharmacophore were observed for both the apoptotic and the PKC-activating properties of IDB analogues, showing that ingenol is a viable template to selectively target crucial pathways involved in tumour promotion and development. Since the apoptotic and the PKC-activating properties of ingenoids are mediated by different pathways and governed by distinct structure-activity relationships, it is possible to dissect them by suitable chemical modification. In this context, the esterification pattern of the 5- and 20-hydroxyls is critical.

Phorboid 20-homovanillates induce apoptosis through a VR1-independent mechanism.

BACKGROUND: Vanilloids, such as capsaicin and resiniferatoxin (RTX), are recognized at the cell surface by vanilloid receptor type 1 (VR1), which has recently been cloned. VR1 mediates the effects of capsaicin and RTX in VR1-expressing cells, but vanilloids can induce apoptosis through a pathway not mediated by VR1. Phorboid 20-homovanillates can be used to investigate cell death induced by vanilloids. RESULTS: 12,13-Diacylphorbol-20 homovanillates were prepared by the sequential esterification of the natural polyol. Phorbol 12-phenylacetate 13-acetate 20-homovanillate (PPAHV) induced apoptosis in Jurkat cells to the same extent as RTX. Apoptosis was preceded by an increase in intracellular reactive oxygen species and by the loss of mitochondrial transmembrane potential. PPAHV-induced apoptosis was mediated by a pathway involving caspase-3 activation and was initiated at the S phase of the cell cycle. The cell-death pathway triggered by VR1 activation was studied in 293T cells transfected with the cloned rat vanilloid receptor. In this system, capsaicin and PPAHV induced cell death by an apparent necrotic mechanism, which was selectively inhibited by the competitive vanilloid receptor antagonist capsazepine. Interestingly, phorbol-12, 13-bisnonanoate-20-homovanillate, an analogue of PPAHV, induced cell death in VR1-transfected cells but could not trigger apoptosis in the Jurkat cell line. CONCLUSIONS: Vanilloids can induce cell death through different signalling pathways. The cell death induced in a VR1-independent manner has the hallmark of apoptosis, whereas the cell death mediated by vanilloids binding to VR1 is seemingly necrotic. Phorboid homovanillates that have antitumour and anti-inflammatory activities but lack the undesirable side effects of the natural vanilloids could be developed as potential drugs.

Hydroxyurea inhibits the transactivation of the HIV-long-terminal repeat (LTR) promoter.

HIV-1 gene expression is regulated by the promoter/enhancer located within the U3 region of the proviral 5' LTR that contains multiple potential cis-acting regulatory sites. Here we describe that the inhibitor of the cellular ribonucleoside reductase, hydroxyurea (HU), inhibited phorbol myristate acetate- or tumour necrosis factor-alpha-induced HIV-1-LTR transactivation in both lymphoid and non-lymphoid cells in a dose-dependent manner within the first 6 h of treatment, with a 50% inhibitory concentration of 0.5 mM. This inhibition was found to be specific for the HIV-1-LTR since transactivation of either an AP-1-dependent promoter or the CD69 gene promoter was not affected by the presence of HU. Moreover, gel-shift assays in 5.1 cells showed that HU prevented the binding of the NF-kappaB to the kappaB sites located in the HIV-1-LTR region, but it did not affect the binding of both the AP-1 and the Sp-1 transcription factors. By Western blots and cell cycle analyses we detected that HU induced a rapid dephosphorylation of the pRB, the product of the retinoblastoma tumour suppressor gene, and the cell cycle arrest was evident after 24 h of treatment. Thus, HU inhibits HIV-1 promoter activity by a novel pathway that implies an inhibition of the NF-kappaB binding to the LTR promoter. The present study suggests that HU may be useful as a potential therapeutic approach for inhibition of HIV-1 replication through different pathways.

Susceptibility of HIV-1-TAT transfected cells to undergo apoptosis. Biochemical mechanisms.

The effects of HIV-1 Tat protein on mitochondria membrane permeability and apoptosis were analysed in lymphoid cells. In this report we show that stable-transfected HIV-Tat cells are primed to undergo apoptosis upon serum withdrawal. This effect was observed in both the Jhan T cell line and the K562 cells, the latter expressing the bcr-abl chimeric gene, which confers resistance to apoptosis induced by different stimuli. Using a cytofluorimetric approach we have determined that serum withdrawal induces a disruption of the transmembrane mitochondrial potential (Deltapsim) followed by an increase of reactive oxygen species (ROS) and the subsequent DNA nuclear loss in K562-Tat cells but not in the K562-pcDNA cell line. These pre-apoptotic events were associated with the cleavage of the caspase-3, while the expression of Bcl-2, Bcl-XL and Bax proteins was not affected by the presence of Tat. Regardless of the steady state of the Bax protein, we found that in both K562 and K562-Tat cells, this protein is located in the nucleus, but after serum withdrawal its localization was mainly in the cytoplasm. The activity of caspase-3 detected in K562-Tat cells after serum withdrawal paralleled with the mitochondria permeability transition. Nevertheless, in Jhan-Tat cells the inhibition of this caspase with the specific inhibitor, z-DEVD-cmk, did not affect the disruption of the mitochondria potential induced by serum withdrawal. Interestingly, we found that HIV-Tat protein accumulates at the mitochondria in the K562-Tat cells cultured under low serum conditions, and this mitochondrial localization correlated with the Deltapsim disruption detected in these cells. In addition, HIV-1 Tat protein synergies with protoporphyrin IX (PPIX), a ligand of the mitochondrial benzodiazepine receptor, in the induction of apoptosis in both Jhan and K562 cells. Thus, HIV-1 Tat protein may induce apoptosis by a mechanism that involves mitochondrial PT and may contribute to the lymphocyte depletion seen in AIDS patients.

Selective induction of apoptosis by capsaicin in transformed cells: the role of reactive oxygen species and calcium.

Capsaicin is a vanilloid quinone analog that inhibits the plasma membrane electron transport (PMOR) system and induces apoptosis in transformed cells. Using a cytofluorimetric approach we have determined that capsaicin induces a rapid increase of reactive oxygen species (ROS) followed by a subsequent disruption of the transmembrane mitochondrial potential (DeltaPsim) and DNA nuclear loss in transformed cell lines and in mitogen activated human T cells. This apoptotic pathway is biochemically different from the typical one induced by either ceramide or edelfosine where, in our system, the DeltaPsim dissipation precedes the generation of reactive oxygen species. Neither production of ROS nor apoptosis was found in capsaicin-treated resting T cells where the activity of the PMOR system is minimal when compared with mitogen activated or transformed T cells. Capsaicin also induces Ca2+ mobilization in activated but not in resting T cells. However, preincubation of cells with BAPTA-AM, which chelate cytosolic free calcium, did not prevent ROS generation or apoptosis induced by capsaicin, suggesting that ROS generation in capsaicin treated cells is not a consequence of calcium signaling and that the apoptotic pathway may be separated from the one that mobilizes calcium. Moreover, we present data for the implication of a possible vanilloid receptor in calcium mobilization, but not in ROS generation. These results provide evidence that the PMOR system may be an interesting target to design antitumoral and anti-inflammatory drugs.