Physical activity and heart failure: a forgotten indicator

Introduction

Low physical activity may be associated with comorbidities, sedentary lifestyle or clinical worsening in heart failure (HF) patients. Cardiovascular implantable electronic devices (CIEDs) detect and analyse physical activity data that is often integrated in multifactorial algorithms for predicting HF decompensations, but its potential is probably underestimated.

Purpose

We hypothesized that low physical-activity levels, obtained from remote monitoring of CIEDs, help predict clinical outcomes in HF patients, independently from multifactorial algorithms.

Methods

We retrospectively evaluated consecutive patients with HF and CIEDs through clinical assessments and remote monitoring (two monitoring systems were used). Low activity was defined as <1 hour/day of physical activity and two groups of patients were defined: patients with low activity alerts (group 1) and patients without low activity alerts (group 2). Primary outcome was defined as death by all causes and secondary outcome as HF hospitalizations and sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) episodes.

Results

From 121 patients with RPM, physical activity data was obtained in 104 (85,9%). Mean age was 63,98±12,44 years, 70,2% were males and follow-up was 59,19±38,491 months. Fifty-four (51,9%) had implantable cardiac resynchronization therapy (CRT) defibrillator (CRT-D), 46 (44,2%) transvenous implantable cardioverter defibrillator (ICD), and 4 (3,8%) CRT pacemaker (CRT-P). The aetiology was idiopathic in 42,5% and ischemic in 40,2%. Mean left ventricular ejection fraction was 34,08±11,40% and mean physical activity duration was 2,25±1,84 hours/day. Forty-eight (53,7%) had low activity alerts (group 1) and 56 (46,3%) had no low activity alerts (group 2). In group 1 mean period of low activity was 52,978±15,75 days/year. Patients from group 1 were older (p=0,001), had more oncological disease (p=0,041) and peripheral artery disease (p=0,028). Three deaths occurred in total, all in group 1 (p=0,039) and HF hospitalizations were more frequent in group 1 (1,68±2,59 vs 0,69±1,32, p=0,005). Low activity burden was also associated with atrial fibrillation burden (r=0,473, p<0,05) and number of episodes of VT or VF (r=0,267, p=0,007). A decrease of 50% or more in mean duration of physical activity, but above 1 hour/day, was associated with increase HF hospitalizations (1,83±2,13 vs 1,05±1,95, p=0,006).

Conclusion

Low physical activity data obtained from CIEDs was associated with HF hospitalizations, arrhythmic events and death by all causes, independently of multifactorial algorithms. A decrease in basal activity even above alert threshold, was associated with HF hospitalizations and may be an even earlier sign of HF decompensations.

Funding Acknowledgement

Type of funding sources: None.

Lower rate limit in cardiac resynchronization therapy defibrillators

Background

There is few data about programmed lower rate limit (LRL) in real world heart failure (HF) patients with cardiac resynchronization therapy–defibrillators (CRT-Ds) and its influence in clinical outcomes. Heart rate score (HRS) is the percentage of all atrial-paced and sensed events in the single tallest 10 beats/min device histogram bin and may indicate impaired heart rate variability.

Purpose

We hypothesized that higher LRL programming is associated with worse clinical outcomes as arrhythmic events and HF decompensations in chronic HF patients with CRT-Ds.

Methods

LRL was evaluated and HRS was calculated from remote monitoring in 126 HF patients with CRT-D. Primary outcome was defined as HF hospitalizations and related admissions to the emergency department and secondary outcome as number of device therapies, sustained ventricular tachycardia (VT) and ventricular fibrillation (VF).

Results

Mean age was 69,03±10,39 years, 81 (64,3%) were males and mean follow-up was 53,72±46,13 months. Mean left ventricular ejection fraction was 30,31±8,33% and 29 (23,0%) were in NYHA III–IV. HF aetiology was idiopathic in 39 (43,3%), ischemic in 32 (25,4%) and alcoholic cardiomyopathy in 8 (6,3%). Thirty-seven (29,4%) patients had atrial fibrillation and 33 (26,2%) coronary disease. LRL ranged from to 40 to 80 bpm and mean LRL was 52,64±9,64 and mean HRS 49,60±23,17%. Programmed LRL was higher in women (p=0,014), patients with atrial fibrillation (AF) (p=0,012) and coronary disease (p=0,015). Higher LRL correlated with HF hospitalizations and related admissions to the emergency department (ED) (r=0,541, p=0,001), VT or VF episodes (r=0,337, p=0,005) and CRT-D number of therapies (r=0,342, p=0,004) and higher HRS (r=0,547, p<0,05).

Conclusion

Higher LRL programming was associated with higher HRS, HF decompensations with hospitalization or admission to the emergency department, VT or VF episodes and CRT-D therapies in a real world population. More studies are required but lower LRL may be preferred in HF patients.

Funding Acknowledgement

Type of funding sources: None.

Biventricular or left univentricular pacing in heart failure patients: is there a better strategy

Background

Cardiac resynchronization therapy (CRT) is a cornerstone in treatment of heart failure (HF) with reduced left ventricular ejection fraction (LVEF) and ventricular dyssynchrony. Biventricular (BiV) pacing is often the preferred method and corrects electrical and mechanical dyssynchrony but Left ventricular (LV) preferential pacing is may preserve conduction via the right bundle branch, preventing deleterious effects from right ventricular. The evidence is sparse and there is doubts whether which programming strategy is better.

Purpose

We hypothesized that BiV is non-inferior to preferential LV pacing in HF patients with reduced LVEF and CRT devices in cardiovascular death and HF hospitalizations.

Methods

We retrospectively evaluated 147 patients with HF patients with reduced LVEF and CRT devices. Two groups were defined: LV pacing (group 1) and BiV pacing (group 2). Primary outcome was defined as cardiovascular death and secondary outcome as HF hospitalizations and NYHA class after CRT.

Results

Mean age was 70,26±10,6 years, 68,1% were males and follow-up was 52,22±44,51 months. One hundred and twenty six (85,7%) patients had implantable cardiac resynchronization therapy (CRT) defibrillator (CRT-D) and 21 (14,3%) CRT pacemaker (CRT-P). Mean LVEF was 31,1±8,5% and mean QRS duration before CRT implantation was 149,5±48,6 ms. Thirty-nine (36,4%) patients were in NYHA III–IV. HF aetiology was idiopathic in 51 (47,2%), ischemic in 36 (33,3%) and alcoholic cardiomyopathy in 9 (8,3%). Forty-five (40,5%) patients had atrial fibrillation and 37 (35,6%) coronary disease. Patients in group 2 were more frequently males than group 1 patients (46 (78,0%) vs 32 (56,1%) respectively, p=0,012). There were no differences in regard to age, LVEF, HF aetiology or other comorbidities between groups. In 57 (49,1%) CRT was programming in preferential LV pacing and 50 (50,9%) in BiV pacing. There were 2 deaths in group 1 and 3 in group 2 (OR 0.80, 95% CI 0.27–2.40). There were 0,98±3,17 hospitalizations per patient and there were no differences in HF hospitalizations between groups (OR 1.01, 95% CI 0.92–1.18) or NYHA after 6 months of CRT (p=0,364).

Conclusion

BiV pacing was not inferior to LV-only pacing in regard to cardiovascular death, HF hospitalizations and NYHA class improvement. There was no clear advantage for one pacing strategy over the other but more studies are still required.

Funding Acknowledgement

Type of funding sources: None.

Suboptimal coronary flow after PCI in STEMI patients: clinical implications and predictors

Background

Even in experienced angioplasty centers, percutaneous coronary intervention (PCI) in the acute setting of ST-elevation myocardial infarctions (STEMI) is associated with a low, but still significant rate of suboptimal coronary flow. Identification of its clinical impact and potential modifiable risk factors is important.

Purpose

To evaluate the clinical impact of suboptimal coronary flow after PCI in STEMI patients and to access potential predictors of suboptimal coronary flow.

Methods

We retrospectively evaluated 103 hospitalized patients with acute STEMI who were admitted to our center between 2018 and 2019 and underwent PCI. Coronary flow was accessed using the Thrombolysis in myocardial infarction (TIMI) Flow Grading System. Patients were divided into suboptimal patency of the culprit-vessel, defined as TIMI flow ≤2 (group 1, n=8 (7,8%)) and optimal patency of the culprit-vessel defined as TIMI flow 3 (group 2, n=95 (92,2%)). Glomerular filtration rate (GFR) was calculated using the Modification of Diet in Renal Disease (MDRD) formula.

Results

Mean age 58,15±12,6 years and 85,4% were males. Seventy-eight patients (75,7%) had history of smoking, 45 (43,7%) dyslipidemia, 20 (19,4%) previous acute coronary syndrome, 18 (17,5%) diabetes, 17 (15,5%) were obese and 4 (3,9%) had chronic kidney disease. The revascularization strategy was primary PCI in 55 (54,4%) patients and fibrinolytic therapy with facilitated PCI in 48 (46,6%) patients. Infarct-related artery was the left anterior descending artery in 45 (45,5%) and multivessel disease was present in 38 (38,0%). Angiographic no-reflow after PCI was 3,0%. Intrahospital cardiovascular death occurred in 4 (3,9%) patients and was significantly associated with suboptimal flow (p=0,036) and there was no association with stent thrombosis. Predictors of suboptimal flow were higher blood urea nitrogen, creatinine and GFR at hospital admission (p=0,017 and p=0,012), peak creatinine (p=0,012) and stent length (p=0,038). Suboptimal flow was associated with higher Zwolle score (p=0,010) and ischemic Paris score (p=0,036).

Conclusion

Failure to achieve optimal culprit-vessel patency after PCI in STEMI patients, although infrequent, is associated with increased hospital cardiovascular death. Longer stents could be and important modified risk factor. Renal dysfunction is an important comorbidity that should be promptly identified and could be partially improved with medical treatment.

Funding Acknowledgement

Type of funding sources: None.

Fatty acids homeostasis during fasting predicts protection from chemotherapy toxicity

Fasting exerts beneficial effects in mice and humans, including protection from chemotherapy toxicity. To explore the involved mechanisms, we collect blood from humans and mice before and after 36 or 24 hours of fasting, respectively, and measure lipid composition of erythrocyte membranes, circulating micro RNAs (miRNAs), and RNA expression at peripheral blood mononuclear cells (PBMCs). Fasting coordinately affects the proportion of polyunsaturated versus saturated and monounsaturated fatty acids at the erythrocyte membrane; and reduces the expression of insulin signaling-related genes in PBMCs. When fasted for 24 hours before and 24 hours after administration of oxaliplatin or doxorubicin, mice show a strong protection from toxicity in several tissues. Erythrocyte membrane lipids and PBMC gene expression define two separate groups of individuals that accurately predict a differential protection from chemotherapy toxicity, with important clinical implications. Our results reveal a mechanism of fasting associated with lipid homeostasis, and provide biomarkers of fasting to predict fasting-mediated protection from chemotherapy toxicity.

Fasting has been reported to protect from chemotherapy-associated toxicity. Here, the authors show that fatty acid profiles in erythrocyte membranes and gene expression from peripheral blood mononuclear cells are associated to the fasting-mediated benefits during cancer treatment in mice and patients.

Conservation of Aging and Cancer Epigenetic Signatures across Human and Mouse

Aging and cancer are two interrelated processes, with aging being a major risk factor for the development of cancer. Parallel epigenetic alterations have been described for both, although differences, especially within the DNA hypomethylation scenario, have also been recently reported. Although many of these observations arise from the use of mouse models, there is a lack of systematic comparisons of human and mouse epigenetic patterns in the context of disease. However, such comparisons are significant as they allow to establish the extent to which some of the observed similarities or differences arise from pre-existing species-specific epigenetic traits. Here, we have used reduced representation bisulfite sequencing to profile the brain methylomes of young and old, tumoral and nontumoral brain samples from human and mouse. We first characterized the baseline epigenomic patterns of the species and subsequently focused on the DNA methylation alterations associated with cancer and aging. Next, we described the functional genomic and epigenomic context associated with the alterations, and finally, we integrated our data to study interspecies DNA methylation levels at orthologous CpG sites. Globally, we found considerable differences between the characteristics of DNA methylation alterations in cancer and aging in both species. Moreover, we describe robust evidence for the conservation of the specific cancer and aging epigenomic signatures in human and mouse. Our observations point toward the preservation of the functional consequences of these alterations at multiple levels of genomic regulation. Finally, our analyses reveal a role for the genomic context in explaining disease- and species-specific epigenetic traits.

Author Correction: Identification and characterization of Cardiac Glycosides as senolytic compounds

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Transient metabolic improvement in obese mice treated with navitoclax or dasatinib/quercetin

Senescent cells accumulate with obesity in the white adipose tissue of mice and humans. These senescent cells enhance the pro-inflammatory environment that, with time, contributes to the onset of glucose intolerance and type 2 diabetes. Glucose intolerance in mouse models of obesity has been successfully reversed by the elimination of senescent cells with the senolytic compounds navitoclax or the combination of dasatinib and quercetin (D/Q). In this work, we generated obese mice by high-fat diet feeding, and treated them with five consecutive cycles of navitoclax or D/Q during 16 weeks. We observed an efficient reduction in the white adipose tissue of the senescence markers senescence-associated β-galactosidase activity, Cdkn2a-p16 and Cdkn2a-p19 at the end of the 5 cycles. Mice treated with both navitoclax and D/Q showed an improvement of their insulin sensitivity and glucose tolerance during a short period of time (cycles 3 and 4), that disappeared at the fifth cycle. Also, these mice tended to increase the expression at their adipose tissue of the adipogenic genes Pparg and, Cebpa, as well as their plasma adiponectin levels. Together, our work shows that two different senolytic treatments, acting through independent pathways, are transiently effective in the treatment of obesity-induced metabolic disorders.

Sirt1 protects from K-Ras-driven lung carcinogenesis

The NAD+-dependent deacetylase SIRT1 can be oncogenic or tumor suppressive depending on the tissue. Little is known about the role of SIRT1 in non-small cell lung carcinoma (NSCLC), one of the deadliest cancers, that is frequently associated with mutated K-RAS Therefore, we investigated the effect of SIRT1 on K-RAS-driven lung carcinogenesis. We report that SIRT1 protein levels are downregulated by oncogenic K-RAS in a MEK and PI3K-dependent manner in mouse embryo fibroblasts (MEFs), and in human lung adenocarcinoma cell lines. Furthermore, Sirt1 overexpression in mice delays the appearance of K-RasG12V-driven lung adenocarcinomas, reducing the number and size of carcinomas at the time of death and extending survival. Consistently, lower levels of SIRT1 are associated with worse prognosis in human NSCLCs. Mechanistically, analysis of mouse Sirt1-Tg pneumocytes, isolated shortly after K-RasG12V activation, reveals that Sirt1 overexpression alters pathways involved in tumor development: proliferation, apoptosis, or extracellular matrix organization. Our work demonstrates a tumor suppressive role of SIRT1 in the development of K-RAS-driven lung adenocarcinomas in mice and humans, suggesting that the SIRT1-K-RAS axis could be a therapeutic target for NSCLCs.

Histone demethylase JMJD3 contributes to epigenetic control of INK4a/ARF by oncogenic RAS

The INK4a/ARF tumor suppressor locus, a key executor of cellular senescence, is regulated by members of the Polycomb group (PcG) of transcriptional repressors. Here we show that signaling from oncogenic RAS overrides PcG-mediated repression of INK4a by activating the H3K27 demethylase JMJD3 and down-regulating the methyltransferase EZH2. In human fibroblasts, JMJD3 activates INK4a, but not ARF, and causes p16(INK4a)-dependent arrest. In mouse embryo fibroblasts, Jmjd3 activates both Ink4a and Arf and elicits a p53-dependent arrest, echoing the effects of RAS in this system. Our findings directly implicate JMJD3 in the regulation of INK4a/ARF during oncogene-induced senescence and suggest that JMJD3 has the capacity to act as a tumor suppressor.

Normal cellular senescence and cancer susceptibility in mice genetically deficient in Ras-induced senescence-1 (Ris1)

Oncogenic Ras triggers a permanent cell-cycle arrest known as oncogene-induced senescence (OIS) that constitutes a relevant tumor suppressor mechanism. Ris1 (Ras-induced senescence-1) is a novel gene that was identified in a screen as specifically upregulated during Ras-induced senescence, and that is located at a chromosomal region, 3p21.3, frequently lost in human cancer. Moreover, Ris1 is highly conserved in vertebrates, does not present paralogs, and its sequence does not reveal similarities with other proteins or domains. To analyse the physiological function of Ris1 and test its putative role as a tumor suppressor gene, we have generated mutant mice deficient for this gene. Ris1-null mice are viable, fertile, develop normally and do not display any obvious abnormalities. Of relevance, Ris1-deficient mice had a normal lifespan and did not exhibit predisposition to spontaneous tumors or to tumors induced by chemical carcinogens. Finally, Ris1-deficient embryonic fibroblasts were indistinguishable from wild-type cells regarding their proliferation properties, immortalization, senescence and oncogenic transformation. These findings do not support a role of Ris1 in tumor suppression or in OIS.

Analysis of the candidate tumor suppressor Ris-1 in primary human breast carcinomas

Frequent chromosome 3 losses have been described in several tumors types, which strongly suggest the presence of one or several tumor suppressor genes. Recently, a novel candidate tumor suppressor gene termed Ris-1 (for Ras-induced senescence 1) has been identified at chromosomal position 3p21.3. Ris-1 has been proposed to participate in anti-tumor responses that resemble cellular senescence and that are elicited by oncogenes such as Ras. To analyze the role of Ris-1 as a putative tumor suppressor gene in human breast cancer, we have performed a real-time quantitative analysis of its mRNA expression in 60 patients. Moreover, we carried out a first approach to evaluate the most common inactivation mechanism that can affect expression levels of tumor suppressor genes (mutation, promoter hypermethylation and allelic losses). Furthermore, a correlation study between expression as well as inactivating mechanisms of Ris-1 and several clinico-pathological parameters of the tumors was designed, with the objective of appraising the prognostic value of Ris-1 status. Decreased expression of Ris-1 was observed in 23% of the cases and overexpressed Ris-1 was detected in 15% of the primary breast tumors. Our data showed high frequency of LOH (30%) at one of the markers used. Nevertheless, a polymorphism related with the expression levels was described. Statistically significant correlations were found between decreased Ris-1 expression and negative progesterone receptors, as well as between overexpressing Ris-1 tumors and high histological grade. Despite all these data, we conclude that the suggested role of Ris-1 as tumor suppressor gene is not evident, at least in breast cancer. Future and larger series studies in different tumor types are necessary to clarify Ris-1 function in human cancer.

Tumour biology: senescence in premalignant tumours

Oncogene-induced senescence is a cellular response that may be crucial for protection against cancer development, but its investigation has so far been restricted to cultured cells that have been manipulated to overexpress an oncogene. Here we analyse tumours initiated by an endogenous oncogene, ras, and show that senescent cells exist in premalignant tumours but not in malignant ones. Senescence is therefore a defining feature of premalignant tumours that could prove valuable in the diagnosis and prognosis of cancer.

Tumor induction by an endogenous K-ras oncogene is highly dependent on cellular context

We have targeted a K-ras allele in mouse embryonic stem (ES) cells to express a K-Ras(V12) oncoprotein along with a marker protein (beta-geo) from a single bicistronic transcript. Expression of this oncogenic allele requires removal of a knocked in STOP transcriptional cassette by Cre recombinase. Primary mouse embryonic fibroblasts expressing this K-ras(V12) allele do not undergo proliferative senescence and proliferate as immortal cells. In mice, expression of K-ras(V12) throughout the body fails to induce unscheduled proliferation or other growth abnormalities for up to eight months. Only a percentage of K-ras(V12)-expressing lung bronchiolo-alveolar cells undergo malignant transformation leading to the formation of multiple adenomas and adenocarcinomas. These results indicate that neoplastic growth induced by an endogenous K-ras oncogene depends upon cellular context.

Identification of a candidate tumor-suppressor gene specifically activated during Ras-induced senescence

Normal cells display protective responses against oncogenes. Notably, oncogenic Ras triggers an irreversible proliferation arrest that is reminiscent of replicative senescence and that is considered a relevant tumor-suppressor mechanism. Here, we have used microarrayed filters to identify genes specifically upregulated in Ras-senescent human fibroblasts. Among the initial set of genes selected from the microarrays, we found the cell-cycle inhibitor p21(Cip1/Waf1), thus validating the potency of the screening to identify markers and mediators of Ras-senescence. A group of six genes, formed by those more highly upregulated during Ras-senescence, was analyzed in further detail to evaluate their specificity. In particular, we examined their expression in cells overexpressing Ras but rendered resistant to Ras-senescence by the viral oncoprotein E1a; also, we have studied their expression during replicative senescence, organismal aging, H(2)O(2)-induced senescence, and DNA damage. In this manner, we have identified a novel gene, RIS1 (for Ras-induced senescence 1), which is not upregulated in association to any of the above-mentioned processes, but exclusively during Ras-senescence. Furthermore, RIS1 is also upregulated by the transcriptional factor Ets2, which is a known mediator of Ras-induced senescence. Interestingly, RIS1 is located at chromosomal position 3p21.3 and, more specifically, it is included in a short segment of just 1 Mb previously defined by other investigators for its tumor-suppressor activity. In summary, we report the identification of a novel gene, RIS1, as a highly specific marker of Ras-induced senescence and a candidate tumor-suppressor gene.

Effect of hypothyroidism on G protein-coupled receptor kinase 2 expression levels in rat liver, lung, and heart

GRK2 is a member of the G protein-coupled receptor kinase family that phosphorylates the activated form of beta-adrenergic and other G protein-coupled receptors and plays an important role in their desensitization and modulation. Alterations in thyroid hormone levels have been reported to lead to important changes in adrenergic receptor responsiveness and signaling in a variety of tissues. In this context, we have explored the effects of experimental hypothyroidism on GRK2 protein levels in rat heart, lung, and liver using a specific antibody. Hypothyroid animals show significant up-regulation ( approximately 50% increase compared with controls) in GRK2 levels in heart and lung at 60 days after birth, whereas a 50% reduction is detected in the liver at this stage. These alterations are selective, as beta-adrenergic receptors or other G protein-coupled receptor regulatory proteins, such as G protein-coupled receptor kinase 5 or beta-arrestin-1, display a different pattern of expression changes in the hypothyroid animals. The reported changes in GRK2 levels and in the receptor/kinase ratio predict alterations in adrenergic receptor desensitization and signal transduction efficacy consistent with those observed in thyroid disorders, thus suggesting a relevant role for the modulation of GRK2 expression in this physiopathological condition.

Inhibition of the phosphoinositide 3-kinase pathway induces a senescence-like arrest mediated by p27Kip1

A senescence-like growth arrest is induced in mouse primary embryo fibroblasts by inhibitors of phosphoinositide 3-kinase (PI3K). We observed that senescence-like growth arrest is correlated with an increase in p27(Kip1) but that down-regulation of other cyclin-dependent kinase (CDK) inhibitors, including p15(INK4b), p16(INK4a), p19( INK4d), and p21(Cip1) as well as other negative cell cycle regulators such as p53 and p19(ARF), implies that this senescence-related growth arrest is independent of the activity of p53, p19(ARF), p16(INK4a), and p21(Cip1), which are associated with replicative senescence. The p27(Kip1) binds to the cyclin/CDK2 complexes and causes a decrease in CDK2 kinase activity. We demonstrated that ectopic expression of p27(Kip1) can induce permanent cell cycle arrest and a senescence-like phenotype in wild-type mouse embryo fibroblasts. We also obtained results suggesting that the kinase inhibitors LY294002 and Wortmannin arrest cell growth and induce a senescence-like phenotype, at least partially, through inhibition of PI3K and protein kinase B/Akt, activation of the forkhead protein AFX, and up-regulation of p27(Kip1)expression. In summary, these observations taken together suggest that p27(Kip1) is an important mediator of the permanent cell cycle arrest induced by PI3K inhibitors. Our data suggest that repression of CDK2 activity by p27(Kip1) is required for the PI3K-induced senescence, yet mouse embryo fibroblasts derived from p27(Kip1-/-) mice entered cell cycle arrest after treatment with LY294002. We show that this is due to a compensatory mechanism by which p130 functionally substitutes for the loss of p27(Kip1). This is the first description that p130 may have a role in inhibiting CDK activity during senescence.

The downregulation of the pro-apoptotic protein Par-4 is critical for Ras-induced survival and tumor progression

Inhibition of apoptosis is an important characteristic of oncogenic transformation. The Par-4 gene product has recently been shown to be upregulated in cells undergoing apoptotic cell death, and its ectopic expression was shown to be critical in apoptosis. We demonstrate that expression of oncogenic Ras promotes a potent reduction of Par-4 protein and mRNA levels through a MEK-dependent pathway. In addition, the expression of permanently active mutants of MEK, Raf-1 or zetaprotein kinase C but not of phosphatidylinositol 3-kinase (PI 3-kinase) is sufficient to decrease Par-4 levels. These effects are independent of p53, p16 and p19, and were detected not only in fibroblast primary cultures but also in NIH 3T3 and HeLa cells, indicating that they are not secondary to Ras actions on cell cycle regulation. Importantly, restoration of Par-4 levels to normal in Ras-transformed cells makes these cells sensitive to the pro-apoptotic actions of tumor necrosis factor-alpha under conditions in which PI 3-kinase is inhibited and also severely impairs colony formation in soft agar and tumor development in nude mice, as well as increases the sensitivity of these tumors to camptothecin. This indicates that the downregulation of Par-4 by oncogenic Ras is a critical event in tumor progression.

Premature senescence involving p53 and p16 is activated in response to constitutive MEK/MAPK mitogenic signaling

Oncogenic Ras transforms immortal rodent cells to a tumorigenic state, in part, by constitutively transmitting mitogenic signals through the mitogen-activated protein kinase (MAPK) cascade. In primary cells, Ras is initially mitogenic but eventually induces premature senescence involving the p53 and p16(INK4a) tumor suppressors. Constitutive activation of MEK (a component of the MAPK cascade) induces both p53 and p16, and is required for Ras-induced senescence of normal human fibroblasts. Furthermore, activated MEK permanently arrests primary murine fibroblasts but forces uncontrolled mitogenesis and transformation in cells lacking either p53 or INK4a. The precisely opposite response of normal and immortalized cells to constitutive activation of the MAPK cascade implies that premature senescence acts as a fail-safe mechanism to limit the transforming potential of excessive Ras mitogenic signaling. Consequently, constitutive MAPK signaling activates p53 and p16 as tumor suppressors.

Adenosine diphosphate-degrading activity in placenta

1. The degradation of ADP by the placenta and umbilical artery was investigated. 2. Supernatants from incubations of finely chopped placental and umbilical arterial tissue were incubated with [14C]ADP for various durations from 0 to 30 min. 3. Products of ADP degradation were separated by thin-layer chromatography and radioactivity incorporated into each product was measured. 4. Placental supernatants induced a more rapid degradation of ADP than the umbilical artery supernatants. The main product of ADP degradation by placental supernatants at 30 min was adenosine, whereas that of umbilical artery was AMP. 5. This conversion by placenta of ADP, a potent platelet aggregator and vasoconstrictor, into adenosine, a potent platelet anti-aggregator and vasodilator, may be important in the maintenance of perfusion of the foetoplacental unit.