Frataxin participates to the hypoxia-induced response in tumors

Defective expression of frataxin is responsible for the degenerative disease Friedreich''s ataxia. Frataxin is a protein required for cell survival since complete knockout is lethal. Frataxin protects tumor cells against oxidative stress and apoptosis but also acts as a tumor suppressor. The molecular bases of this apparent paradox are missing. We therefore sought to investigate the pathways through which frataxin enhances stress resistance in tumor cells. We found that frataxin expression is upregulated in several tumor cell lines in response to hypoxic stress, a condition often associated with tumor progression. Moreover, frataxin upregulation in response to hypoxia is dependent on hypoxia-inducible factors expression and modulates the activation of the tumor-suppressor p53. Importantly, we show for the first time that frataxin is in fact increased in human tumors in vivo. These results show that frataxin participates to the hypoxia-induced stress response in tumors, thus implying that modulation of its expression could have a critical role in tumor cell survival and/or progression.     

Treatment with a BH3 mimetic overcomes the resistance of latency III EBV (+) cells to p53-mediated apoptosis

P53 inactivation is often observed in Burkitt''s lymphoma (BL) cells due to mutations in the p53 gene or overexpression of its negative regulator, murine double minute-2 (MDM2). This event is now considered an essential part of the oncogenic process. Epstein–Barr virus (EBV) is strongly associated with BL and is a cofactor in its development. We previously showed that nutlin-3, an antagonist of MDM2, activates the p53 pathway in BL cell lines harboring wild-type p53. However, nutlin-3 strongly induced apoptosis in EBV (−) or latency I EBV (+) cells, whereas latency III EBV (+) cells were much more resistant. We show here that this resistance to apoptosis is also observed in latency III EBV (+) lymphoblastoid cell lines. We also show that, in latency III EBV (+) cells, B-cell lymphona 2 (Bcl-2) is selectively overproduced and interacts with Bcl-2-associated X protein (Bax), preventing its activation. The treatment of these cells with the Bcl-2-homology domain 3 mimetic ABT-737 disrupts Bax/Bcl-2 interaction and allows Bax activation by nutlin-3. Furthermore, treatment with these two compounds strongly induces apoptosis. Thus, a combination of Mdm2 and Bcl-2 inhibitors might be a useful anti-cancer strategy for diseases linked to EBV infection.     

PTEN: a default gate-keeping tumor suppressor with a versatile tail

The tumor suppressor PTEN controls a variety of biological processes including cell proliferation, growth, migration, and death. As a master cellular regulator, PTEN itself is also subjected to deliberated regulation to ensure its proper function. Defects in PTEN regulation have a profound impact on carcinogenesis. In this review, we briefly discuss recent advances concerning PTEN regulation and how such knowledge facilitates our understanding and further exploration of PTEN biology. The carboxyl-tail of PTEN, which appears to be associated with multiple types of posttranslational regulation, will be under detailed scrutiny. Further, a comparative analysis of PTEN and p53 suggests while p53 needs to be activated to suppress tumorigenesis （a dormant gatekeeper）, PTEN is probably a constitutive surveillant against cancer development, thus a default gatekeeper.     

Downregulation of PTEN/MMAC/TEP1 expression in human prostate cancer cell line DU145 by growth stimuli

Genetic alterations and/or deletion of the tumor suppressor gene PTEN/MMAC/TEP1 occur in many types of human cancer including prostate cancer. We describe the production of monoclonal antibody against recombinant human PTEN and the study of PTEN gene and protein expression in three commercially available human prostate cancer cell lines, PC-3, LNCaP, and DU 145. Northern blotting analyses showed that LNCaP and DU145 but not PC-3 cells expressed PTEN mRNA. However, Western blotting analyses using a monoclonal antibody against PTEN demonstrated the expression of PTEN protein in DU145 but not LNCaP cells. In DU145 cells, PTEN expression at both the mRNA and protein levels inversely correlated with serum concentrations and levels of PKB/Akt phosphorylation. In addition, the basal activity of PKB/Akt as indicated by level of phosphorylation was higher in prostate cancer cells which do not express PTEN than that in the cells expressing wild type PTEN. Thus, PTEN may play a critical role in regulating cellular signaling in prostate cancer cells.     

In vivo analysis of mammary and non-mammary tumorigenesis in MMTV-cyclin D1 transgenic mice deficient in p53

Overexpression of the cyclin D1 oncogene and inactivation of the p53 tumor suppressor have both been implicated in substantial proportions of sporadic human breast cancers. Transgenic mice with cyclin D1 overexpression targeted to mammary tissue by the MMTV enhancer-promoter have been shown to develop mammary cancers. To investigate the relationship between pathways driven by cyclin D1 overexpression and p53 loss during the development of breast cancers, we crossed MMTV-cyclin D1 mice with p53 heterozygous null (p53^+/–) mice. In such crossed mice, cyclin D1-driven mammary neoplasia would need to be substantially accelerated by p53 loss in order for mammary tumors to develop prior to the expected onset of non-mammary tumors characteristic of the p53-deficient background alone. Instead, in mice heterozygous or homozygous for p53 deficiency and simultaneously carrying the MMTV-cyclin D1 transgene, only tumors typically found in p53-deficient mice developed and mammary tumors were not observed. Interestingly, MMTV-cyclin D1/p53^+/– mice appeared to develop these non-mammary tumors more rapidly than p53^+/– mice, and a majority of the sampled non-mammary tumors from MMTV-cyclin D1/p53^+/– mice showed ectopic expression of the MMTV-driven cyclin D1 transgene. Within the constraints of possible genetic background effects and limited sensitivity due to the early emergence of non-mammary tumors, these observations provide no evidence that inactivation of p53 confers a major additional selective advantage to mammary cells overexpressing cyclin D1 in this animal model of human breast cancer. Interestingly, the results do raise the possibility that p53 inactivation might complement or cooperate with cyclin D1 deregulation during the development of some types of non-mammary tumors.     

CDK4/6-inhibiting drug substitutes for p21 and p16 in senescence: Duration of cell cycle arrest and MTOR activity determine geroconversion

CDKN1A (p21) and CDKN2A (p16) inhibit CDK4/6, initiating senescence. According to our view on senescence, the role of p21 and p16 is to cause cell cycle arrest, whereas MTOR (mechanistic target of rapamycin) drives geroconversion to senescence. Recently we demonstrated that one of the markers of p21- and p16-initiated senescence is MEK-dependent hyper-elevation of cyclin D1. We noticed that a synthetic inhibitor of CDK 4/6 (PD0332991) also induced cyclin D1-positive senescence. We demonstrated that PD0332991 and p21 caused almost identical senescence phenotypes. p21, p16, and PD0332991 do not inhibit MTOR, and rapamycin decelerates geroconversion caused by all 3 molecules. Like p21, PD0332991 initiated senescence at any concentration that inhibited cell proliferation. This confirms the notion that a mere arrest in the presence of active MTOR may lead to senescence.     

Recurrent gain-of-function USP8 mutations in Cushing's disease

Cushing''s disease, also known as adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas (PAs) that cause excess cortisol production, accounts for up to 85% of corticotrophin-dependent Cushing''s syndrome cases. However, the genetic alterations in this disease are unclear. Here, we performed whole-exome sequencing of DNA derived from 12 ACTH-secreting PAs and matched blood samples, which revealed three types of somatic mutations in a candidate gene, USP8 (encoding ubiquitin-specific protease 8), exclusively in exon 14 in 8 of 12 ACTH-secreting PAs. We further evaluated somatic USP8 mutations in additional 258 PAs by Sanger sequencing. Targeted sequencing further identified a total of 17 types of USP8 variants in 67 of 108 ACTH-secreting PAs (62.04%). However, none of these mutations was detected in other types of PAs (n = 150). These mutations aggregate within the 14-3-3 binding motif of USP8 and disrupt the interaction between USP8 and 14-3-3 protein, resulting in an elevated capacity to protect EGFR from lysosomal degradation. Accordingly, PAs with mutated USP8 display a higher incidence of EGFR expression, elevated EGFR protein abundance and mRNA expression levels of POMC, which encodes the precursor of ACTH. PAs with mutated USP8 are significantly smaller in size and have higher ACTH production than wild-type PAs. In surgically resected primary USP8-mutated tumor cells, USP8 knockdown or blocking EGFR effectively attenuates ACTH secretion. Taken together, somatic gain-of-function USP8 mutations are common and contribute to ACTH overproduction in Cushing''s disease. Inhibition of USP8 or EGFR is promising for treating USP8-mutated corticotrophin adenoma. Our study highlights the potentially functional mutated gene in Cushing''s disease and provides insights into the therapeutics of this disease.     

Radiation-induced breast cancer in women with Hodgkin's disease

Aim and background

The aim of this study is to analyze the main clinical and pathologic characteristics of radiation-induced breast carcinomas (BC) following treatment for Hodgkin''s disease (HD) and to identify the risk factors for their induction. To create a mathematical model for the prediction of expected age at which a BC might develop based on the age at treatment for HD.

Materials and methods

Thirty-nine cases of women with BC that developed after treatment for HD in puberty or adolescence were analyzed retrospectively. The median age at initiation of treatment for HD was 12.9 years (9–21). The median age at diagnosis of the second malignancy – breast carcinoma was 32.4 years (22.9–39).

Results

The distribution of patients according to the clinical T stage of breast cancer was as follows: 11 patients with T1 stage BC (28%), 22 with T2 stage (56%) and 6 with stage T3 (16%). Prevalent were tumors localized in the lateral breast quadrants. The observed 5 year survival was 95%.

Conclusion

The risk of solid tumors, especially breast cancer, is high among women with HD disease who were treated with radiotherapy in their childhood. In this article, we propose a specific mathematical age formula which could be used as predictive equation when the age of the treatment for HD is in the range between 9 and 21 years. Systematic screening for breast cancer in these patients would be significantly important for their health and could improve their survival.     

Size,longevity and cancer: age structure

There is significant recent interest in Peto''s paradox and the related problem of the evolution of large, long-lived organisms in terms of cancer robustness. Peto''s paradox refers to the expectation that large, long-lived organisms have a higher lifetime cancer risk, which is not the case: a paradox. This paradox, however, is circular: large, long-lived organisms are large and long-lived because they are cancer robust. Lifetime risk, meanwhile, depends on the age distributions of both cancer and competing risks: if cancer strikes before competing risks, then lifetime risk is high; if not, not. Because no set of competing risks is generally prevalent, it is instructive to temporarily dispose of competing risks and investigate the pure age dynamics of cancer under the multistage model of carcinogenesis. In addition to augmenting earlier results, I show that in terms of cancer-free lifespan large organisms reap greater benefits from an increase in cellular cancer robustness than smaller organisms. Conversely, a higher cellular cancer robustness renders cancer-free lifespan more resilient to an increase in size. This interaction may be an important driver of the evolution of large, cancer-robust organisms.     

Type 2 diabetes mellitus: An unusual association with Down's syndrome

Down''s syndrome (DS) is known to be associated with autoimmune disease including type 1 diabetes. To the best of our knowledge, there are no reports of DS with type 2 diabetes mellitus in the literature. We hereby report two cases of DS with type 2 diabetes.     

The multiple facets of Peto's paradox: a life-history model for the evolution of cancer suppression

Large animals should have higher lifetime probabilities of cancer than small animals because each cell division carries an attendant risk of mutating towards a tumour lineage. However, this is not observed—a (Peto''s) paradox that suggests large and/or long-lived species have evolved effective cancer suppression mechanisms. Using the Euler–Lotka population model, we demonstrate the evolutionary value of cancer suppression as determined by the ‘cost’ (decreased fecundity) of suppression verses the ‘cost’ of cancer (reduced survivorship). Body size per se will not select for sufficient cancer suppression to explain the paradox. Rather, cancer suppression should be most extreme when the probability of non-cancer death decreases with age (e.g. alligators), maturation is delayed, fecundity rates are low and fecundity increases with age. Thus, the value of cancer suppression is predicted to be lowest in the vole (short lifespan, high fecundity) and highest in the naked mole rat (long lived with late female sexual maturity). The life history of pre-industrial humans likely selected for quite low levels of cancer suppression. In modern humans that live much longer, this level results in unusually high lifetime cancer risks. The model predicts a lifetime risk of 49% compared with the current empirical value of 43%.     

The Parkinson's disease protein LRRK2 impairs proteasome substrate clearance without affecting proteasome catalytic activity

Leucine-rich repeat kinase 2 (LRRK2) mutations are the most common known cause of Parkinson''s disease (PD). The clinical features of LRRK2 PD are indistinguishable from idiopathic PD, with accumulation of α-synuclein and/or tau and/or ubiquitin in intraneuronal aggregates. This suggests that LRRK2 is a key to understanding the aetiology of the disorder. Although loss-of-function does not appear to be the mechanism causing PD in LRRK2 patients, it is not clear how this protein mediates toxicity. In this study, we report that LRRK2 overexpression in cells and in vivo impairs the activity of the ubiquitin-proteasome pathway, and that this accounts for the accumulation of diverse substrates with LRRK2 overexpression. We show that this is not mediated by large LRRK2 aggregates or sequestration of ubiquitin to the aggregates. Importantly, such abnormalities are not seen with overexpression of the related protein LRRK1. Our data suggest that LRRK2 inhibits the clearance of proteasome substrates upstream of proteasome catalytic activity, favouring the accumulation of proteins and aggregate formation. Thus, we provide a molecular link between LRRK2, the most common known cause of PD, and its previously described phenotype of protein accumulation.     

Effect of amyloids on the vesicular machinery: implications for somatic neurotransmission

Certain neurodegenerative diseases are thought to be initiated by the aggregation of amyloidogenic proteins. However, the mechanism underlying toxicity remains obscure. Most of the suggested mechanisms are generic in nature and do not directly explain the neuron-type specific lesions observed in many of these diseases. Some recent reports suggest that the toxic aggregates impair the synaptic vesicular machinery. This may lead to an understanding of the neuron-type specificity observed in these diseases. A disruption of the vesicular machinery can also be deleterious for extra-synaptic, especially somatic, neurotransmission (common in serotonergic and dopaminergic systems which are specifically affected in Alzheimer''s disease (AD) and Parkinson''s disease (PD), respectively), though this relationship has remained unexplored. In this review, we discuss amyloid-induced damage to the neurotransmitter vesicular machinery, with an eye on the possible implications for somatic exocytosis. We argue that the larger size of the system, and the availability of multi-photon microscopy techniques for directly visualizing monoamines, make the somatic exocytosis machinery a more tractable model for understanding the effect of amyloids on all types of vesicular neurotransmission. Indeed, exploring this neglected connection may not just be important, it may be a more fruitful route for understanding AD and PD.