DNA damage causes TP53-dependent coupling of self-renewal and senescence pathways in embryonal carcinoma cells

Comment on: Wu R, et al. Clin Cancer Res 2011; 17:7359–72     

Wolframin deficiency is accompanied with metabolic inflexibility in rat striated muscles

The protein wolframin is localized in the membrane of the endoplasmic reticulum (ER), influencing Ca2+ metabolism and ER interaction with mitochondria, but the exact role of the protein remains unclear. Mutations in Wfs1 gene cause autosomal recessive disorder Wolfram syndrome (WS). The first symptom of the WS is diabetes mellitus, so accurate diagnosis of the disease as WS is often delayed. In this study we aimed to characterize the role of the Wfs1 deficiency on bioenergetics of muscles. Alterations in the bioenergetic profiles of Wfs1-exon-5-knock-out (Wfs1KO) male rats in comparison with their wild-type male littermates were investigated using high-resolution respirometry, and enzyme activity measurements. The changes were followed in oxidative (cardiac and soleus) and glycolytic (rectus femoris and gastrocnemius) muscles. There were substrate-dependent alterations in the oxygen consumption rate in Wfs1KO rat muscles. In soleus muscle, decrease in respiration rate was significant in all the followed pathways. The relatively small alterations in muscle during development of WS, such as increased mitochondrial content and/or increase in the OxPhos-related enzymatic activity could be an adaptive response to changes in the metabolic environment. The significant decrease in the OxPhos capacity is substrate dependent indicating metabolic inflexibility when multiple substrates are available.     

Morphological separation of aphid species <Emphasis Type="Italic">Cryptomyzus leonuri</Emphasis> Bozhko, 1961 and <Emphasis Type="Italic">Cryptomyzus alboapicalis</Emphasis> (Theobald, 1916) (Hemiptera: Sternorrhyncha: Aphididae)

Aphids of the species Cryptomyzus alboapicalis (Theobald, 1916) and Cryptomyzus leonuri Bozhko, 1961 are very similar morphologically, although exploit different host plants (Lamium album and Leonurus cardiaca, respectively). Morphological characters proposed for the separation of this species couple in the identification key to European Cryptomyzus species appeared to be of little discriminatory power when applied to apterous viviparous females from clonal lineages, whilst alate viviparous females of C. leonuri were not included in the key at all. The aim of this study was to find reliable morphological characters and their combinations for the separation of apterous and alate viviparous females of C. alboapicalis and C. leonuri. Forward stepwise discriminant analysis based on characters without statistically significant (P < 0.05) correlation (|r| ≥ 0.50) with body length resulted in canonical functions enabling correct classification of 95–100% of specimens from clonal lineages involved in the analysis with a priori specified group membership. The post hoc classification gave 95–100% correct identification of individuals from clonal and 85–100% from field-collected samples. The discriminative values of single morphological characters and canonical functions are discussed and modified key for the morphological identification of C. alboapicalis and C. leonuri apterous and alate viviparous females is suggested.     

Redox and metal ion binding properties of human insulin-like growth factor 1 determined by electrospray ionization mass spectrometry

Insulin-like growth factor 1 (IGF-1) is a 70-residue hormone containing three intramolecular disulfide bridges. IGF-1 and other growth factors are oxidatively folded in the endoplasmic reticulum and act primarily in the blood, under relatively oxidative conditions. It is known that IGF-1 exists in various intracellular and extracellular compartments in the oxidized form; however, the reduction potential of IGF-1 and the ability of fully reduced IGF-1, which contains six cysteine residues, to bind transition metal ions are not known. In this work, we determine that the redox potential of human IGF-1 is equal to -332 mV and the reduced form of hIGF-1 can bind cooperatively four Cu(+) ions, most probably into a tetracopper-hexathiolate cluster. The Cu(+) binding affinity of hIGF-1 is, however, approximately 3 times lower than that for the copper chaperones; thus, we can conclude that fully reduced hIGF-1 cannot compete with known Cu(+)-binding proteins.     

Mitotic catastrophe and endomitosis in tumour cells: an evolutionary key to a molecular solution

Following genotoxic insult, p53 mutated tumour cells undergo mitotic catastrophe. This is characterised by a switch from mitosis to the endocycle. The essential difference between mitosis and the endocycle is that in the latter, DNA synthesis is uncoupled from cell division, which leads to the formation of endopolyploid cells. Recent data suggests that a return from the endocycle into mitosis is also possible. Furthermore, our observations indicate that a particular type of endocycle known as endomitosis may be involved in this return. Here we review the role of endomitosis in the somatic reduction of polyploidy during development and its postulated role in the evolution of meiosis. Finally, we incorporate these evolutionary data to help interpret our most recent observations in the tumour cell system, which indicate a role for endomitosis and meiotic regulators, in particular p39mos in the segregation of genomes (somatic reduction) of these endopolyploid cells.     

Role of stress-activated OCT4A in the cell fate decisions of embryonal carcinoma cells treated with etoposide

Tumor cellular senescence induced by genotoxic treatments has recently been found to be paradoxically linked to the induction of “stemness.” This observation is critical as it directly impinges upon the response of tumors to current chemo-radio-therapy treatment regimens. Previously, we showed that following etoposide (ETO) treatment embryonal carcinoma PA-1 cells undergo a p53-dependent upregulation of OCT4A and p21Cip1 (governing self-renewal and regulating cell cycle inhibition and senescence, respectively). Here we report further detail on the relationship between these and other critical cell-fate regulators. PA-1 cells treated with ETO display highly heterogeneous increases in OCT4A and p21Cip1 indicative of dis-adaptation catastrophe. Silencing OCT4A suppresses p21Cip1, changes cell cycle regulation and subsequently suppresses terminal senescence; p21Cip1-silencing did not affect OCT4A expression or cellular phenotype. SOX2 and NANOG expression did not change following ETO treatment suggesting a dissociation of OCT4A from its pluripotency function. Instead, ETO-induced OCT4A was concomitant with activation of AMPK, a key component of metabolic stress and autophagy regulation. p16ink4a, the inducer of terminal senescence, underwent autophagic sequestration in the cytoplasm of ETO-treated cells, allowing alternative cell fates. Accordingly, failure of autophagy was accompanied by an accumulation of p16ink4a, nuclear disintegration, and loss of cell recovery. Together, these findings imply that OCT4A induction following DNA damage in PA-1 cells, performs a cell stress, rather than self-renewal, function by moderating the expression of p21Cip1, which alongside AMPK helps to then regulate autophagy. Moreover, this data indicates that exhaustion of autophagy, through persistent DNA damage, is the cause of terminal cellular senescence.