O-GlcNAcylated p53 in the liver modulates hepatic glucose production.

p53 regulates several signaling pathways to maintain the metabolic homeostasis of cells and modulates the cellular response to stress. Deficiency or excess of nutrients causes cellular metabolic stress, and we hypothesized that p53 could be linked to glucose maintenance. We show here that upon starvation hepatic p53 is stabilized by O-GlcNAcylation and plays an essential role in the physiological regulation of glucose homeostasis. More specifically, p53 binds to PCK1 promoter and regulates its transcriptional activation, thereby controlling hepatic glucose production. Mice lacking p53 in the liver show a reduced gluconeogenic response during calorie restriction. Glucagon, adrenaline and glucocorticoids augment protein levels of p53, and administration of these hormones to p53 deficient human hepatocytes and to liver-specific p53 deficient mice fails to increase glucose levels. Moreover, insulin decreases p53 levels, and over-expression of p53 impairs insulin sensitivity. Finally, protein levels of p53, as well as genes responsible of O-GlcNAcylation are elevated in the liver of type 2 diabetic patients and positively correlate with glucose and HOMA-IR. Overall these results indicate that the O-GlcNAcylation of p53 plays an unsuspected key role regulating in vivo glucose homeostasis.

Adult Sox2+ stem cell exhaustion in mice results in cellular senescence and premature aging.

Aging is characterized by a gradual functional decline of tissues with age. Adult stem and progenitor cells are responsible for tissue maintenance, repair, and regeneration, but during aging, this population of cells is decreased or its activity is reduced, compromising tissue integrity and causing pathologies that increase vulnerability, and ultimately lead to death. The causes of stem cell exhaustion during aging are not clear, and whether a reduction in stem cell function is a cause or a consequence of aging remains unresolved. Here, we took advantage of a mouse model of induced adult Sox2+ stem cell depletion to address whether accelerated stem cell depletion can promote premature aging. After a short period of partial repetitive depletion of this adult stem cell population in mice, we observed increased kyphosis and hair graying, and reduced fat mass, all of them signs of premature aging. It is interesting that cellular senescence was identified in kidney after this partial repetitive Sox2+ cell depletion. To confirm these observations, we performed a prolonged protocol of partial repetitive depletion of Sox2+ cells, forcing regeneration from the remaining Sox2+ cells, thereby causing their exhaustion. Senescence specific staining and the analysis of the expression of genetic markers clearly corroborated that adult stem cell exhaustion can lead to cellular senescence induction and premature aging.

Silver Atomic Quantum Clusters of Three Atoms for Cancer Therapy: Targeting Chromatin Compaction to Increase the Therapeutic Index of Chemotherapy.

Nanomaterials with very low atomicity deserve consideration as potential pharmacological agents owing to their very small size and to their properties that can be precisely tuned with minor modifications to their size. Here, it is shown that silver clusters of three atoms (Ag3 -AQCs)-developed by an ad hoc method-augment chromatin accessibility. This effect only occurs during DNA replication. Coadministration of Ag3 -AQCs increases the cytotoxic effect of DNA-acting drugs on human lung carcinoma cells. In mice with orthotopic lung tumors, the coadministration of Ag3 -AQCs increases the amount of cisplatin (CDDP) bound to the tumor DNA by fivefold without modifying CDDP levels in normal tissues. As a result, CDDP coadministered with Ag3 -AQCs more strongly reduces the tumor burden. Evidence of the significance of targeting chromatin compaction to increase the therapeutic index of chemotherapy is now provided.

Transcriptional regulation of Sox2 by the retinoblastoma family of pocket proteins.

Cellular reprogramming to iPSCs has uncovered unsuspected links between tumor suppressors and pluripotency factors. Using this system, it was possible to identify tumor suppressor p27 as a repressor of Sox2 during differentiation. This led to the demonstration that defects in the repression of Sox2 can contribute to tumor development. The members of the retinoblastoma family of pocket proteins, pRb, p107 and p130, are negative regulators of the cell cycle with tumor suppressor activity and with roles in differentiation. In this work we studied the relative contribution of the retinoblastoma family members to the regulation of Sox2 expression. We found that deletion of Rb or p130 leads to impaired repression of Sox2, a deffect amplified by inactivation of p53. We also identified binding of pRb and p130 to an enhancer with crucial regulatory activity on Sox2 expression. Using cellular reprogramming we tested the impact of the defective repression of Sox2 and confirmed that Rb deficiency allows the generation of iPSCs in the absence of exogenous Sox2. Finally, partial depletion of Sox2 positive cells reduced the pituitary tumor development initiated by Rb loss in vivo. In summary, our results show that Sox2 repression by pRb is a relevant mechanism of tumor suppression.

Transcriptional repression of Bmp2 by p21(Waf1/Cip1) links quiescence to neural stem cell maintenance.

Relative quiescence and self renewal are defining features of adult stem cells, but their potential coordination remains unclear. Subependymal neural stem cells (NSCs) lacking cyclin-dependent kinase (CDK) inhibitor (CKI) 1a (p21) exhibit rapid expansion that is followed by their permanent loss later in life. Here we demonstrate that transcription of the gene encoding bone morphogenetic protein 2 (Bmp2) in NSCs is under the direct negative control of p21 through actions that are independent of CDK. Loss of p21 in NSCs results in increased levels of secreted BMP2, which induce premature terminal differentiation of multipotent NSCs into mature non-neurogenic astrocytes in an autocrine and/or paracrine manner. We also show that the cell-nonautonomous p21-null phenotype is modulated by the Noggin-rich environment of the subependymal niche. The dual function that we describe here provides a physiological example of combined cell-autonomous and cell-nonautonomous functions of p21 with implications in self renewal, linking the relative quiescence of adult stem cells to their longevity and potentiality.

p27(Kip1) directly represses Sox2 during embryonic stem cell differentiation.

The mechanisms responsible for the transcriptional silencing of pluripotency genes in differentiated cells are poorly understood. We have observed that cells lacking the tumor suppressor p27 can be reprogrammed into induced pluripotent stem cells (iPSCs) in the absence of ectopic Sox2. Interestingly, cells and tissues from p27 null mice, including brain, lung, and retina, present an elevated basal expression of Sox2, suggesting that p27 contributes to the repression of Sox2. Furthermore, p27 null iPSCs fail to fully repress Sox2 upon differentiation. Mechanistically, we have found that upon differentiation p27 associates to the SRR2 enhancer of the Sox2 gene together with a p130-E2F4-SIN3A repressive complex. Finally, Sox2 haploinsufficiency genetically rescues some of the phenotypes characteristic of p27 null mice, including gigantism, pituitary hyperplasia, pituitary tumors, and retinal defects. Collectively, these results demonstrate an unprecedented connection between p27 and Sox2 relevant for reprogramming and cancer and for understanding human pathologies associated with p27 germline mutations.

Resistance of neonatal primary astrocytes against Fas-induced apoptosis depends on silencing of caspase 8.

In the present report, we have found that primary fetal astrocytes express caspase 8 and undergo apoptosis in response to Fas ligation. In contrast, neonatal astrocytes do not express detectable levels of the enzyme and are resistant to Fas killing. Fas-induced apoptosis can be restored in these cells by up-regulation of caspase 8 expression by means of transient transfection with a caspase 8-encoding plasmid. Furthermore, treatment of primary astrocytes with the demethylating agent 5-Aza-dC restores caspase 8 expression and increases the sensibility of neonatal astrocytes to the cytotoxic effect of Fas activation. Altogether, our findings indicate that silencing of caspase 8 gene is a key factor controlling the outcome of neonatal astrocytes upon Fas engagement.

Desmoid tumors of the right rectus abdominus muscle in postpartum women.

BACKGROUND: Desmoid tumors are benign neoplasms that most often arise from muscle aponeurosis and have been associated with both trauma and pregnancy. The etiology of desmoids has not been determined. CLINICAL CHARACTERISTICS: We present here four almost identical cases with desmoids occurring in the same location, the right rectus abdominus muscle in young post partum females. All were over the age of 30 at the time of diagnosis. Three of them had previously used oral contraceptive agents for an average of 3 years. None had a history of trauma to the area of involvement. Three had early surgical resection and one was treated with tamoxifen and imatinib without response and then had surgical resection. DISCUSSION: All four patients are disease free at a median follow-up of 2.5 years. The possible etiology of desmoids tumors in this location in postpartum females is discussed.

Of mice without pockets: mouse models to study the function of Rb family proteins.

Three negative regulators of cell cycle, the related proteins, pRB, p107 and p130, constitute the family of pocket proteins. pRB is a tumor suppressor which has drawn a lot of attention on its family of proteins, with the ensuing intense study of their biology. As a result we have a wealth of information on their biochemistry and biology, ranging from their regulation to their biochemical activities, and the effects of their absence or overexpression on cells. Despite this, many questions remain unsolved. In recent years, analysis of genetically-modified mouse strains has provided interesting data regarding the physiological and pathophysiological roles of these three proteins. Specifically, germ-line and conditional knockout strains for one or more than one of the members of the family have revealed as powerful tools in this regard. Here we review the mouse models available for studying these cell cycle regulators and how data generated by these approaches have sometimes challenged previous thoughts about the pocket proteins biology.

TGF-beta-induced apoptosis in human thyrocytes is mediated by p27kip1 reduction and is overridden in neoplastic thyrocytes by NF-kappaB activation.

Millions of people worldwide suffer goiter, a proliferative disease of the follicular cells of the thyroid that may become neoplastic. Thyroid neoplasms have low proliferative index, low apoptotic index and a high incidence of metastasis. TGF-beta is overexpressed in thyroid follicular tumor cells. To investigate the role of TGF-beta in thyroid tumor progression, we established cultures of human thyrocytes from different proliferative pathologies (Grave's disease, multinodular goiter, follicular adenoma, papillary carcinoma), lymph node metastasis, and a normal thyroid sample. All cultures maintained the thyrocyte phenotype. TGF-beta induced cell-cycle arrest in all cultures, in contrast with results reported for other epithelial tumors. In deprived medium, TGF-beta induced apoptosis in normal thyrocyte cultures and all neoplastic cultures except the metastatic cultures. This apoptosis was mediated by a reduction in p27kip1 levels, inducing cell-cycle initiation. Antisense p27 expression induced apoptosis in the absence of TGF-beta. By contrast, in cells in which p27 was overexpressed, TGF-beta had a survival effect. In growth medium, a net survival effect occurs in neoplastic thyrocytes only, not normal thyrocytes, due to activation of the NF-kappaB survival program. Together, these findings suggest that (a) thyroid neoplasms are due to reduced apoptosis, not increased division, in line with the low proliferative index of these pathologies, and (b) TGF-beta induces apoptosis in normal thyrocytes via p27 reduction, but that in neoplastic thyrocytes this effect is overridden by activation of the NF-kappaB program.

p27 deficiency desensitizes Rb-/- cells to signals that trigger apoptosis during pituitary tumor development.

Low p27 expression in many human cancers is a prognostic indicator for poor outcome. While analysing the mechanism by which p27 deficiency contributed to tumor development in the Rb+/- mouse model, we identified a role for p27 as a proapoptotic tumor suppressor. We examined the cell cycle and apoptotic response of these pituitary tumor cells to the dopamine analog bromocriptine as well as the expression of Arf and other cell cycle and apoptotic regulators in these tumors. We also examined the expression of Arf and its function in mouse embryo fibroblasts either singly or doubly deficient for Rb and p27. From these studies, we concluded that the absence of p27 disabled the trigger for an Arf-dependent apoptotic response in Rb-/- tumor cells. This suggests a novel mechanism by which the loss of p27 may impact on tumor development.