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Simple Summary Neuroendocrine lung tumors are a heterogeneous group of malignancies that share a common neuroendocrine nature. They range from low- and intermediate-grade typical and atypical carcinoma, to the highly malignant large cell neuroendocrine lung carcinoma and small cell carcinoma, with marked differences in incidences and prognosis. This review delineates the current knowledge of the genetic landscape of the human tumors, its influence in the development of genetically engineered mouse models (GEMMs) and the molecular imaging tools available to detect and monitor these diseases. While small cell lung carcinoma is one of the diseases best represented by GEMMs, there is a worrying lack of animal models for the other members of the group, these being understudied diseases. Regardless of the incidence and material available, they all are in urgent need of effective therapies. Abstract Neuroendocrine lung tumors comprise a range of malignancies that extend from benign tumorlets to the most prevalent and aggressive Small Cell Lung Carcinoma (SCLC). They also include low-grade Typical Carcinoids (TC), intermediate-grade Atypical Carcinoids (AC) and high-grade Large Cell Neuroendocrine Carcinoma (LCNEC). Optimal treatment options have not been adequately established: surgical resection when possible is the choice for AC and TC, and for SCLC chemotherapy and very recently, immune checkpoint inhibitors. Some mouse models have been generated based on the molecular alterations identified in genomic analyses of human tumors. With the exception of SCLC, there is a limited availability of (preclinical) models making their development an unmet need for the understanding of the molecular mechanisms underlying these diseases. For SCLC, these models are crucial for translational research and novel drug testing, given the paucity of human material from surgery. The lack of early detection systems for lung cancer point them out as suitable frameworks for the identification of biomarkers at the initial stages of tumor development and for testing molecular imaging methods based on somatostatin receptors. Here, we review the relevant models reported to date, their impact on the understanding of the biology of the tumor subtypes and their relationships, as well as the effect of the analyses of the genetic landscape of the human tumors and molecular imaging tools in their development.

IKKβ (encoded by IKBKB) is a protein kinase that regulates the activity of numerous proteins important in several signaling pathways, such as the NF-κB pathway. IKKβ exerts a protumorigenic role in several animal models of lung, hepatic, intestinal, and oral cancer. In addition, genomic and proteomic studies of human tumors also indicate that IKBKB gene is amplified or overexpressed in multiple tumor types. Here, the relevance of IKKβ in skin cancer was determined by performing carcinogenesis studies in animal models overexpressing IKKβ in the basal skin layer. IKKβ overexpression resulted in a striking resistance to skin cancer development and an increased expression of several tumor suppressor proteins, such as p53, p16, and p19. Mechanistically, this skin tumor–protective role of IKKβ is independent of p53, but dependent on the activity of the Ink4a/Arf locus. Interestingly, in the absence of p16 and p19, IKKβ-increased expression favors the appearance of cutaneous spindle cell–like squamous cell carcinomas, which are highly aggressive tumors. These results reveal that IKKβ activity prevents skin tumor development, and shed light on the complex nature of IKKβ effects on cancer progression, as IKKβ can both promote and prevent carcinogenesis depending on the cell type or molecular context. Implications: The ability of IKKβ to promote or prevent carcinogenesis suggests the need for further evaluation when targeting this protein. Mol Cancer Res; 15(9); 1255–64. ©2017 AACR.

The annexin protein superfamily has been implicated in multiple physiological and pathological processes, including carcinogenesis. Altered expression of various annexins has frequently been observed and linked to the development and progression of various human malignancies. However, information is lacking on the expression and clinical significance of annexin A9 (ANXA9) and A10 (ANXA10) in head and neck squamous cell carcinomas (HNSCC). ANXA9 and ANXA10 expression was evaluated in a large cohort of 372 surgically treated HPV-negative HNSCC patients and correlated with the clinicopathologic parameters and disease outcomes. Down-regulation of ANXA9 expression was found in 42% of HNSCC tissue samples, compared to normal epithelia. ANXA9 expression in tumors was significantly associated with oropharyngeal location and histological differentiation grade (P &lt, 0.001). In marked contrast, ANXA10 expression was absent in normal epithelium, but variably detected in the cytoplasm of cancer cells. Positive ANXA10 expression was found in 64% of tumors, and was significantly associated with differentiation grade (P &lt, 0.001), being also more frequent in oropharyngeal tumors (P = 0.019). These results reveal that the expression of both ANXA9 and ANXA10 is frequently altered in HNSCC and associated to the tumor differentiation grade, suggesting that they could be implicated in the pathogenesis of these cancers.

Hair follicle stem cells (HF-SCs) alternate between periods of quiescence and proliferation, to finally differentiate into all the cell types that constitute the hair follicle. Also, they have been recently identified as cells of origin in skin cancer. HF-SCs localize in a precise region of the hair follicle, the bulge, and molecular markers for this population have been established. Thus, HF-SCs are good model to study the potential role of oncogenic activations on SC physiology. Expression of a permanently active form of Akt (myrAkt) in basal cells leads to Akt hyperactivation specifically in the CD34+Itga6H population. This activation causes bulge stem cells to exit from quiescence increasing their response to proliferative stimuli and affecting some functions such as cell migration. HF-SC identity upon Akt activation is preserved; in this sense, increased proliferation does not result in stem cell exhaustion with age suggesting that Akt activation does not affect self-renewal an important aspect for normal tissue maintenance and cancer development. Genome-wide transcriptome analysis of HF-SC isolated from myrAkt and wild-type epidermis underscores changes in metabolic pathways characteristic of cancer cells. These differences manifest during a two-step carcinogenesis protocol in which Akt activation in HF-SCs results in increased tumor development and malignant transformation. Stem Cells 2014;32:1917–1928

This article is distributed under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License., Observations in thyroid patients and experimental animals show that the skin is an important target for the thyroid hormones. We previously showed that deletion in mice of the thyroid hormone nuclear receptors TRα1 and TRβ (the main thyroid hormone-binding isoforms) results in impaired epidermal proliferation, hair growth, and wound healing. Stem cells located at the bulges of the hair follicles are responsible for hair cycling and contribute to the regeneration of the new epidermis after wounding. Therefore a reduction in the number or function of the bulge stem cells could be responsible for this phenotype. Bulge cells show increased levels of epigenetic repressive marks, can retain bromodeoxyuridine labeling for a long time, and have colony-forming efficiency (CFE) in vitro. Here we demonstrate that mice lacking TRs do not have a decrease of the bulge stem cell population. Instead, they show an increase of label-retaining cells (LRCs) in the bulges and enhanced CFE in vitro. Reduced activation of stem cells leading to their accumulation in the bulges is indicated by a strongly reduced response to mobilization by 12-O-tetradecanolyphorbol-13-acetate. Altered function of the bulge stem cells is associated with aberrant activation of Smad signaling, leading to reduced nuclear accumulation of β-catenin, which is crucial for stem cell proliferation and mobilization. LRCs of TR-deficient mice also show increased levels of epigenetic repressive marks. We conclude that thyroid hormone signaling is an important determinant of the mobilization of stem cells out of their niche in the hair bulge. These findings correlate with skin defects observed in mice and alterations found in human thyroid disorders., This work was supported by grants from the Ministerio de Economía y Competitividad (BFU2011-28058 to A.A. and SAF2012-34378 to J.M.P.), the Instituto de Salud Carlos III (RD12 /0036/0030 to A.A. and RD12/0036/0009 to J.M.P.), and the Comunidad de Madrid (S2011/BMD-2328 TIRONET to A.A. and S2010/BMD-2470 to J.M.P.).

Fas-associated death domain (FADD) is an adaptor protein that is required for the transmission of the death signal from lethal receptors of the tumor necrosis factor superfamily. FADD contains a death domain (DD) and a death effector domain (DED). As death receptors contribute to renal tubular injury and tubular cell FADD increases in acute renal failure, we have studied the function of FADD in tubular epithelium. FADD expression was studied in kidney samples from mice. In order to study the contribution of FADD to renal tubular cell survival, FADD or FADD-DD were overexpressed in murine tubular epithelium. FADD is expressed in renal tubules of the healthy kidney. Both FADD and FADD-DD induce apoptosis in primary cultures of murine tubular epithelium and in the murine cortical tubular cell line. Death induced by FADD-DD has apoptotic morphology, but differs from death receptor-induced apoptosis in that it is not blocked by inhibitors of caspases. Neither an inhibitor of serine proteases nor overexpression of antiapoptotic BclxL prevented cell death. However, the combination of caspase and serine protease inhibition was protective. FADD and FADD-DD overexpression decreased nuclear factor kappa B activity. These data suggest that FADD has a death regulatory function in renal tubular cells that is independent of death receptors. FADD-DD is sufficient to induce apoptosis in these cells. This information is relevant to understanding the role of FADD in tubular injury.

Recent research has shown that apoptosis and its regulatory mechanisms contribute to cell number regulation in acute renal failure. Acute tubular necrosis is the most frequent form of parenchymal acute renal failure. The main causes are ischemia-reperfusion, sepsis and nephrotoxic drugs. Exogenous factors such as nephrotoxic drugs and bacterial products, and endogenous factors such as lethal cytokines promote tubular cell apoptosis. Such diverse stimuli engage intracellular death pathways that in some cases are stimulus-specific. We now review the role of apoptosis in acute renal failure, the potential molecular targets of therapeutic intervention, the therapeutic weapons to modulate the activity of these targets and the few examples of therapeutic intervention on apoptosis.

Cell number abnormalities are frequent in renal diseases, and range from the hypercellularity of postinfectious glomerulonephritis to the cell depletion of chronic renal atrophy. Recent research has shown that apoptosis and its regulatory mechanisms contribute to cell number regulation in the kidney. The role of apoptosis ranges from induction to repair and progression of renal injury. Death ligands and receptors, such as TNF and FasL, proapoptotic and antiapoptotic Bcl-2 family members and caspases have all been shown to participate in apoptosis regulation in the course of renal injury. These proteins represent potential therapeutic targets, which should be further explored.

Fas ligand (FasL) is a cell membrane cytokine that can promote apoptosis through activation of Fas receptors. Fas receptor activation induces glomerular cell apoptosis in vivo and participates in tubular cell death during acute renal failure. However, there is little information on the expression of FasL in the kidney. This study reports that FasL mRNA and protein are present in normal mouse and rat kidney. In situ hybridization and immunohistochemistry showed that proximal tubular epithelium is the main site of FasL expression in the normal kidney. In addition, increased total kidney FasL mRNA and de novo FasL protein expression by glomerular cells were observed in two different models of glomerular injury : rat immune-complex proliferative glumerulonephritis and murine lupus nephritis. Both full-length and soluble FasL were increased in the kidneys of the mice with nephritis. Cultured murine proximal tubular epithelial MCT cells and primary cultures of murine tubular epithelial cells expressed FasL mRNA and protein. Tubular epithelium-derived FasL induced apoptosis in Fassensitive lymphoid cell lines but not in Fas-resistant lymphoid cell lines. By contrast, MCT cells grown in the presence of the survival factors of serum were resistant to FasL, and only became partially sensitive to apoptosis induced by high concentrations (100 ng/ml) of FasL upon serum deprivation. However, MCT cells stimulated with inflammatory mediators (tumor necrosis factor-alpha, interferon-gamma, and lipopolysaccharide) increased cell surface Fas expression and were sensitized to apoptosis induced by FasL (FasL 55 +/- 5% versus control 8.3 +/- 4.1% apoptotic cells at 24 h, P0.05). Cytokine-primed primary cultures of tubular epithelial cells also acquired sensitivity to FasL-induced apoptosis. These results suggest that FasL expression by intrinsic renal cells may play a role in cell homeostasis in the normal kidney and during renal injury.

Expression of apoptosis regulatory proteins in tubular epithelium stressed in culture or following acute renal failure.BackgroundWhile tubular cell death is a characteristic of acute renal failure (ARF), the molecular mechanisms that modulate this cell death are unclear. Cell fate in acute renal failure hinges on a balance of survival and mortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal failure.MethodThe expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic acid or in renal tubular epithelial cells (MCT) stressed in culture.ResultsRenal mRNA levels encoding for c-myc and BclxL were elevated in ARF while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. Expression of tumor necrosis factor (TNF-α), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increased in some tubuli and absent in others, while Bcl2 expression decreased diffusely. Bax staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is present in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) and sensitization to TNF-α-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-α increased the mRNA levels encoding for c-myc and decreased BclxL expression. Neither MCT cells nor the kidney expressed BclxS.ConclusionsA relative deficit of survival factors likely contributes to changes in levels of BclxL and Bax in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-α that is increased in ARF and a potential source of increased c-myc, a downstream facilitator of cell death. These findings implicate members of the Bcl2 family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.

The FasL-Fas system regulates renal cell apoptosis, as well as the immune and inflammatory responses. Evidence that FasL and Fas participate in renal injury may be summarized along modified Koch's postulates (Table 1): (i) FasL is expressed by renal cells and during renal injury, (ii) activation of the Fas receptor promotes apoptosis of cultured renal cells, (iii) Fas agonists induce glomerular injury but they may also decrease renal injury by limiting injurious immunological responses, (iv) mice with disrupted FasL/Fas systems are protected from tubular cell injury during ischaemia reperfusion, although they develop autoimmune glomerulonephritis if other genetic predisposing factors are present. FasL/Fas must be considered a new target for therapeutic intervention in renal injury. Therapeutic modulation of Fas should aim not only at protecting intrinsic glomerular or tubular epithelial cells from death, but also at modulating the immune, inflammatory, and fibrogenic responses. Possible therapeutic interventions include Fas agonists, soluble Fas receptors, or other antagonists, and targetting of Fas to undesired cells, such as fibroblasts, in order to decrease their numbers in a physiological manner through apoptosis. Any therapeutic attempt should carefully take into account the possible effects of interference with Fas in other 1833 cell systems. Given the complexities of the FasL/Fas system, further studies are warranted.

Renal fibrosis is characterized by an increased number of fibroblasts and excessive deposition of extracellular matrix. Apoptotic cell death is a physiological mechanism to limit cell numbers, and an insufficient rate of death may contribute to fibroblast accumulation. However, little is known about the regulation of renal fibroblast survival. The authors have studied the interaction of cytokines and the Fas receptor in the regulation of apoptosis of renal fibroblasts and have observed that murine renal fibroblasts express Fas and the Fas ligand. Tumor necrosis factor alpha (TNFalpha) and agonistic anti-Fas antibodies induce apoptosis of renal fibroblasts in a time- and dose-dependent manner. Serum contains survival factors for renal fibroblasts. Both serum deprivation and TNFalpha increase the sensitivity to Fas-induced death and the expression of fas mRNA and Fas receptor. By contrast, insulin-like growth factor-1 decreases apoptosis induced by both serum deprivation and Fas activation and partially prevents the increase in Fas receptor expression induced by serum deprivation. Murine renal fibroblasts express constitutively both fas ligand mRNA and cell-surface Fas ligand, but the authors could not demonstrate a role for Fas ligand in the autocrine regulation of fibroblast survival. These data suggest that Fas and other cytokines cooperate to regulate renal fibroblast apoptosis. Modulation of the Fas death-signaling pathway in renal fibroblasts could represent a new therapeutic target for renal fibrosis.

The retinoblastoma gene product (pRb) controls proliferation and differentiation processes in stratified epithelia. Importantly, and in contrast to other tissues, Rb deficiency does not lead to spontaneous skin tumor formation. As the cyclin-dependent kinase inhibitor p21 regulates proliferation and differentiation in the absence of pRb, we analyzed the consequences of deleting p21 in pRb-ablated stratified epithelia (hereafter pRb(ΔEpi);p21-/-). These mice display an enhancement of the phenotypic abnormalities observed in pRb(ΔEpi) animals, indicating that p21 partially compensates pRb absence. Remarkably, pRb(ΔEpi);p21-/- mice show an acute skin inflammatory phenotype and develop spontaneous epithelial tumors, particularly affecting tongue and oral tissues. Biochemical analyses and transcriptome studies reveal changes affecting multiple pathways, including DNA damage and p53-dependent signaling responses. Comparative metagenomic analyses, together with the histopathological profiles, indicate that these mice constitute a faithful model for human head and neck squamous cell carcinomas. Collectively, our findings demonstrate that p21, in conjunction with pRb, has a central role in regulating multiple epithelial processes and orchestrating specific tumor suppressor functions.

The specific ablation of Rb1 gene in epidermis (Rb(F/F);K14cre) promotes proliferation and altered differentiation but does not produce spontaneous tumour development. These phenotypic changes are associated with increased expression of E2F members and E2F-dependent transcriptional activity. Here, we have focused on the possible dependence on E2F1 gene function. We have generated mice that lack Rb1 in epidermis in an inducible manner (Rb(F/F);K14creER(TM)). These mice are indistinguishable from those lacking pRb in this tissue in a constitutive manner (Rb(F/F);K14cre). In an E2F1-null background (Rb(F/F);K14creER(TM); and E2F1(-/-) mice), the phenotype due to acute Rb1 loss is not ameliorated by E2F1 loss, but rather exacerbated, indicating that pRb functions in epidermis do not rely solely on E2F1. On the other hand, Rb(F/F);K14creER(TM);E2F1(-/-) mice develop spontaneous epidermal tumours of hair follicle origin with high incidence. These tumours, which retain a functional p19(arf)/p53 axis, also show aberrant activation of β-catenin/Wnt pathway. Gene expression studies revealed that these tumours display relevant similarities with specific human tumours. These data demonstrate that the Rb/E2F1 axis exerts essential functions not only in maintaining epidermal homoeostasis, but also in suppressing tumour development in epidermis, and that the disruption of this pathway may induce tumour progression through specific alteration of developmental programs.

Continuous cell renewal in mouse epidermis is at the expense of a pool of pluripotent cells that lie in a well defined niche in the hair follicle known as the bulge. To identify mechanisms controlling hair follicle stem cell homeostasis, we developed a strategy to isolate adult bulge stem cells in mice and to define their transcriptional profile. We observed that a large number of transcripts are underexpressed in hair follicle stem cells when compared to non-stem cells. Importantly, the majority of these downregulated genes are involved in cell cycle. Using bioinformatics tools, we identified the E2F transcription factor family as a potential element involved in the regulation of these transcripts. To determine their functional role, we used engineered mice lacking Rb gene in epidermis, which showed increased expression of most E2F family members and increased E2F transcriptional activity. Experiments designed to analyze epidermal stem cell functionality (i.e.: hair regrowth and wound healing) imply a role of the Rb-E2F axis in the control of stem cell quiescence in epidermis. Electronic supplementary material The online version of this article (doi:10.1007/s12015-010-9139-0) contains supplementary material, which is available to authorized users.

The epidermis is the stratified epithelium that covers and protects the body from external damage. This tissue undergoes continuous cell renewal throughout the life of the individual at the expense of a pool of pluripotent cells, some of them lie in a well defined niche in the hair follicle known as the bulge. Epidermal tumours are the most frequent type of cancer in human populations, as a consequence, the development and progression of these tumours have been extensively characterised and a number of mouse models generated. Over the last years several findings suggest that a subset of cells, named cancer stem cells, could play an important role in tumour development; however, the identity of these cells remains unknown in most cases. Understanding the biology of these cells and their implication in tumour development and progression is crucial to design therapies aimed to target cancer stem cells. In this scenario, the epidermis emerges as a good model to gain deeper insight into the role of adult stem cells in carcinogenesis. Here we summarise recent findings in the field using genetically manipulated mice and how these can be translated to humans.

Programmed cell death is an essential process in the development of the central nervous system (CNS) and is fundamental for the control of the final number of neurons and glial cells. Excessive cell death has been implicated in a growing number of neurodegenerative diseases, such as Alzheimer's, Parkinson's, and multiple sclerosis as well as ischemic injury. We review the contribution of death receptors of the tumor necrosis factor (TNF)/nerve growth factor (NGF) family to cell death and survival in the context of CNS pathology, indicating the possible value of manipulating cell death induced by these receptors for the treatment of CNS diseases and injury.

Squamous cell carcinomas (SCC) represent the most aggressive type of nonmelanoma skin cancer. Although little is known about the causal alterations of SCCs, in organ-transplanted patients the E7 and E6 oncogenes of human papillomavirus, targeting the p53- and pRb-dependent pathways, have been widely involved. Here, we report the functional consequences of the simultaneous elimination of Trp53 and retinoblastoma (Rb) genes in epidermis using Cre-loxP system. Loss of p53, but not pRb, produces spontaneous tumor development, indicating that p53 is the predominant tumor suppressor acting in mouse epidermis. Although the simultaneous inactivation of pRb and p53 does not aggravate the phenotype observed in Rb-deficient epidermis in terms of proliferation and/or differentiation, spontaneous SCC development is severely accelerated in doubly deficient mice. The tumors are aggressive and undifferentiated and display a hair follicle origin. Detailed analysis indicates that the acceleration is mediated by premature activation of the epidermal growth factor receptor/Akt pathway, resulting in increased proliferation in normal and dysplastic hair follicles and augmented tumor angiogenesis. The molecular characteristics of this model provide valuable tools to understand epidermal tumor formation and may ultimately contribute to the development of therapies for the treatment of aggressive squamous cancer. ©2008 American Association for Cancer Research., Oncocycle (CAM), ISCIII-RETIC RD06/0020 (MSC), SAF2005-00033 (MCYT), and Oncology Program from La Caixa Foundation (J.M. Paramio). M. Moral is a recipient of a FIS-BEFI Predoctoral Fellowship from MSC (BF03-00201).

Peritoneal dialysis (PD) and diabetes mellitus share the high glucose concentration in the cell microenvironment. This has led to the suggestion that they may also share pathogenic pathways of cell and tissue injury. Hypotheses have been formulated on the pathogenesis of peritoneal injury in the course of PD that take into account knowledge of the mechanisms of tissue injury in diabetes patients. More recently, research on the pathways of PD complications has uncovered potentially novel mediators of diabetes complications. Accelerated leucocyte apoptosis has been identified as a cause of impaired peritoneal antibacterial defence in PD, which may lead to new therapeutic interventions. In this regard, interference with leucocyte apoptosis by the use of caspase inhibitors may accelerate the clearance of bacteria such as Staphylococcus aureus, which cause significant morbidity in both PD and diabetes patients. Evidence suggests that glucose degradation products in PD solutions accelerate leucocyte apoptosis. In particular, 3,4-di-deoxyglucosone-3-ene (3,4-DGE) accounted for most, if not all, the cytotoxicity of PD fluids against neutrophils and lymphocytes. Interestingly, 3,4-DGE also induces apoptosis in cells, such as renal epithelium, from organs that are targets of diabetes complications. This raises the possibility that apoptosis induction by glucose metabolites that are the key participants in PD complications may underlie the pathogenesis of some features of diabetic tissue injury.

Paracetamol (also known as acetaminophen) causes acute and chronic renal failure. While the mechanisms leading to hepatic injury have been extensively studied, the molecular mechanisms of paracetamol-induced nephrotoxicity are poorly defined. Paracetamol induced cell death with features of apoptosis in murine proximal tubular epithelial cells. While paracetamol increased the expression of the death receptor Fas on the cell surface, the Fas pathway was not involved in the paracetamol-induced apoptosis of tubular cells. The mitochondrial pathway was not activated during paracetamol-induced apoptosis; there was no dissipation of mitochondrial potential or release of apoptogenic factors such as cytochrome c or Smac/DIABLO. However, paracetamol-induced apoptosis is a caspase-dependent process that involves activation of caspase-9 and caspase-3 in the absence of cytosolic cytochrome c or Smac/DIABLO. The authors also detected induction of endoplasmic reticulum (ER) stress, characterized by GADD153 upregulation and translocation to the nucleus, as well as caspase-12 cleavage. Interestingly, after treatment of murine tubular cells with paracetamol and calpain inhibitors, the caspase-12 cleavage product was still detectable, and calpain inhibitors were unable to protect tubular cells from paracetamol-induced apoptosis. The results suggest that induction of apoptosis may underlie the nephrotoxic potential of paracetamol and identify ER stress as a therapeutic target in nephrotoxicity.

Apoptosis is an active form of cell death that, in balance with mitosis, regulates cell number. Cell number abnormalities are a frequent feature of renal disease. We now review current concepts on the molecular regulation of apoptotic cell death, including the influence of survival and lethal factors from the extracellular microenvironment as well as the role of intracellular regulators of apoptosis, such as death receptors, proapoptotic and antiapoptotic bcl2-related proteins, the mitochondria and caspases. In addition the role of apoptosis in the genesis, persistence and progression and remodeling and resolution of renal injury is discussed. Information on the expression and function of apoptosis regulatory proteins in specific renal syndromes is summarized. Finally, future perspectives in research and clinical intervention are discussed.

Agonistic anti-Fas antibodies induce glomerular cell apoptosis in mice in vivo. Recent studies suggest that apoptotic cell death regulates the cell complement in glomerular diseases. However, little is known about the factors that promote glomerular cell apoptosis. Activation of the Fas receptor by the Fas ligand or agonistic antibodies triggers apoptosis in some cell types that express Fas. Cultured human mesangial cell are among the cells that undergo apoptosis upon Fas activation, but it is unclear whether mesangial cells are sensitive to death induced by Fas in vivo. We have now explored the role of Fas in experimental glomerular injury. Murine mesangial cells in culture express fas and undergo apoptosis when stimulated with the Jo2 agonistic anti-Fas mAb. A fas mRNA transcript is present in normal murine kidney and freshly isolated glomeruli. Balb-c mice developed hematuria and proteinuria within 24 hours of the intraperitoneal injection of 10 µg Jo2 anti-Fas mAb. In addition to liver cell apoptosis, glomerular cell apoptosis and mesangial cell depletion were evident in the kidney at three hours and more pronounced at 24 hours. Glomerular and liver injury were not prevented by decomplementation. These data suggest that Fas activation in vivo by specific antibodies induces glomerular and mesangial cell apoptosis in mice.

Tubular cell loss is prominent both in acute and chronic renal failure. Apoptosis and its regulatory mechanisms contribute to cell number regulation in the kidney. The potential role of apoptosis ranges from induction and progression to repair of renal injury. However, therapeutic interest has focused in preventing the apoptotic loss of tubular cells that leads to acute and chronic renal failure. Death ligands and receptors, such as tumor necrosis factor and Fas ligand, proapoptotic and antiapoptotic Bcl2 family members and caspases have all been shown to participate in apoptosis regulation in the course of renal cell injury. Nevertheless, the precise role of these proteins is unclear, and the participation of most known apoptosis regulatory proteins has not been studied. We now review the role of apoptosis in renal injury, the potential molecular targets of therapeutic intervention, the therapeutic weapons to modulate the activity of these targets and the few examples of therapeutic intervention on apoptosis, with emphasis in acute renal failure.

Missense mutations in TP53 gene promote metastasis in human tumours. However, little is known about the complete loss of function of p53 in tumour metastasis. Here we show that squamous cell carcinomas generated by the specific ablation of Trp53 gene in mouse epidermis are highly metastatic. Biochemical and genome-wide mRNA and miRNA analyses demonstrated that metastases are associated with the early induction of epithelial-mesenchymal transition (EMT) and deregulated miRNA expression in primary tumours. Increased expression of miR-21 was observed in undifferentiated, prometastatic mouse tumours and in human tumours characterized by p53 mutations and distant metastasis. The augmented expression of miR-21, mediated by active mTOR and Stat3 signalling, conferred increased invasive properties to mouse keratinocytes in vitro and in vivo, whereas blockade of miR-21 in a metastatic spindle cell line inhibits metastasis development. Collectively these data identify novel molecular mechanisms leading to metastasis in vivo originated by p53 loss in epithelia.