Does prothymosin-alpha act as molecular switch between apoptosis and autophagy?

RAGE (Receptor for Advanced Glycation Endproducts), RAGE ligands, and their role in cancer and inflammation

The Receptor for Advanced Glycation Endproducts [RAGE] is an evolutionarily recent member of the immunoglobulin super-family, encoded in the Class III region of the major histocompatability complex. RAGE is highly expressed only in the lung at readily measurable levels but increases quickly at sites of inflammation, largely on inflammatory and epithelial cells. It is found either as a membrane-bound or soluble protein that is markedly upregulated by stress in epithelial cells, thereby regulating their metabolism and enhancing their central barrier functionality. Activation and upregulation of RAGE by its ligands leads to enhanced survival. Perpetual signaling through RAGE-induced survival pathways in the setting of limited nutrients or oxygenation results in enhanced autophagy, diminished apoptosis, and (with ATP depletion) necrosis. This results in chronic inflammation and in many instances is the setting in which epithelial malignancies arise. RAGE and its isoforms sit in a pivotal role, regulating metabolism, inflammation, and epithelial survival in the setting of stress. Understanding the molecular structure and function of it and its ligands in the setting of inflammation is critically important in understanding the role of this receptor in tumor biology.

Induction of autophagy in malignant rhabdoid tumor cells by the histone deacetylase inhibitor FK228 through AIF translocation

Malignant rhabdoid tumors (MRT) exhibit a very poor prognosis because of their resistance to chemotherapeutic agents and new therapies are needed for the treatment of this cancer. Here, we show that the histone deacetylase (HDAC) inhibitor FK228 (depsipeptide) has an antitumor effect on MRT cells both in vitro and in vivo. FK228 is a unique cyclic peptide and is among the most potent inhibitors of both Class I and Class II HDACs. FK228 inhibited proliferation and induced apoptosis in all MRT cell lines tested. Preincubation with the pancaspase inhibitor zVAD-fmk did not completely rescue FK228-induced cell death, although it did inhibit apoptosis. Transmission electron microscopy (TEM) showed that FK228 could stimulate MRT cells to undergo apoptosis, necrosis or autophagy. FK228 converted unconjugated microtubule-associated protein light chain 3 (LC3-I) to conjugated light chain 3 (LC3-II) and induced localization of LC3 to autophagosomes. Apoptosis inducing factor (AIF), which plays a role in caspase-independent cell death, translocated to the nucleus in response to FK228 treatment. Moreover, small interfering RNA (siRNA) targeting of AIF prevented the morphological changes associated with autophagy and redistribution of LC3 to autophagosomes. Disrupting autophagy with chloroquine treatment enhanced FK228-induced cell death. In vivo, FK228 caused a reduction in tumor size and induced autophagy in tumor tissues. Using immunoelectron microscopy, we confirmed AIF translocation into the nucleus of FK228-induced autophagic cells in vivo. Thus, FK228 is a novel candidate for an antitumor agent for MRT cells.

Apoptosis: a review of programmed cell death

The process of programmed cell death, or apoptosis, is generally characterized by distinct morphological characteristics and energy-dependent biochemical mechanisms. Apoptosis is considered a vital component of various processes including normal cell turnover, proper development and functioning of the immune system, hormone-dependent atrophy, embryonic development and chemical-induced cell death. Inappropriate apoptosis (either too little or too much) is a factor in many human conditions including neurodegenerative diseases, ischemic damage, autoimmune disorders and many types of cancer. The ability to modulate the life or death of a cell is recognized for its immense therapeutic potential. Therefore, research continues to focus on the elucidation and analysis of the cell cycle machinery and signaling pathways that control cell cycle arrest and apoptosis. To that end, the field of apoptosis research has been moving forward at an alarmingly rapid rate. Although many of the key apoptotic proteins have been identified, the molecular mechanisms of action or inaction of these proteins remain to be elucidated. The goal of this review is to provide a general overview of current knowledge on the process of apoptosis including morphology, biochemistry, the role of apoptosis in health and disease, detection methods, as well as a discussion of potential alternative forms of apoptosis.

Identification of N-terminal acetylation of recombinant human prothymosin α in Escherichia coli

Functional modification of protein through N-terminal acetylation is common in eukaryotes but rare in prokaryotes. Prothymosin alpha is an essential protein in immune stimulation and apoptosis regulation. The protein is N-terminal acetylated in eukaryotes, but similar modification has never been found in recombinant protein produced in prokaryotes. In this study, two mass components of recombinant human prothymosin alpha expressed in Escherichia coli were identified and separated by RP-HPLC. Mass spectrometry of the two components showed that one of them had a 42 Da mass increment as compared with the theoretical mass of human prothymosin alpha, which suggested a modification of acetylation. The mass of another one was equal to that of the theoretical one. Peptides mass spectrometry of the modified component showed that the 42-Da mass increment occurred in the N-terminal peptide domain, and MS/MS peptide sequencing of the N-terminal peptide found that the acetylated modification occurred at the N-terminal serine residue. So, part of the recombinant human prothymosin alpha produced by E. coli was N-terminal acetylated. This finding adds a new clue for the mechanism of acetylated modification in prokaryotes, and also suggested a new method for production of N-terminal modificated prothymosin alpha and thymosin alpha1.

Identification of novel genes expressed during rhabdomyosarcoma differentiation using cDNA microarrays

Rhabdomyosarcomas (RMS) are highly aggressive tumors that are thought to arise as a consequence of the regulatory disruption of the growth and differentiation of skeletal muscle progenitor cells. Normal myogenesis is characterized by the expression of the myogenic regulatory factor gene family but, despite their expression in RMS, these tumor cells fail to complete the latter stages of myogenesis. The RMS cell line RD-A was treated with 12-O-tetradecanoylphorbol-13-acetate to induce differentiation and cultured for 10 days. RNA was extracted on days 1, 3, 6, 8 and 10. A human skeletal muscle cDNA microarray was developed and used to analyze the global gene expression of RMS tumors over the time-course of differentiation. As a comparison, the genes identified were subsequently examined during the differentiated primary human skeletal muscle cultures. Prothymosin alpha (PTMA), and translocase of inner mitochondrial membrane 10 (Tim10), two genes not previously implicated in RMS, showed reduced expression during differentiation. Marked differences in the expression of PTMA and Tim10 were observed during the differentiation of human primary skeletal muscle cells. These results identify several new genes with potential roles in the myogenic arrest present in rhabdomyosarcoma. PTMA expression in RMS biopsy samples might prove to be an effective diagnostic marker for this disease.

Role of phosphoinositide 3-kinase in the autophagic death of serum-deprived PC12 cells

The death of serum-deprived undifferentiated PC12 cells shows both autophagic and apoptotic features. Since it is still controversial whether the autophagy is instrumental in the cell death or a mere epiphenomenon, we tested the effects of inhibiting the autophagy by a variety of phosphoinositide 3-kinase inhibitors, and provided evidence that the autophagy, or a related trafficking event, is indeed instrumental in the cell death. Furthermore, by comparing the effects of PI3-K inhibition and caspase-inhibition on autophagic and apoptotic cellular events, we showed that in this case the autophagic and apoptotic mechanisms mediate cell death by parallel pathways and do not act in series.

Nano neodymium oxide induces massive vacuolization and autophagic cell death in non-small cell lung cancer NCI-H460 cells

Neodymium, a rare earth element, was known to exhibit cytotoxic effects and induce apoptosis in certain cancer cells. Here we show that nano-sized neodymium oxide (Nano Nd2O3) induced massive vacuolization and cell death in non-small cell lung cancer NCI-H460 cells at micromolar equivalent concentration range. Cell death elicited by Nano Nd2O3 was not due to apoptosis and caspases were not involved. Electron microscopy and acridine orange staining revealed extensive autophagy in the cytoplasm of the cells treated by Nano Nd2O3. Autophagy induced by Nano Nd2O3 was accompanied by S-phase cell cycle arrest, mild disruption of mitochondrial membrane potential, and inhibition of proteasome activity. Bafilomycin A1, but not 3-MA, induced apoptosis while inhibiting autophagy. Our results revealed a novel biological function for Nano Nd2O3 and may have implications for the therapy of non-small cell lung cancer.

The role of autophagy in cancer development and response to therapy

Autophagy is a process in which subcellular membranes undergo dynamic morphological changes that lead to the degradation of cellular proteins and cytoplasmic organelles. This process is an important cellular response to stress or starvation. Many studies have shed light on the importance of autophagy in cancer, but it is still unclear whether autophagy suppresses tumorigenesis or provides cancer cells with a rescue mechanism under unfavourable conditions. What is the present state of our knowledge about the role of autophagy in cancer development, and in response to therapy? And how can the autophagic process be manipulated to improve anticancer therapeutics?

Multiple cell death programs: Charon's lifts to Hades

Cells use different pathways for active self-destruction as reflected by different morphology: while in apoptosis (or "type I") nuclear fragmentation associated with cytoplasmic condensation but preservation of organelles is predominant, autophagic degradation of cytoplasmic structures preceding nuclear collapse is a characteristic of a second type of programmed cell death (PCD). The diverse morphologies can be attributed--at least to some extent--to distinct biochemical and molecular events (e.g. caspase-dependent and -independent death programs; DAP-kinase activity, Ras-expression). However, apoptosis and autophagic PCD are not mutually exclusive phenomena. Rather, diverse PCD programs emerged during evolution, the conservation of which apparently allows cells a flexible response to environmental changes, either physiological or pathological.

Gastric transcription profile of Helicobacter pylori infection in the rhesus macaque

Infection with Helicobacter pylori is usually asymptomatic but sometimes progresses to peptic ulcer disease or gastric adenocarcinoma. The development of disease involves both host and bacterial factors. In order to better understand host factors in pathogenesis, we studied the gastric transcription profile of H. pylori infection in the rhesus macaque by using DNA microarrays. Significant changes were found in the expression of genes important for innate immunity, chemokines and cytokines, cell growth and differentiation, apoptosis, structural proteins, and signal transduction and transcription factors. This broad transcription profile demonstrated expected up-regulation of cell structural elements and the host inflammatory and immune response, as well as the novel finding of down-regulation of heat shock proteins. These results provide a unique view of acute H. pylori infection in a relevant animal model system and will direct future studies regarding the host response to H. pylori infection.

Autophagy as a cell death and tumor suppressor mechanism

Autophagy is characterized by sequestration of bulk cytoplasm and organelles in double or multimembrane autophagic vesicles, and their delivery to and subsequent degradation by the cell's own lysosomal system. Autophagy has multiple physiological functions in multicellular organisms, including protein degradation and organelle turnover. Genes and proteins that constitute the basic machinery of the autophagic process were first identified in the yeast system and some of their mammalian orthologues have been characterized as well. Increasing lines of evidence indicate that these molecular mechanisms may be recruited by an alternative, caspase-independent form of programmed cell death, named autophagic type II cell death. In some settings, autophagy and apoptosis seem to be interconnected positively or negatively, introducing the concept of 'molecular switches' between them. Additionally, mitochondria may be central organelles integrating the two types of cell death. Malignant transformation is frequently associated with suppression of autophagy. The recent implication of tumor suppressors like Beclin 1, DAP-kinase and PTEN in autophagic pathways indicates a causative role for autophagy deficiencies in cancer formation. Autophagic cell death induction by some anticancer agents underlines the potential utility of its induction as a new cancer treatment modality.