DNA damage-induced translocation of S100A11 into the nucleus regulates cell proliferation

Background  

Proteins are able to react in response to distinct stress stimuli by alteration of their subcellular distribution. The stress-responsive protein S100A11 belongs to the family of multifunctional S100 proteins which have been implicated in several key biological processes. Previously, we have shown that S100A11 is directly involved in DNA repair processes at damaged chromatin in the nucleus. To gain further insight into the underlying mechanism subcellular trafficking of S100A11 in response to DNA damage was analyzed.     

A component of the interphase cytoskeleton is cyclically recruited into spindle poles during mitosis

During the transition from interphase to mitosis, proteins are recruited into forming spindle poles [Leslie, Cell Motil. Cytoskeleton 16:225-228, 1990]. Antibodies which recognize these recruited components clearly label spindle poles during mitosis but the location and character of such proteins during interphase remain a mystery. Competition assays using an antibody to a recruited spindle pole protein show that in its disperse form the spindle pole protein is a highly insoluble component of the cytoskeleton which is dispersed to such an extent during interphase that it is difficult to identify by immunolocalization. The function of recruited spindle pole proteins is unknown but the aggregation/dispersion cycle and the antigen are highly conserved, appearing in sea urchin embryos and tissue culture cells.     

Cyclin E is recruited to the nuclear matrix during differentiation, but is not recruited in cancer cells

Cyclin E supports pre-replication complex (pre-RC) assembly, while cyclin A-associated kinase activates DNA synthesis. We show that cyclin E, but not A, is mounted upon the nuclear matrix in sub-nuclear foci in differentiated vertebrate cells, but not in undifferentiated cells or cancer cells. In murine embryonic stem cells, Xenopus embryos and human urothelial cells, cyclin E is recruited to the nuclear matrix as cells differentiate and this can be manipulated in vitro. This suggests that pre-RC assembly becomes spatially restricted as template usage is defined. Furthermore, failure to become restricted may contribute to the plasticity of cancer cells.     

Centriole is the pivot co-ordinating dynamic signaling for cell proliferation and organization during early development in the vertebrates

Vertebrates have an elaborate and functionally segmented body. It evolves from a single cell by systematic cell proliferation but attains a complex body structure with exquisite precision. This development requires two cellular events: cell cycle and ciliogenesis. For these events, the dynamic molecular signaling is converged at the centriole. The cell cycle helps in cell proliferation and growth of the body and is a highly regulated and integrated process. Its errors cause malignancies and developmental disorders. The cells newly proliferated are organized during organogenesis. For a cellular organization, dedicated signaling hubs are developed in the cells, and most often cilia are utilized. The cilium is generated from one of the centrioles involved in cell proliferation. The developmental signaling pathways hosted in cilia are essential for the elaboration of the body plan. The cilium's compartmental seclusion is ideal for noise-free molecular signaling and is essential for the precision of the body layout. The dysfunctional centrioles and primary cilia distort the development of body layout that manifest as serious developmental disorders. Thus, centriole has a dual role in the growth and cellular organization. It organizes dynamically expressed molecules of cell cycle and ciliogenesis and plays a balancing act to generate new cells and organize them during development. A putative master molecule may regulate and co-ordinate the dynamic gene expression at the centrioles. The convergence of many critical signaling components at the centriole reiterates the idea that centriole is a major molecular workstation involved in elaborating the structural design and complexity in vertebrates.     

Ajuba, a cytosolic LIM protein, shuttles into the nucleus and affects embryonal cell proliferation and fate decisions

Cellular adhesive events affect cell proliferation and differentiation decisions. How cell surface events mediating adhesion transduce signals to the nucleus is not well understood. After cell-cell or cell-substratum contact, cytosolic proteins are recruited to clustered adhesion receptor complexes. One such family of cytosolic proteins found at sites of cell adhesion is the Zyxin family of LIM proteins. Here we demonstrate that the family member Ajuba was recruited to the cell surface of embryonal cells, upon aggregate formation, at sites of cell-cell contact. Ajuba contained a functional nuclear export signal and shuttled into the nucleus. Importantly, accumulation of the LIM domains of Ajuba in the nucleus of P19 embryonal cells resulted in growth inhibition and spontaneous endodermal differentiation. The differentiating effect of Ajuba mapped to the third LIM domain, whereas regulation of proliferation mapped to the first and second LIM domains. Ajuba-induced endodermal differentiation of these cells correlated with the capacity to activate c-Jun kinase and required c-Jun kinase activation. These results suggest that the cytosolic LIM protein Ajuba may provide a new mechanism to transduce signals from sites of cell adhesion to the nucleus, regulating cell growth and differentiation decisions during early development.     

Glutathione is required for growth and prespore cell differentiation in Dictyostelium

Glutathione (GSH) is the most abundant non-protein thiol in eukaryotic cells and acts as reducing equivalent in many cellular processes. We investigated the role of glutathione in Dictyostelium development by disruption of gamma-glutamylcysteine synthetase (GCS), an essential enzyme in glutathione biosynthesis. GCS-null strain showed glutathione auxotrophy and could not grow in medium containing other thiol compounds. The developmental progress of GCS-null strain was determined by GSH concentration contained in preincubated media before development. GCS-null strain preincubated with 0.2 mM GSH was arrested at mound stage or formed bent stalk-like structure during development. GCS-null strain preincubated with more than 0.5 mM GSH formed fruiting body with spores, but spore viability was significantly reduced. In GCS-null strain precultured with 0.2 mM GSH, prestalk-specific gene expression was delayed, while prespore-specific gene and spore-specific gene expressions were not detected. In addition, GCS-null strain precultured with 0.2 mM GSH showed prestalk tendency and extended G1 phase of cell cycle. Since G1 phase cells at starvation differentiate into prestalk cells, developmental defect of GCS-null strain precultured with 0.2 mM GSH may result from altered cell cycle. These results suggest that glutathione itself is essential for growth and differentiation to prespore in Dictyostelium.     

Xrcc3 is recruited to DNA double strand breaks early and independent of Rad51

Rad51-mediated homologous recombination (HR) is essential for maintenance of genome integrity. The Xrcc3 protein functions in HR DNA repair, and studies suggest it has multiple roles at different stages in this pathway. Defects in vertebrate XRCC3 result in elevated levels of spontaneous and DNA damage-induced chromosomal abnormalities, as well as increased sensitivity to DNA damaging agents. Formation of DNA damaged-induced nuclear Rad51 foci requires Xrcc3 and the other Rad51 paralog proteins (Rad51B, Rad51C, Rad51D, Xrcc2), thus supporting a model in which an early function of Xrcc3 involves promoting assembly of active Rad51 repair complexes. However, it is not known whether Xrcc3 or other Rad51 paralog proteins accumulate at DNA breaks, and if they do whether their stable association with breaks requires Rad51. Here we report for the first time that Xrcc3 forms distinct foci in human cells and that nuclear Xrcc3 begins to localize at sites of DNA damage within 10 min after radiation treatment. RNAi-mediated knock down of Rad51 has no effect on the DNA damage-induced localization of Xrcc3 to DNA breaks. Our data are consistent with a model in which Xrcc3 associates directly with DNA breaks independent of Rad51, and subsequently facilitates formation of the Rad51 nucleoprotein filament.     

Incorporation of mammalian actin into microfilaments in plant cell nucleus

Background  

Actin is an ancient molecule that shows more than 90% amino acid homology between mammalian and plant actins. The regions of the actin molecule that are involved in F-actin assembly are largely conserved, and it is likely that mammalian actin is able to incorporate into microfilaments in plant cells but there is no experimental evidence until now.     

Inositol phospho-oligosaccharide stimulates cell proliferation in the early developing inner ear

The ability of an inositol phospho-oligosaccharide (POS) to mimic the mitogenic effects of nerve growth factor (NGF) and insulin on the early development of the inner ear was investigated. POS (10 microM) stimulated the incorporation of [3H]thymidine into the cochleovestibular ganglion by 3.9-fold. NGF (50 ng/ml) stimulation was 4.7-fold. POS and NGF showed no additivity. Cells induced to proliferate by POS overlapped with those expressing NGF receptors. POS, like insulin, potentiated the mitogenic effect of bombesin on the otic vesicle epithelium. DNA synthesis in the presence of bombesin (100 nM) plus POS (10 microM) was increased by 6.4-fold. POS stimulation was not additive with insulin. The results suggest that POS may play a role in growth factor regulation of cell proliferation during embryonic development.     

Expanding insights into the role of cell proliferation in plant development

Development in plants relies largely on the activity of meristems, which are regions at the apices of shoots and roots that are capable of prolonged organogenesis. Developmental patterning and morphogenesis in plants is principally determined by post-embryonic regulation of the shoot, root and flower meristems, which enable plants to modify their form rapidly in response to different environmental conditions. Because meristems are continually generating new organs and tissues, they provide excellent model systems in which to study the processes of cell division, differentiation and organ formation. Here, we describe recent studies and several classic experiments that are helping to uncover the mechanisms controlling meristem development and the role of cell division in morphogenesis and patterning in plants.     

Glutathione stimulates A549 cell proliferation in glutamine-deficient culture: The effect of glutamate supplementation

Extracellular glutathione (GSH) is degraded by an external cell-surface enzyme, γ-glutamyltranspeptidase (γ-GT). The products are transported into cells to participate in important cellular processes. In the present study, we tested the hypothesis that extracellular GSH is a source of glutamic acid for cells that express γ-GT. Under a glutamine-deficient culture condition, the extracellular GSH-supplemented glutamic acid would enhance intracellular glutamine synthesis, thereby stimulating cell proliferation. Human lung carcinoma A549 cells were cultured in glutamine-deficient Dulbecco's modified Eagle medium, and they did not proliferate unless glutamine was supplemented. Extracellular GSH, however, provoked a partial proliferation. The GSH effect correlated with a high level of γ-GT activity and an increased intracellular level of glutamic acid. A constituent amino acid of GSH, glutamic acid but not cysteine, produced the same growth-stimulatory effect as GSH. Furthermore, neither oxothiazolidine-4-carboxylate (OTC), a celluar cysteine-delivery compound, nor cysteinylglycine, a dipeptide released from the γ-GT reaction, stimulated cell proliferation. Moreover, buthionine sulfoximine (BSO), a selective inhibitor of γ-glutamylcysteine synthetase, enhanced the GSH growth stimulatory effect, suggesting that increased cellular GSH synthesis does not correlate with cell growth stimulation. The results obtained demonstrated that glutamine is required for A549 cell proliferation and exogenous GSH partially substitutes for the growth stimulatory action of glutamine. It also suggests that the glutamic acid rather than the cysteine released from the GSH is responsible for the cell proliferation. © 1994 Wiley-Liss, Inc.