Tenomodulin is necessary for tenocyte proliferation and tendon maturation

Tenomodulin (Tnmd) is a member of a new family of type II transmembrane glycoproteins. It is predominantly expressed in tendons, ligaments, and eyes, whereas the only other family member, chondromodulin I (ChM-I), is highly expressed in cartilage and at lower levels in the eye and thymus. The C-terminal extracellular domains of both proteins were shown to modulate endothelial-cell proliferation and tube formation in vitro and in vivo. We analyzed Tnmd function in vivo and provide evidence that Tnmd is processed in vivo and that the proteolytically cleaved C-terminal domain can be found in tendon extracts. Loss of Tnmd expression in gene targeted mice abated tenocyte proliferation and led to a reduced tenocyte density. The deposited amounts of extracellular matrix proteins, including collagen types I, II, III, and VI and decorin, lumican, aggrecan, and matrilin-2, were not affected, but the calibers of collagen fibrils varied significantly and exhibited increased maximal diameters. Tnmd-deficient mice did not have changes in tendon vessel density, and mice lacking both Tnmd and ChM-I had normal retinal vascularization and neovascularization after oxygen-induced retinopathy. These results suggest that Tnmd is a regulator of tenocyte proliferation and is involved in collagen fibril maturation but do not confirm an in vivo involvement of Tnmd in angiogenesis.     

APOBEC3A can activate the DNA damage response and cause cell-cycle arrest

Human apolipoprotein-B mRNA-editing catalytic polypeptide-like 3 (APOBEC3) proteins constitute a family of cytidine deaminases that mediate restriction of retroviruses, endogenous retro-elements and DNA viruses. It is well established that these enzymes are potent mutators of viral DNA, but it is unclear whether their editing activity is a threat to the integrity of the cellular genome. We show that expression of APOBEC3A can lead to induction of DNA breaks and activation of damage responses in a deaminase-dependent manner. Consistent with these observations, APOBEC3A expression induces cell-cycle arrest. These results indicate that cellular DNA is vulnerable to APOBEC3 activity and deregulated expression of APOBEC3A could threaten genomic integrity.     

Transforming growth factors and the regulation of cell proliferation

The number of different growth regulatory molecules which have been isolated and characterized is continuing to increase. As more information is obtained, it has become apparent that the cooperative actions of many factors with distinct activities is necessary for appropriate proliferative responses. An interplay of both growth stimulatory and growth inhibitory factors is essential for normal growth. Of crucial importance, therefore, is the appropriate regulation of growth factors. Unregulated expression, synthesis, posttranslational processing or activation of either positive or negative growth signals may contribute to neoplastic transformation (Fig. 3). Altered responses to normally positive or negative signals by transformed cells have been demonstrated by several investigators [64, 79, 84]. While altered growth factor responses in transformed cells are well documented, the mechanisms responsible for the loss of growth control are poorly understood and are likely to be both complex and numerous. Continued efforts to dissect and comprehend fully growth factor action on normal cells will be necessary before an understanding of neoplastic transformation can be achieved.     

Mouse epidermal keratinocytes. Clonal proliferation and response to hormones and growth factors in serum-free medium

A serum-free medium (LEP-1) has been developed for mouse epidermal keratinocytes. LEP-1 consists of "Ca2+-free" Eagle's MEM with non-essential amino acids and seven added supplements (transferrin, 5 micrograms/ml; epidermal growth factor (EGF), 5 ng/ml; hydrocortisone, 0.5 microM; insulin, 5 micrograms/ml; phosphoethanolamine and ethanolamine, each 50 microM; bovine pituitary extract, 180 micrograms of protein/ml). Although serum-free the culture system was dependent for growth on bovine pituitary extract as the only still undefined supplement. LEP-1 supports sustained multiplication of mouse keratinocytes for 25 or more population doublings. A clonal growth assay was developed to investigate the action of growth factors, hormones and other supplements on keratinocytes. Cells grown in LEP-1 (calcium concentration was 0.03 mM) maintained a high proliferative rate and presented the typical morphology of basal epidermal cells. When the calcium concentration of the medium was raised to 1.0 mM, the cells were triggered to differentiate terminally. The epithelial nature of the cells was demonstrated both by electron microscopy and by immunostaining with anti-keratin antibody. The maturation stage of the keratinocytes was defined by several morphological features during the proliferative phase and in terminally differentiating cultures. This serum-free system supported a useful number of cell divisions while keratinocytes retained the capacity to undergo terminal differentiation when given the appropriate stimulus. It provides, therefore, provides a useful model for investigations on growth, differentiation and malignant transformation of epidermal cells in culture.     

Mineral and vitamin deficiencies can accelerate the mitochondrial decay of aging

Mitochondrial oxidative decay, which is a major contributor to aging, is accelerated by many common micronutrient deficiencies. One major mechanism is inhibition of the pathway of heme biosynthesis in mitochondria, which causes a deficit of heme-a. Heme-a, only found in Complex IV, is selectively diminished, resulting in oxidant leakage and accelerated mitochondrial decay, which leads to DNA damage, neural decay, and aging. We emphasize those deficiencies, which appear to cause damage through this mechanism, particularly minerals such as iron (25% of menstruating women ingest <50% of the RDA) or zinc (10% of the population ingest <50% of the RDA). Several vitamin deficiencies, such as biotin or pantothenic acid, also increase mitochondrial oxidants through this mechanism. Additionally, other minerals such as magnesium and manganese that play a role in mitochondrial metabolism, but do not affect heme directly, are discussed. An optimum intake of micronutrients could tune up metabolism and give a marked increase in health, particularly for the poor, elderly, and obese, at little cost.     

Hepatitis B virus surface antigen can activate dendritic cells and modulate T helper type immune response

Hepatitis B virus surface antigen (HBsAg) is a major antigen of hepatitis B virus (HBV). Dendritic cells (DC) of HBV carriers have been reported to exhibit functional impairment. In this study, the role of HBsAg on mice bone marrow-derived dendritic cells and immune responses in vivo was studied. The immune modulatory function of HBsAg was explored by using mice bone marrow-derived dendritic cells in vitro and also by examining an ovalbumin (OVA) specific immune response in vivo. Treatment of dendritic cells with HBsAg resulted in enhanced cell surface expression of cluster of differentiation (CD) 80, CD83, CD86, and major histocompatibility complex (MHC) class II, and enhanced production of interleukin (IL)-12 p40 and IL-12 p70. Treatment of dendritic cells with HBsAg resulted in decreased T cell secretion of IL-5 by OVA stimulation. In addition, the results showed stronger OVA-specific immunoglobulin (Ig) M and weaker IgG responses in mice sera when they had been immunized with OVA and co-injected with HBsAg. It was also found that the mice exhibited significant enhancement of anti-OVA IgG2a antibody (Ab), as well as marked inhibition of IgG1 Ab production. In cellular immune responses, IL-5 production was significantly decreased and interferon (IFN)-γ increased in the group co-injected with HBsAg. On the other hand, the induction of lymphoproliferative response to OVA stimulation in spleen cells was decreased in the HBsAg co-injected group. These results demonstrate that HBsAg can affect the differentiation of T helper (Th) cells, which might provide a strategy for improving its prophylactic and therapeutic efficacy.     

Numerous growth factors can influence in vitro megakaryocytopoiesis

At least two classes of human megakaryocyte progenitor cells have been identified: the burst-forming unit megakaryocyte (BFU-MK) and the colony-forming unit megakaryocyte (CFU-MK). The BFU-MK is the most primitive progenitor cell committed to the megakaryocytic lineage. The CFU-MK appears to be a more differentiated megakaryocyte progenitor cell and is thought to be ultimately a descendant of the BFU-MK. A number of recombinant cytokines have recently been shown to be able to promote megakaryocyte colony formation in vitro. Recombinant GM-CSF and IL-3, in particular, have the ability to promote both CFU-MK- and BFU-MK-derived colony stimulatory formation. The activities of these two cytokines on in vitro megakaryocytopoiesis are also additive. Recent results of clinical trials in both primates and humans, in which these glycoproteins were administered in vivo, suggest that these cytokines, both alone and in combination, can enhance in vivo thrombopoiesis and therefore may be potentially useful in the treatment of thrombocytopenic disorders.     

FOXA2 controls the anti-oxidant response in FH-deficient cells

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Parathyroid hormone synergizes with non‐cyclic AMP pathways to activate the cyclic AMP response element

Parathyroid hormone (PTH) activates multiple signaling pathways following binding to the PTH1 receptor in osteoblasts. Previous work revealed a discrepancy between cAMP stimulation and CRE reporter activation of truncated PTH peptides, suggesting that additional signaling pathways contribute to activation of the CRE. Using a CRE‐Luciferase reporter containing multiple copies of the CRE stably transfected into the osteoblastic cell line Saos‐2, we tested the ability of modulators of alternative pathways to activate the CRE or block the PTH‐induced activation of the CRE. Activators of non‐cyclic AMP pathways, that is, EGF (Akt, MAPK, JAK/STAT pathways); thapsigargin (intracellular calcium pathway); phorbol myristate acetate (protein kinase C, PKC pathway) induced minor increases in CRE‐luciferase activity alone but induced dramatic synergistic effects in combination with PTH. The protein kinase A (PKA) inhibitor H‐89 (10 µM) almost completely blocked PTH‐induced activation of the CRE‐reporter. Adenylate cyclase inhibitors SQ 22536 and DDA had profound and time‐dependent biphasic effects on the CRE response. The MAPK inhibitor PD 98059 partially inhibited basal and PTH‐induced CRE activity to the same degree, while the PKC inhibitor bisindolylmaleimide (BIS) had variable effects. The calmodulin kinase II inhibitor KN‐93 had no significant effect on the response to PTH. We conclude that non‐cAMP pathways (EGF pathway, calcium pathway, PKC pathway) converge on, and have synergistic effects on, the response of a CRE reporter to PTH. J. Cell. Biochem. 106: 887–895, 2009. © 2009 Wiley‐Liss, Inc.     

生长素响应因子与植物的生长发育

生长素响应因子(Auxin response factor, ARF)作为一类调控生长素响应基因表达的转录因子, 是生长素研究的重要内容。它可与生长素响应基因启动子区域内的生长素响应元件结合, 促进或抑制基因的表达。文章介绍了植物体内ARF家族的分子生物学近年来的研究进展, 同时也讨论了ARF转录因子的结构、ARF基因的表达调控、ARF在植物生长发育及信号转导中的作用以及ARF对靶基因的调控机制等内容。植物ARF成员都有一定的同源性, 大多含有4个结构域, 在多种组织和器官中都有表达, 其表达受到转录及转录后调控, 并且在介导生长素与其它激素之间相互作用方面扮演重要角色。     

Control of proliferation by myeloid growth factors.

At present the molecular events which regulate the proliferation and developmental fates of haemopoietic cells are poorly understood. Until recently, the only receptor for the myeloid growth factors which had been characterized extensively was that for M-CSF (c-fms). The molecular cloning of receptors for IL-3, GM-CSF and G-CSF should now permit rapid progress in the analysis of receptor-mediated haemopoietic cell differentiation and development, and should also reveal how the process of leukaemic transformation effects these events.