AU-Rich Elements in the Collagenase 3 mRNA Mediate Stabilization of the Transcript by Cortisol in Osteoblasts

Uncovering early thyroid hormone signalling events through temperature-mediated activation of molecular memory in the cultured bullfrog tadpole tail fin

Thyroid hormone (TH) is a critical signalling molecule for all vertebrate organisms, playing a crucial role in postembryonic development. The best-studied mechanism of TH response is through modulating gene expression, however TH's involvement in coordinating the early steps in the TH signal transduction pathway is still poorly understood. The American bullfrog, Rana [Lithobates] catesbeiana, is a useful model to study these early responses as tadpole post-embryonic development in the form of metamorphosis of the tadpole into a frog can be experimentally induced by TH exposure. The rate of TH-induced metamorphosis can be modulated by temperature where sufficiently cold temperatures (5 °C) completely halt precocious metamorphosis. Interestingly, when premetamorphic tadpoles exposed to exogenous THs at 5 °C are shifted to permissive temperatures (24 °C), their metamorphic rate exceeds that of TH-exposed tadpoles at the permissive temperature. This suggests that a molecular memory of TH exposure is retained at 5 °C even after THs are cleared at this low temperature. However, the molecular memory machinery is poorly understood. Herein we use RNA-seq analysis to identify potential components of the molecular memory in cultured tail fin that allows for the recapitulation of the molecular memory phenomenon. Eighty-one gene transcripts were TH-responsive at 5 °C compared to matched controls indicating that the molecular memory is more complex than previously thought. Many of these transcripts encode transcription factors including thyroid hormone-induced B/Zip, thibz, and a novel krüppel-like factor family member, klfX. Actinomycin D and cycloheximide treatment had no effect on their TH induction suggesting that a change in transcription or translation is not required. Rather a change in RNA stability may be a possible mechanism contributing to the molecular memory. The ability to manipulate temperature and TH response in cultured organs provide an exciting opportunity to further elucidate the early TH signalling mechanisms during postembryonic development.

The collagenases: are they tractable targets for preventing cartilage destruction in osteoarthritis?

INTRODUCTION

The etiology and pathogenesis of osteoarthritis (OA) have been intensely investigated; however, the disease course and progression are not completely understood. A prominent role for interstitial collagenases is recognized in this degenerative process, hence strategies to target them are of major interest.

AREAS COVERED

The pathogenesis of OA, the role of interstitial collagenases (MMP-1, -8 and -13) and collagenase modifying drugs are examined and discussed. We reviewed relevant papers from PubMed and Google Scholar.

EXPERT OPINION

There is strong evidence for the therapeutic potential of MMP inhibitors in OA; however, they are not expected to impact the inflammatory process. Therefore, there is a need for a relative inhibitor of MMP-13 collagenase which possesses anti-inflammatory properties. The identification of novel broad-spectrum relative multiple peptidase inhibitors could provide desirable tools for the prophylaxis, cure, or treatment of diseases involving articular cartilage (AC) degradation, in particular OA.

Glucocorticoids inhibit notch target gene expression in osteoblasts

Glucocorticoids in excess suppress osteoblast function and cause osteoporosis. We demonstrated that cortisol induces the expression of selected Notch receptors in osteoblasts, revealing a potential mechanism for the skeletal effects of glucocorticoids. However, it remains to be determined whether increased expression of Notch receptors results into enhanced signaling. Following activation of Notch, its intracellular domain (NICD) binds to the DNA-associated protein recombination signal binding protein for immunoglobulin kappa-J region (RBPJ) and induces the expression of target genes such as Hey1, Hey2, and HeyL. To determine whether glucocorticoids modulate Notch signaling in the skeleton, 1 month old wild-type mice were administered prednisolone or placebo and sacrificed after 72 h, and gene expression was analyzed in femoral bone. Prednisolone induced Tsc22d3, a glucocorticoid target gene, and suppressed Hey1 and HeyL expression, which is indicative of inhibited Notch receptor activity or direct Hey downregulation. To determine the mechanisms of Hey suppression, wild-type osteoblast-enriched cells were seeded on the Notch cognate ligand Delta-like (DLL)1 or transfected with constructs expressing the NOTCH1 NICD fragment and exposed to either cortisol or vehicle. Cortisol opposed the induction of mRNA and heterogeneous nuclear RNA for Hey1, Hey2, and HeyL by DLL1, but had no effect on mRNA stability, indicating that glucocorticoids inhibit Hey expression by transcriptional mechanisms. Transactivation studies and electrophoretic mobility shift assays revealed that cortisol did not oppose RBPJ-mediated transcription or RBPJ/DNA interactions, respectively. In conclusion, glucocorticoids suppress expression of Hey1, Hey2, and HeyL in osteoblasts by RBPJ-independent transcriptional mechanisms.

New insights on the MMP-13 regulatory network in the pathogenesis of early osteoarthritis

Osteoarthritis (OA) is the most common joint disorder and affects approximately half of the aged population. Current treatments for OA are largely palliative until the articular cartilage has been deeply damaged and irreversible morphological changes appear. Thus, effective methods are needed for diagnosing and monitoring the progression of OA during its early stages when therapeutic drugs or biological agents are most likely to be effective. Various proteinases involved in articular cartilage degeneration in pre-OA conditions, which may represent the earliest reversible measurable changes, are considered diagnostic and therapeutic targets for early OA. Of these proteinases, matrix metalloproteinase 13 (MMP-13) has received the most attention, because it is a central node in the cartilage degradation network. In this review, we highlight the main MMP-13-related changes in OA chondrocytes, including alterations in the activity and expression level of MMP-13 by upstream regulatory factors, DNA methylation, various non-coding RNAs (ncRNAs), and autophagy. Because MMP-13 and its regulatory networks are suitable targets for the development of effective early treatment strategies for OA, we discuss the specific targets of MMP-13, including upstream regulatory proteins, DNA methylation, non-coding RNAs, and autophagy-related proteins of MMP-13, and their therapeutic potential to inhibit the development of OA. Moreover, the various entities mentioned in this review might be useful as early biomarkers and for personalized approaches to disease prevention and treatment by improving the phenotyping of early OA patients.

MMP-13 is constitutively produced in human chondrocytes and co-endocytosed with ADAMTS-5 and TIMP-3 by the endocytic receptor LRP1

Matrix metalloproteinase 13 (MMP-13) degrades collagenous extracellular matrix and its aberrant activity associates with diseases such as arthritis, cancer, atherosclerosis and fibrosis. The wide range of MMP-13 proteolytic capacity suggests that it is a powerful, potentially destructive proteinase and thus it has been believed that MMP-13 is not produced in most adult human tissues in the steady state. Present study has revealed that human chondrocytes isolated from healthy adults constitutively express and secrete MMP-13, but that it is rapidly endocytosed and degraded by chondrocytes. Both pro- and activated MMP-13 bind to clusters II and III of low-density lipoprotein (LDL) receptor-related protein 1 (LRP1). Domain deletion studies indicated that the hemopexin domain is responsible for this interaction. Binding competition between MMP-13 and ADAMTS-4, -5 or TIMP-3, which also bind to cluster II, further shown that the MMP-13 binding site within cluster II is different from those of ADAMTS-4, -5 or TIMP-3. MMP-13 is therefore co-endocytosed with ADAMTS-5 and TIMP-3 by human chondrocytes. These findings indicate that MMP-13 may play a role on physiological turnover of cartilage extracellular matrix and that LRP1 is a key modulator of extracellular levels of MMP-13 and its internalization is independent of the levels of ADAMTS-4, -5 and TIMP-3.

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ProMMP-13 is constitutively produced and endocytosed by chondrocytes.

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LRP1 is a key modulator of extracellular levels of proMMP-13 and MMP-13.

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ProMMP-13 and MMP-13 directly bind to LRP1 via the hemopexin domain.

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Unique sites on LRP1 for MMP-13 binding have been mapped.

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Co-endocytosis of proMMP-13 with ADAMTS-4, -5 and TIMP-3.

Far upstream element-binding protein 1 is a prognostic biomarker and promotes nasopharyngeal carcinoma progression

Nasopharyngeal carcinoma (NPC) is a malignant epithelial tumor with tremendous invasion and metastasis capacities, and it has a high incidence in southeast Asia and southern China. Previous studies identified that far upstream element-binding protein 1 (FBP1), a transcriptional regulator of c-Myc that is one of the most frequently aberrantly expressed oncogenes in various human cancers, including NPC, is an important biomarker for many cancers. Our study aimed to investigate the expression and function of FBP1 in human NPC. Quantitative real-time RT-PCR (qRT-PCR), western blot and immunohistochemical staining (IHC) were performed in NPC cells and biopsies. Furthermore, the effect of FBP1 knockdown on cell proliferation, colony formation, side population tests and tumorigenesis in nude mice were measured by MTT, clonogenicity analysis, flow cytometry and a xenograft model, respectively. The results showed that the mRNA and protein levels of FBP1, which are positively correlated with c-Myc expression, were substantially higher in NPC than that in nasopharyngeal epithelial cells. IHC revealed that the patients with high FBP1 expression had a significantly poorer prognosis compared with the patients with low expression (P=0.020). In univariate analysis, high FBP1 and c-Myc expression predicted poorer overall survival (OS) and poorer progression-free survival. Multivariate analysis indicated that high FBP1 and c-Myc expression were independent prognostic markers. Knockdown of FBP1 reduced cell proliferation, clonogenicity and the ratio of side populations, as well as tumorigenesis in nude mice. These data indicate that FBP1 expression, which is closely correlated with c-Myc expression, is an independent prognostic factor and promotes NPC progression. Our results suggest that FBP1 can not only serve as a useful prognostic biomarker for NPC but also as a potential therapeutic target for NPC patients.

A glimpse of matrix metalloproteinases in diabetic nephropathy

Matrix metalloproteinases (MMPs) are proteolytic enzymes belonging to the family of zinc-dependent endopeptidases that are capable of degrading almost all the proteinaceous components of the extracellular matrix (ECM). It is known that MMPs play a role in a number of renal diseases, such as, various forms of glomerulonephritis and tubular diseases, including some of the inherited kidney diseases. In this regard, ECM accumulation is considered to be a hallmark morphologic finding of diabetic nephropathy, which not only is related to the excessive synthesis of matrix proteins, but also to their decreased degradation by the MMPs. In recent years, increasing evidence suggest that there is a good correlation between the activity or expression of MMPs and progression of renal disease in patients with diabetic nephropathy and in various experimental animal models. In such a diabetic milieu, the expression of MMPs is modulated by high glucose, advanced glycation end products (AGEs), TGF-β, reactive oxygen species (ROS), transcription factors and some of the microRNAs. In this review, we focused on the structure and functions of MMPs, and their role in the pathogenesis of diabetic nephropathy.

Connective tissue growth factor is a target of notch signaling in cells of the osteoblastic lineage

Connective tissue growth factor (Ctgf) or CCN2 is a protein synthesized by osteoblasts necessary for skeletal homeostasis, although its overexpression inhibits osteogenic signals and bone formation. Ctgf is induced by bone morphogenetic proteins, transforming growth factor β and Wnt; and in the present studies, we explored whether Notch regulated Ctgf expression in osteoblasts. We employed Rosa(Notch) mice, where the Notch intracellular domain (NICD) is expressed following the excision of a STOP cassette, placed between the Rosa26 promoter and NICD. Notch was activated by transduction of adenoviral vectors expressing Cre recombinase (Ad-CMV-Cre). Notch induced Ctgf mRNA levels in a time dependent manner and increased Ctgf heterogeneous nuclear RNA. Notch also destabilized Ctgf mRNA shortening its half-life from 13h to 3h. The effect of Notch on Ctgf expression was lost following Rbpjκ downregulation, demonstrating that it was mediated by Notch canonical signaling. However, downregulation of the classic Notch target genes Hes1, Hey1 and Hey2 did not modify the effect of Notch on Ctgf expression. Wild type osteoblasts exposed to immobilized Delta-like 1 displayed enhanced Notch signaling and increased Ctgf expression. In addition to the effects of Notch in vitro, Notch induced Ctgf in vivo, and calvariae and femurs from Rosa(Notch) mice mated with transgenics expressing the Cre recombinase in cells of the osteoblastic lineage exhibited increased expression of Ctgf. In conclusion, Ctgf is a target of Notch canonical signaling in osteoblasts, and may act in concert with Notch to regulate skeletal homeostasis.

MicroRNA-322 (miR-322) and its target protein Tob2 modulate Osterix (Osx) mRNA stability

Osteogenesis depends on a coordinated network of signals and transcription factors such as Runx2 and Osterix. Recent evidence indicates that microRNAs (miRNAs) act as important post-transcriptional regulators in a large number of processes, including osteoblast differentiation. In this study, we performed miRNA expression profiling and identified miR-322, a BMP-2-down-regulated miRNA, as a regulator of osteoblast differentiation. We report miR-322 gain- and loss-of-function experiments in C2C12 and MC3T3-E1 cells and primary cultures of murine bone marrow-derived mesenchymal stem cells. We demonstrate that overexpression of miR-322 enhances BMP-2 response, increasing the expression of Osx and other osteogenic genes. Furthermore, we identify Tob2 as a target of miR-322, and we characterize the specific Tob2 3'-UTR sequence bound by miR-322 by reporter assays. We demonstrate that Tob2 is a negative regulator of osteogenesis that binds and mediates degradation of Osx mRNA. Our results demonstrate a new molecular mechanism controlling osteogenesis through the specific miR-322/Tob2 regulation of specific target mRNAs. This regulatory circuit provides a clear example of a complex miRNA-transcription factor network for fine-tuning the osteoblast differentiation program.

Identification of prohibitin as a Chikungunya virus receptor protein

Chikungunya virus (CHIKV) has recently re-emerged causing millions of infections in countries around the Indian Ocean. While CHIKV has a broad host cell range and productively infects a number of different cell types, macrophages have been identified as a potential viral reservoir serving to increase the duration of symptoms. To date no CHIKV interacting protein has been characterized and this study sought to identify CHIKV binding proteins expressed on target cell membranes. Two-dimensional virus overlay identified prohibitin (PHB) as a microglial cell expressed CHIKV binding protein. Co-localization, co-immunoprecipitation as well as antibody and siRNA mediated infection inhibition studies all confirmed a role for PHB in mediating internalization of CHIKV into microglial cells. PHB is the first identified CHIKV receptor protein, and this study is evidence that PHB may play a role in the internalization of multiple viruses.

Prostaglandin E2 promotes liver cancer cell growth by the upregulation of FUSE-binding protein 1 expression

Liver cancer is a common human cancer with a high mortality rate and currently there is no effective chemoprevention or systematic treatment. Recent evidence suggests that prostaglandin E(2) (PGE(2)) plays an important role in the occurrence and development of liver cancer. However, the mechanisms through which PGE(2) promotes liver cancer cell growth are not yet fully understood. It has been reported that the increased expression of FUSE-binding protein 1 (FBP1) significantly induces the proliferation of liver cancer cells. In this study, we report that PGE(2) promotes liver cancer cell growth by the upregulation of FBP1 protein expression. Treatment with PGE2 and the E prostanoid 3 (EP3) receptor agonist, sulprostone, resulted in the time-dependent increase in FBP1 protein expression; sulprostone increased the viability of the liver cancer cells. The protein kinase A (PKA) inhibitor, H89, and the adenylate cyclase (AC) inhibitor, SQ22536, inhibited the cell viability accelerated by sulprostone. By contrast, the Gi subunit inhibitor, pertussis toxin (PTX), exhibited no significant effect. Treatment with PGE(2) and sulprostone caused a decrease in JTV1 protein expression, blocked the binding of JTV1 with FBP1, which served as a mechanism for FBP1 degradation, leading to the decreased ubiquitination of FBP1 and the increase in FBP1 protein expression. Furthermore, H89 and SQ22536 prevented the above effects of JTV1 and FBP1 induced by PGE(2) and sulprostone. These findings indicate that the EP3 receptor activated by PGE(2) may couple to Gs protein and activate cyclic AMP (cAMP)-PKA, downregulating the levels of JTV1 protein, consequently inhibiting the ubiquitination of FBP1 and increasing FBP1 protein expression, thus promoting liver cancer cell growth. These observations provide new insights into the mechanisms through which PGE(2) promotes cancer cell growth.

Nuclear factor of activated T-cells (NFAT)C2 inhibits Notch receptor signaling in osteoblasts

Notch receptors regulate osteoblastogenesis, and Notch activation induces cleavage and nuclear translocation of the Notch intracellular domain (NICD), which associates with Epstein-Barr virus latency C-promoter binding factor-1/suppressor of hairless/lag-1 (CSL) and induces transcription of Notch target genes, such as hairy enhancer of split-related with YRPW motif (Hey)1 and Hey2. Nuclear factors of activated T-cells (NFAT) are transcription factors that regulate osteoclastogenesis, but their function in osteoblasts is not clear. Notch inhibits NFATc1 transcription, but interactions between Notch and NFAT are understood poorly. To determine the regulation of NFAT expression by Notch, osteoblasts from Rosa(Notch) mice, where NICD is transcribed following excision of a loxP flanked STOP cassette, were used. Alternatively, wild-type C57BL/6 osteoblasts were exposed to the Notch ligand Delta-like (Dll)1 to induce Notch signaling or to bovine serum albumin as control. In Rosa(Notch) osteoblasts, Notch suppressed NFATc1 expression, increased Nfatc2 mRNA by post-transcriptional mechanisms, and had no effect on NFATc3 and NFATc4 transcripts. Induction of Nfatc2 transcripts by Notch was confirmed in C57BL/6 osteoblasts exposed to Dll1. To investigate NFATc2 function in osteoblasts, constitutively active NFATc2 was overexpressed in Rosa(Notch) osteoblasts. NFATc2 suppressed Notch transactivation and expression of Hey genes. Electrophoretic mobility shift assays revealed that NFATc2 and CSL bind to similar DNA sequences, and chromatin immunoprecipitation indicated that NFATc2 displaced CSL from the Hey2 promoter. The effects of NICD and NFATc2 in Rosa(Notch) osteoblasts were assessed, and both proteins inhibited osteoblast function. In conclusion, Notch stabilizes Nfatc2 transcripts, NFATc2 suppresses Notch signaling, and both proteins inhibit osteoblast function.

Aroclor 1254 disrupts liver glycogen metabolism and enhances acute stressor-mediated glycogenolysis in rainbow trout

The objective of this study was to investigate the impact of short-term exposure to polychlorinated biphenyls on the acute stress response in rainbow trout. Fish were exposed to dietary Aroclor1254 (10mg kg(-1) body mass/day) for 3 days and then subjected to a 3-min handling disturbance and sampled over a 24h recovery after the stressor exposure. In the pre-stress fish, PCB exposure significantly elevated aryl hydrocarbon receptor (AhR) and cytochrome P4501A1 (Cyp1A1) mRNA abundance and Cyp1A protein expression confirming AhR activation. There was no significant effect of PCB on plasma cortisol and glucose levels, while plasma lactate levels were significantly elevated compared to the sham group. PCB exposure significantly elevated liver glycogen content and hexokinase activity, whereas lactate dehydrogenase activity was depressed. Short-term PCB exposure did not modify the acute stressor-induced plasma cortisol, glucose and lactate responses. Liver glycogen content dropped significantly after stressor exposure in the PCB group but not in the sham group. This was matched by a significantly higher liver LDH activity and a lower HK activity during recovery in the PCB group suggesting enhanced glycolytic capacity to fuel hepatic metabolism. Liver AhR, but not Cyp1A1, transcript levels were significantly reduced during recovery from handling stressor in the Aroclor fed fish. Collectively, this study demonstrates that short-term PCB exposure may impair the liver metabolic performance that is critical to cope with the enhanced energy demand associated with additional stressor exposure in rainbow trout.

Nephroblastoma overexpressed (Nov) induces gremlin in ST-2 stromal cell lines by post-transcriptional mechanisms

Nephroblastoma overexpressed (Nov) inhibits osteoblastogenesis in part because it binds bone morphogenetic protein (BMP)-2. In the present study, we investigated whether Nov regulated the expression of the BMP antagonist gremlin. Overexpression of Nov increased gremlin mRNA levels in ST-2 cells, and its downregulation by RNA interference decreased gremlin mRNA. Nov did not affect Grem1 transcription, but prolonged the half-life of gremlin mRNA in ST-2 cells, demonstrating that Nov acts by post-transcriptional mechanisms. This was confirmed by demonstrating that downregulation of Nov destabilizes gremlin transcripts. To assess whether the 3'-untranslated region (UTR) of gremlin mRNA mediated the effect of Nov, the decay of a chimeric cfos gremlin 3'-UTR construct was compared to that of cfos in ST-2 cells. The presence of the gremlin 3'-UTR prolonged the half-life of cfos and was responsible for the effect of Nov. To examine the binding of the gremlin 3'-UTR to ribonucleoproteins, radiolabeled gremlin RNA fragments were incubated with cytosolic extracts from Nov overexpressing and control cells. RNA electrophoretic mobility analysis revealed that Nov enhanced the binding of cytosolic proteins to the fragments spanning the 3'-UTR of gremlin between bases 1,358-1,557 and 1,158-1,357 from the transcriptional start. Mutations of AU-rich elements in these two RNA fragments prevented the formation of RNA-protein complexes induced by Nov. Nov did not alter the binding of cytosolic extracts to sequences present in the 5'-UTR or coding region of gremlin. In conclusion, Nov stabilizes gremlin transcripts, and this effect is possibly mediated by AU-rich elements present in the 3'-UTR of gremlin.

Redox-control of matrix metalloproteinase-1: a critical link between free radicals, matrix remodeling and degenerative disease

Many degenerative disease processes associated with aging result from enhanced extracellular matrix (ECM) breakdown. Concomitant with aberrant matrix destruction are alterations in levels of reactive oxygen species (ROS) generating and detoxification systems. ROS function as second messengers due to their ability to react with wide range of biomolecules resulting in modification of an array of signaling networks. ROS can activate upstream kinases (MKK) responsible for MAPK activation and restrict the activity of their inhibitory phosphatases. Here we focus on the redox-sensitive signaling components that control the expression of MMP-1, which is largely responsible for maintaining ECM homeostasis. Numerous disease processes are associated with shifts in steady state ROS levels that influence overall ECM degradation. This review highlights the redox-sensitive regulatory signals that control the expression of the primary initiating protease MMP-1 and provides strong rational for the use of antioxidant based therapies for treatment of degenerative disorders associated with aberrant matrix destruction.

Overexpression of far upstream element binding proteins: a mechanism regulating proliferation and migration in liver cancer cells

Microtubule-dependent effects are partly regulated by factors that coordinate polymer dynamics such as the microtubule-destabilizing protein stathmin (oncoprotein 18). In cancer cells, increased microtubule turnover affects cell morphology and cellular processes that rely on microtubule dynamics such as mitosis and migration. However, the molecular mechanisms deregulating modifiers of microtubule activity in human hepatocarcinogenesis are poorly understood. Based on profiling data of human hepatocellular carcinoma (HCC), we identified far upstream element binding proteins (FBPs) as significantly coregulated with stathmin. Coordinated overexpression of two FBP family members (FBP-1 and FBP-2) in >70% of all analyzed human HCCs significantly correlated with poor patient survival. In vitro, FBP-1 predominantly induced tumor cell proliferation, while FBP-2 primarily supported migration in different HCC cell lines. Surprisingly, reduction of FBP-2 levels was associated with elevated FBP-1 expression, suggesting a regulatory interplay of FBP family members that functionally discriminate between cell division and mobility. Expression of FBP-1 correlated with stathmin expression in HCC tissues and inhibition of FBP-1 but not of FBP-2 drastically reduced stathmin at the transcript and protein levels. In contrast, further overexpression of FBP-1 did not affect stathmin bioavailability. Accordingly, analyzing nuclear and cytoplasmic areas of HCC cells revealed that reduced FBP-1 levels affected cell morphology and were associated with a less malignant phenotype.

CONCLUSION

The coordinated activation of FBP-1 and FBP-2 represents a novel and frequent pro-tumorigenic mechanism promoting proliferation (tumor growth) and motility (dissemination) of human liver cancer cells. FBPs promote tumor-relevant functions by at least partly employing the microtubule-destabilizing factor stathmin and represent a new potential target structure for HCC treatment.

Growth hormone, insulin-like growth factors, and the skeleton

GH and IGF-I are important regulators of bone homeostasis and are central to the achievement of normal longitudinal bone growth and bone mass. Although GH may act directly on skeletal cells, most of its effects are mediated by IGF-I, which is present in the systemic circulation and is synthesized by peripheral tissues. The availability of IGF-I is regulated by IGF binding proteins. IGF-I enhances the differentiated function of the osteoblast and bone formation. Adult GH deficiency causes low bone turnover osteoporosis with high risk of vertebral and nonvertebral fractures, and the low bone mass can be partially reversed by GH replacement. Acromegaly is characterized by high bone turnover, which can lead to bone loss and vertebral fractures, particularly in patients with coexistent hypogonadism. GH and IGF-I secretion are decreased in aging individuals, and abnormalities in the GH/IGF-I axis play a role in the pathogenesis of the osteoporosis of anorexia nervosa and after glucocorticoid exposure.

Glucocorticoid regulation of human pulmonary surfactant protein-B mRNA stability involves the 3'-untranslated region

Expression of pulmonary surfactant, a complex mixture of lipids and proteins that acts to reduce alveolar surface tension, is developmentally regulated and restricted to lung alveolar type II cells. The hydrophobic protein surfactant protein-B (SP-B) is essential in surfactant function, and insufficient levels of SP-B result in severe respiratory dysfunction. Glucocorticoids accelerate fetal lung maturity and surfactant synthesis both experimentally and clinically. Glucocorticoids act transcriptionally and post-transcriptionally to increase steady-state levels of human SP-B mRNA; however, the mechanism(s) by which glucocorticoids act post-transcriptionally is unknown. We hypothesized that glucocorticoids act post-transcriptionally to increase SP-B mRNA stability via sequence-specific mRNA-protein interactions. We found that glucocorticoids increase SP-B mRNA stability in isolated human type II cells and in nonpulmonary cells, but do not alter mouse SP-B mRNA stability in a mouse type II cell line. Deletion analysis of an artificially-expressed SP-B mRNA indicates that the SP-B mRNA 3'-untranslated region (UTR) is necessary for stabilization, and the region involved can be restricted to a 126-nucleotide-long region near the SP-B coding sequence. RNA electrophoretic mobility shift assays indicate that cytosolic proteins bind to this region in the absence or presence of glucocorticoids. The formation of mRNA:protein complexes is not seen in other regions of the SP-B mRNA 3'-UTR. These results indicate that a specific 126-nucleotide region of human SP-B 3'-UTR is necessary for increased SP-B mRNA stability by glucocorticoids by a mechanism that is not lung cell specific and may involve mRNA-protein interactions.

Functional analysis of KSRP interaction with the AU-rich element of interleukin-8 and identification of inflammatory mRNA targets

mRNA stability is a major determinant of inflammatory gene expression. Rapid degradation of interleukin-8 (IL-8) mRNA is imposed by a bipartite AU-rich element (ARE) in the 3' untranslated region (R. Winzen et al., Mol. Cell. Biol. 24:4835-4847, 2004). Small interfering RNA-mediated knockdown of the ARE-binding protein KSRP resulted in stabilization of IL-8 mRNA or of a beta-globin reporter mRNA containing the IL-8 ARE. Rapid deadenylation was impaired, indicating a crucial role for KSRP in this step of mRNA degradation. The two IL-8 ARE domains both contribute to interaction with KSRP, corresponding to the importance of both domains for rapid degradation. Exposure to the inflammatory cytokine IL-1 has been shown to stabilize IL-8 mRNA through p38 mitogen-activated protein (MAP) kinase and MK2. IL-1 treatment impaired the interaction of KSRP with the IL-8 ARE in a manner dependent on p38 MAP kinase but apparently independent of MK2. Instead, evidence that TTP, a target of MK2, can also destabilize the IL-8 ARE reporter mRNA is presented. In a comprehensive approach to identify mRNAs controlled by KSRP, two criteria were evaluated by microarray analysis of (i) association of mRNAs with KSRP in pulldown assays and (ii) increased amounts in KSRP knockdown cells. According to both criteria, a group of 100 mRNAs is controlled by KSRP, many of which are unstable and encode proteins involved in inflammation. These results indicate that KSRP functions as a limiting factor in inflammatory gene expression.

Transcriptional activation of MMP-13 by periodontal pathogenic LPS requires p38 MAP kinase

Matrix metalloprotease-13 (MMP-13) is induced by pro-inflammatory cytokines and increased expression is associated with a number of pathological conditions such as tumor metastasis, osteoarthritis, rheumatoid arthritis and periodontal diseases. MMP-13 gene regulation and the signal transduction pathways activated in response to bacterial LPS are largely unknown. In these studies, the role of the mitogen-activated protein kinase (MAPK) pathways in the regulation of MMP-13 induced by lipopolysaccharide was investigated. Lipopolysaccharide from Escherichia coli and Actinobacillus actinomycetemcomitans significantly (P < 0.05) increased MMP-13 steady-state mRNA (average of 27% and 46% increase, respectively) in murine periodontal ligament fibroblasts. MMP-13 mRNA induction was significantly reduced by inhibition of p38 MAP kinase. Immunoblot analysis indicated that p38 signaling was required for LPS-induced MMP-13 expression. Lipopolysaccharide induced proximal promoter reporter (-660/+32 mMMP-13) gene activity required p38 signaling. Collectively, these results indicate that lipopolysaccharide-induced murine MMP-13 is regulated by p38 signaling through a transcriptional mechanism.

Regulation of matrix metalloproteinase gene expression

The metalloproteinases degrade extracellular matrix (ECM) components and activate growth factors, thereby contributing to physiological events (tissue remodeling in pregnancy, wound healing, angiogenesis) and pathological conditions (cancer, arthritis, periodontitis). The intent of this review is to bring together various studies on transcriptional and post-transcriptional control of metalloproteinase expression. Certainly, much information is known as to the cis-elements and corresponding trans-activators regulating expression of these genes. We discuss the fact that a number of the metalloproteinase promoters share common structural features and, therefore, not surprisingly are co-regulated in their expression to some extent. More recently, much effort has been devoted to understanding the role of chromatin in regulating gene expression. While this area has been understudied with respect to matrix metalloproteinase (MMP) regulation, the literature indicates a convincing role for both histone modifications and chromatin-remodeling motors in controlling expression of multiple metalloproteinases. In addition to transcriptional control, mRNA stability and protein translation also contribute to the metalloproteinase product amount. We discuss such studies and how various biological cues, including TGF-beta, regulate the levels of certain collagenases either solely through mRNA stabilization or by jointly targeting transcriptional and post-transcriptional mechanisms. We also discuss the current deficits in our knowledge, concerning tissue-specific expression and why despite elevated amounts/activity of trans-activators targeting MMP promoters in tumor cells, nevertheless, MMP expression is largely restricted to the stromal compartment. Finally, we argue for potential technologies to regulate MMP expression of utility in pathological conditions where these enzymes are aberrantly expressed.

Stability and translation of TCR zeta mRNA are regulated by the adenosine-uridine-rich elements in splice-deleted 3' untranslated region of zeta-chain

Systemic lupus erythematosus (SLE) T cells display reduced expression of TCR zeta protein. Recently, we reported that in SLE T cells, the residual TCR zeta protein is predominantly derived from an alternatively spliced form that undergoes splice deletion of 562 nt (from 672 to 1233 bases) within the 3' untranslated region (UTR) of TCR zeta mRNA. The stability and translation of the alternatively spliced form of TCR zeta mRNA are low compared with that of the wild-type TCR zeta mRNA. We report that two adenosine-uridine-rich sequence elements (AREs), defined by the splice-deleted 3' UTR region, but not an ARE located upstream are responsible for securing TCR zeta mRNA stability and translation. The stabilizing effect of the splice-deleted region-defined AREs extended to the luciferase mRNA and was not cell type-specific. The findings demonstrate distinct sequences within the splice-deleted region 672 to 1233 of the 3' UTR, which regulate the transcription, mRNA stability, and translation of TCR zeta mRNA. The absence of these sequences represents a molecular mechanism that contributes to altered TCR zeta-chain expression in lupus.

FBPs are calibrated molecular tools to adjust gene expression

The three far-upstream element (FUSE) binding protein (FBP) family members have been ascribed different functions in gene regulation. They were therefore examined with various biochemical, molecular biological, and cell biological tests to evaluate whether their sequence differences reflect functional customization or neutral changes at unselected residues. Each FBP displayed a characteristic profile of intrinsic transcription activation and repression, binding with protein partners, and subcellular trafficking. Although some differences, such as weakened FBP3 nuclear localization, were predictable from primary sequence differences, the unexpected failure of FBP3 to bind the FBP-interacting repressor (FIR) was traced to seemingly conservative substitutions within a small patch of an N-terminal alpha-helix. The transactivation strength and the FIR-binding strength of the FBPs were in the opposite order. Despite their distinguishing features and differential activities, the FBPs traffic to shared subnuclear sites and regulate many common target genes, including c-myc. Though a variety of functions have been attributed to the FBPs, based upon their panel of shared and unique features, we propose that they constitute a molecular regulatory kit that tunes the expression of shared targets through a common mechanism.

Spontaneous rescue from cystic fibrosis in a mouse model

BACKGROUND

From the original CftrTgH(neoim)Hgu mutant mouse model with a divergent genetic background (129P2, C57BL/6, MF1) we have generated two inbred CftrTgH(neoim)Hgu mutant strains named CF/1-CftrTgH(neoim)Hgu and CF/3-CftrTgH(neoim)Hgu, which are fertile and show normal growth and lifespan. Initial genome wide scan analysis with microsatellite markers indicated that the two inbred strains differed on the genetic level. In order to further investigate whether these genetic differences have an impact on the disease phenotype of cystic fibrosis we characterised the phenotype of the two inbred strains.

RESULTS

Reduced amounts, compared to wild type control animals, of correctly spliced Cftr mRNA were detected in the nasal epithelia, lungs and the intestine of both inbred CftrTgH(neoim)Hgu strains, with higher residual amount observed for CF/1-CftrTgH(neoim)Hgu than CF/3-CftrTgH(neoim)Hgu for every investigated tissue. Accordingly the amounts of wild type Cftr protein in the intestine were 9% for CF/1-CftrTgH(neoim)Hgu and 4% for CF/3-CftrTgH(neoim)Hgu. Unlike the apparent strain and/or tissue specific regulation of Cftr mRNA splicing, short circuit current measurements in the respiratory and intestinal epithelium revealed that both strains have ameliorated the basic defect of cystic fibrosis with a presentation of a normal electrophysiology in both tissues.

CONCLUSION

Unlike the outbred CftrTgH(neoim)Hgu insertional mouse model, which displayed the electrophysiological defect in the gastrointestinal and respiratory tracts characteristic of cystic fibrosis, both inbred CftrTgH(neoim)Hgu strains have ameliorated the electrophysiological defect. On the basis of these findings both CF/1-CftrTgH(neoim)Hgu and CF/3-CftrTgH(neoim)Hgu offer an excellent model whereby determination of the minimal levels of protein required for the restoration of the basic defect of cystic fibrosis can be studied, along with the modulating factors which may affect this outcome.

Mechanisms of glucocorticoid action in bone

Glucocorticoids induce rapid bone loss and increase the risk for osteoporotic fractures. The mechanisms include a phase of increased bone resorption, probably a result of the increased expression of receptor activator of nuclear factor-k-B ligand and colony stimulating factor-1, followed-up by a decrease in bone formation. This effect is central to the actions of glucocorticoids in bone and it is secondary to the loss of bone forming cells, caused by an inhibition of cell differentiation and an increase in the apoptosis of mature osteoblasts and osteocytes. Glucocorticoids also inhibit the function of mature osteoblasts and suppress the synthesis of insulin-like growth factor-I, an agent that enhances bone formation. Glucocorticoids alter the growth hormone/insulin-like growth factor axis in cartilage and, as a consequence, suppress linear growth.

Collagenases in cancer

Three mammalian collagenases (MMP-1, MMP-8, and MMP-13) belong to family of matrix metalloproteinases and are the principal secreted endopeptidases capable of cleaving collagenous extracellular matrix. In addition to fibrillar collagens, collagenases can cleave several other matrix and non-matrix proteins including growth factors, and this way regulate cell growth and survival. Collagenases are important proteolytic tools for extracellular matrix remodeling during organ development and tissue regeneration, but they also apparently play important roles in many pathological situations and tumor progression and metastasis. Because of their potentially destructive characteristics the expression and activity of collagenases are strictly controlled. Synthesis of collagenases is regulated by extracellular signals via cellular signal transduction pathways at transcriptional and post-transcriptional level. Collagenases are synthesized as inactive pro-forms, and once activated, their activity is inhibited by specific tissue inhibitors of metalloproteinases, TIMPs, as well as by non-specific proteinase inhibitors. In this review we discuss the current view on the role of collagenases in tumor growth, invasion, and metastasis, as a basis for their feasibility in diagnosis and prognostication, as well as therapeutic targets in cancer patients.

MKK3/6-p38 MAPK negatively regulates murine MMP-13 gene expression induced by IL-1beta and TNF-alpha in immortalized periodontal ligament fibroblasts

Matrix metalloprotease-13 (MMP-13) or collagenase-3 is involved in a number of pathologic processes such as tumor metastasis and angiogenesis, osteoarthritis, rheumatoid arthritis and periodontal diseases. These conditions are associated with extensive degradation of both connective tissue and bone. This report examines gene regulation mechanisms and signal transduction pathways involved in Mmp-13 expression induced by proinflammatory cytokines in periodontal ligament (PDL) fibroblasts. Mmp-13 mRNA expression was increased 10.7 and 9.5 fold after stimulation with IL-1beta (5 ng/mL) and TNF-alpha (10 ng/mL), respectively. However, inhibition of p38 MAPKinase with SB203580 resulted in significant (p<0.001) induction (23.2 and 18.1 fold, respectively) of Mmp-13 mRNA as assessed by real time PCR. Negative regulation of IL-1beta induced Mmp-13 expression was confirmed by inhibiting p38 MAPK gene expression with siRNA. Transient transfection of dominant negative forms of MKK3 and MKK6 also resulted in increased levels of Mmp-13 mRNA after IL-1beta stimulation. Mmp-13 mRNA expression induced by TNF-alpha was decreased by JNK and ERK inhibition. Western blot and zymogram analysis indicated that Mmp-13 protein expression induced by the proinflammatory cytokines were also upregulated by inhibition of p38 MAPK. Reporter gene experiments using stable cell lines harboring 660-bp sequence of the murine Mmp-13 proximal promoter indicated that transcriptional mechanisms were at least partially involved in this negative regulation of Mmp-13 expression by p38 MAPK and upstream MKK3/6. These results suggest a negative transcriptional regulatory mechanism mediated by p38 MAPK and upstream MKK3/6 on Mmp-13 expression induced by proinflammatory cytokines in PDL fibroblasts.

IL-1beta induces stabilization of IL-8 mRNA in malignant breast cancer cells via the 3' untranslated region: Involvement of divergent RNA-binding factors HuR, KSRP and TIAR

IL-8 plays an integral role in promoting the malignant phenotype in breast cancer, and its production is directly influenced by inflammatory cytokines in the tumor microenvironment. Here, we show that activation of IL-1beta receptors on malignant HS578t and MDA-MB-231 breast cancer cells strongly induces IL-8 expression and that RNA stabilization is persistently activated at least 12-24 hr after stimulation. SB 203580 and rapamycin reversed the RNA stabilization effect of IL-1beta in a dose-dependent manner, suggesting involvement of the p38/MAP kinase and mTOR pathways. A luciferase reporter assay indicated that the stabilization effect was dependent on cis elements in the 3'-untranslated region (UTR) of the IL-8 transcript. By UV cross-linking, we identified multiple cellular factors that interact with the IL-8 3'UTR, ranging 34-76 kDa. Immunoprecipitation analysis indicated that HuR, KSRP and TIAR bound to one or more loci in the 3'UTR. While the cross-linking patterns were similar, quantitative immunoprecipitation of native IL-8 RNA from IL-1beta-stimulated cytoplasmic extract revealed a 20-fold greater association of transcript with the stabilizing factor HuR vs. the destabilizing factor KSRP. In conclusion, IL-1beta is a potent cytokine stimulus for IL-8 RNA stabilization in breast cancer cells, possibly by enhanced binding of cytoplasmic HuR to the 3'UTR.

Decreased stability and translation of T cell receptor zeta mRNA with an alternatively spliced 3'-untranslated region contribute to zeta chain down-regulation in patients with systemic lupus erythematosus

The molecular mechanisms involved in the aberrant expression of T cell receptor (TCR) zeta chain of patients with systemic lupus erythematosus are not known. Previously we demonstrated that although normal T cells express high levels of TCR zeta mRNA with wild-type (WT) 3' untranslated region (3' UTR), systemic lupus erythematosus T cells display significantly high levels of TCR zeta mRNA with the alternatively spliced (AS) 3' UTR form, which is derived by splice deletion of nucleotides 672-1233 of the TCR zeta transcript. Here we report that the stability of TCR zeta mRNA with an AS 3' UTR is low compared with TCR zeta mRNA with WT 3' UTR. AS 3' UTR, but not WT 3' UTR, conferred similar instability to the luciferase gene. Immunoblotting of cell lysates derived from transfected COS-7 cells demonstrated that TCR zeta with AS 3' UTR produced low amounts of 16-kDa protein. In vitro transcription and translation also produced low amounts of protein from TCR zeta with AS 3' UTR. Taken together our findings suggest that nucleotides 672-1233 bp of TCR zeta 3' UTR play a critical role in its stability and also have elements required for the translational regulation of TCR zeta chain expression in human T cells.

Transforming growth factor-beta 1 regulation of collagenase-3 expression in osteoblastic cells by cross-talk between the Smad and MAPK signaling pathways and their components, Smad2 and Runx2

Transforming growth factor-beta (TGF-beta) plays a key role in osteoblast differentiation and bone development and remodeling. Collagenase-3 (matrix metalloproteinase-13) is expressed by osteoblasts and seems to be involved in osteoclastic bone resorption. Here, we show that TGF-beta 1 stimulates collagenase-3 expression in the rat osteoblastic cell line UMR 106-01 and requires de novo protein synthesis. Dominant-negative Smad2/3 constructs indicated that Smad signaling is essential for TGF-beta 1-stimulated collagenase-3 promoter activity. Inhibitors of the ERK1/2 and p38 MAPK pathways, but not the JNK pathway, reduced TGF-beta 1-stimulated collagenase-3 expression, indicating that the p38 MAPK and ERK1/2 pathways are also required for TGF-beta 1-stimulated collagenase-3 expression in UMR 106-01 cells. These inhibitors did not prevent nuclear localization of Smad proteins, but they inhibited Smad-mediated transcriptional activation. We have shown for the first time that Runx2 (a bone transcription factor and a potential substrate for the MAPK pathway) is phosphorylated in response to TGF-beta 1 treatment in osteoblastic cells. Cotransfection of Smad2 and Runx2 constructs had a cooperative effect on TGF-beta 1-stimulated collagenase-3 promoter activity in these cells. We further identified ligand-independent physical interaction between Smad2 and Runx2. Taken together, our results provide an important role for cross-talk between the Smad and MAPK pathways and their components in expression of collagenase-3 following TGF-beta 1 treatment in UMR 106-01 cells.