Shear stress induces hepatocyte PAI-1 gene expression through cooperative Sp1/Ets-1 activation of transcription
Department of Digestive and General Surgery, Graduate School of Medicine, Niigata University, Niigata, Japan. AJP Gastrointestinal and Liver Physiology
(Impact Factor: 3.8).
08/2006; 291(1):G26-34. DOI: 10.1152/ajpgi.00467.2005
Partial hepatectomy causes hemodynamic changes that increase portal blood flow in the remaining lobe, where the expression of immediate-early genes, including plasminogen activator inhibitor-1 (PAI-1), is induced. We hypothesized that a hyperdynamic circulatory state occurring in the remaining lobe induces immediate-early gene expression. In this study, we investigated whether the mechanical force generated by flowing blood, shear stress, induces PAI-1 expression in hepatocytes. When cultured rat hepatocytes were exposed to flow, PAI-1 mRNA levels began to increase within 3 h, peaked at levels significantly higher than the static control levels, and then gradually decreased. The flow-induced PAI-1 expression was shear stress dependent rather than shear rate dependent and accompanied by increased hepatocyte production of PAI-1 protein. Shear stress increased PAI-1 transcription but did not affect PAI-1 mRNA stability. Functional analysis of the 2.1-kb PAI-1 5'-promoter indicated that a 278-bp segment containing transcription factor Sp1 and Ets-1 consensus sequences was critical to the shear stress-dependent increase of PAI-1 transcription. Mutations of both the Sp1 and Ets-1 consensus sequences, but not of either one alone, markedly prevented basal PAI-1 transcription and abolished the response of the PAI-1 promoter to shear stress. EMSA and chromatin immunoprecipitation assays showed binding of Sp1 and Ets-1 to each consensus sequence under static conditions, which increased in response to shear stress. In conclusion, hepatocyte PAI-1 expression is flow sensitive and transcriptionally regulated by shear stress via cooperative interactions between Sp1 and Ets-1.
Available from: Sheng Zhou
- "Cooperative interactions between Ets1 and Sp1 have been shown to play a critical role in regulating the transcription of many genes, including CTP: phosphocholine cytidylyltransferase α , α11 integrin chain , platelet-derived growth factor D-chain , hepatocyte PA1 , β-1,4-galactosyltransferase V , Runx2  and Guanylyl cyclase/atrial natriuretic peptide receptor . Our data were consistent with the previous studies indicating that Ets1 and Sp1 are transcriptional activators that can stimulate transcription, most likely through cooperative interactions, in this case to enhance expression of the DAXX gene. "
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ABSTRACT: Death-domain-associated protein (DAXX) is a multifunctional protein that regulates a wide range of cellular signaling pathways for both cell survival and apoptosis. Regulation of DAXX gene expression remains largely obscure. We recently reported that berberine (BBR), a natural product derived from a plant used in Chinese herbal medicine, downregulates DAXX expression at the transcriptional level. Here, we further investigate the mechanisms underlying the transcriptional suppression of DAXX by BBR. By analyzing and mapping the putative DAXX gene promoter, we identified the core promoter region (from -161 to -1), which contains consensus sequences for the transcriptional factors Sp1 and Ets1. We confirmed that Sp1 and Ets1 bound to the core promoter region of DAXX and stimulated DAXX transcriptional activity. In contrast, BBR bound to the DAXX core promoter region and suppressed its transcriptional activity. Following studies demonstrated a possible mechanism that BBR inhibited the DAXX promoter activity through blocking or disrupting the association of Sp1 or Ets1 and their consensus sequences in the promoter. Downregulation of DAXX by BBR resulted in inhibition of MDM2 and subsequently, activation of p53, leading to cancer cell death. Our results reveal a novel possible mechanism: by competitively binding to the Sp1 and Ets1 consensus sequences, BBR inhibits the transcription of DAXX, thus inducing cancer cell apoptosis through a p53-dependent pathway.Laboratory Investigation advance online publication, 7 January 2013; doi:10.1038/labinvest.2012.172.
Available from: Joanna Fraczek
- "Too intense cell culture medium flow compromises metabolic functions of hepatocytes and induces significant morphological changes. Moreover, the viability of hepatocytes cultured under high shear conditions is usually lower than that of static controls (Park et al. 2007; Nakatsuka et al. 2006; Powers et al. 2002b; Tanaka et al. 2006). Therefore, it is important to adapt the culture medium flow rates in such a manner that an optimal balance between oxygen/nutrient supply and shear stress level is achieved. "
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ABSTRACT: Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.
Available from: Daniele Mazzei
- "Several reports describe the effects of flow and shear stress on hepatocyte cultures (Mufti and Shuler, 1995; Nakatsuka et al., 2006; Powers et al., 2002b; Tanaka et al., 2006). Moreover, many investigators have shown that the viability of hepatocyte cultures under high shear is usually lower than that of static controls, indicating that the cells are under conditions of stress (Park et al., 2007). "
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ABSTRACT: A generic "system on a plate" modular multicompartmental bioreactor array which enables microwell protocols to be transferred directly to the bioreactor modules, without redesign of cell culture experiments or protocols is described. The modular bioreactors are simple to assemble and use and can be easily compared with standard controls since cell numbers and medium volumes are quite similar. Starting from fluid dynamic and mass transport considerations, a modular bioreactor chamber was first modeled and then fabricated using "milli-molding," a technique adapted from soft lithography. After confirming that the shear stress was extremely low in the system in the range of useful flow rates, the bioreactor chambers were tested using hepatocytes. The results show that the bioreactor chambers can increase or maintain cell viability and function when the flow rates are below 500 microL/min, corresponding to wall shear stresses of 10(-5) Pa or less at the cell culture surface.
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