Inhibition of the activation of hepatic stellate cells by arundic acid via the induction of cytoglobin

BackgroundThe activation of hepatic stellate cells plays a central role in the development of liver fibrosis during chronic liver trauma. The aim of the present study was to identify a compound that inhibits the activation process of stellate cells.MethodsRat primary cultured stellate cells and a human stellate cell line (LX-2) were used. The effects of arundic acid on the expression of α-smooth muscle actin, collagen 1α1, and cytoglobin were evaluated.ResultsArundic acid (300 μM) inhibited the activation of primary rat stellate cells, as determined by morphological transformation and α-smooth muscle actin expression, after both prophylactic and therapeutic treatment. The level of α-smooth muscle actin mRNA showed a dose-dependent decrease in response to arundic acid, and 50 μM arundic acid exhibited the maximum inhibition of collagen 1α1 mRNA expression. In contrast, arundic acid triggered an unexpected increase in mRNA and protein levels of cytoglobin, the fourth globin in mammals expressed exclusively in hepatic stellate cells. The effect of arundic acid on the level of α-smooth muscle actin mRNA was abrogated in HSCs treated with cytoglobin siRNA. Arundic acid decreased the expression of collagen 1α1 mRNA in LX-2 cells.ConclusionArundic acid affects the activation process of hepatic stellate cells via the unexpected induction of cytoglobin.     

Aspartyl aminopeptidase is imported from the cytoplasm to the vacuole by selective autophagy in Saccharomyces cerevisiae

Macroautophagy is a catabolic process by which cytosolic components are sequestered by double membrane vesicles called autophagosomes and sorted to the lysosomes/vacuoles to be degraded. Saccharomyces cerevisiae has adapted this mechanism for constitutive transport of the specific vacuolar hydrolases aminopeptidase I (Ape1) and α-mannosidase (Ams1); this process is called the cytoplasm to vacuole targeting (Cvt) pathway. The precursor form of Ape1 self-assembles into an aggregate-like structure in the cytosol that is then recognized by Atg19 in a propeptide-dependent manner. The interaction between Atg19 and autophagosome-forming machineries allows selective packaging of the Ape1-Atg19 complex by the autophagosome-like Cvt vesicle. Ams1 also forms oligomers and utilizes the Ape1 transport system by interacting with Atg19. Although the mechanism of selective transport of the Cvt cargoes has been well studied, it is unclear whether proteins other than Ape1 and Ams1 are transported via the Cvt pathway. We describe here that aspartyl aminopeptidase (Yhr113w/Ape4) is the third Cvt cargo, which is similar in primary structure and subunit organization to Ape1. Ape4 has no propeptide, and it does not self-assemble into aggregates. However, it binds to Atg19 in a site distinct from the Ape1- and Ams1-binding sites, allowing it to "piggyback" on the Ape1 transport system. In growing conditions, a small portion of Ape4 localizes in the vacuole, but its vacuolar transport is accelerated by nutrient starvation, and it stably resides in the vacuole lumen. We propose that the cytosolic Ape4 is redistributed to the vacuole when yeast cells need more active vacuolar degradation.     

Involvement of ERK1/2 activation in the gene expression of senescence-associated secretory factors in human hepatic stellate cells

Molecular and Cellular Biochemistry - Senescent hepatic stellate cells (senescent HSCs) are found in patients with liver cirrhosis and have been thought to be involved in the development of...     

Defining microbial community composition and seasonal variation in a sewage treatment plant in India using a down-flow hanging sponge reactor

Applied Microbiology and Biotechnology - The characteristics of the microbial community in a practical-scale down-flow hanging sponge (DHS) reactor, high in organic matter and sulfate ion...     

Ligand-induced downregulation of TrkA is partly regulated through ubiquitination by Cbl

Nerve growth factor (NGF) binding to its receptor TrkA, which belongs to the family of receptor tyrosine kinases (RTKs), is known to induce its internalization, endosomal trafficking and subsequent lysosomal degradation. The Cbl family of ubiquitin ligases plays a major role in mediating ubiquitination and degradation of RTKs. However, it is not known whether Cbl participates in mediating ubiquitination of TrkA. Here we report that c-Cbl mediates ligand-induced ubiquitination and degradation of TrkA. TrkA ubiquitination and degradation required direct interactions between c-Cbl and phosphorylated TrkA. c-Cbl and ubiquitinated TrkA are found in a complex after NGF stimulation and are degraded in lysosomes. Taken together, our data demonstrate that c-Cbl can induce downregulation of NGF-TrkA complexes through ubiquitination and degradation of TrkA.