Reviews of Physiology Biochemistry and Pharmacology

Abstract

During protein translation, a variety of quality control checks ensure that the resulting polypeptides deviate minimally from their genetic encoding template. Translational fidelity is central in order to preserve the function and integrity of each cell. Correct termination is an important aspect of translational fidelity, and a multitude of mechanisms and players participate in this exquisitely regulated process. This review explores our current understanding of eukaryotic termination by highlighting the roles of the different ribosomal components as well as termination factors and ribosome-associated proteins, such as chaperones.Abbreviations aa-tRNA: Amino-acyl tRNA · eLF: Eukaryotic translation initiation factor · IF: Prokaryotic translation initiation factor · eEF: Eukaryotic translation elongation factor · EF: Prokaryotic translation elongation factor · eRF: Eukaryotic translation termination factor (release factor) · RF: Prokaryotic translation release factor · RRF: Ribosome recycling factor · Rps: Protein of the prokaryotic small ribosomal subunit · Rpl: Protein of the eukaryotic large ribosomal subunit · S: Protein of the prokaryotic small ribosomal subunit · L: Protein of the prokaryotic large ribosomal subunit · PTC: Peptidyl transferase center · RNC: Ribosome-nascent chain-mRNA complex · ram: Ribosomal ambiguity mutation · RAC: Ribosome-associated complex · NMD: Nonsense-mediated mRNA decay Abstract The aquaporins (AQPs) are small integral membrane proteins that transport water and in some cases small solutes such as glycerol. Physiological roles of the ten or more mammalian AQPs have been proposed based on their expression in epithelial, endothelial and other tissues, their regulation, and in some cases the existence of humans with AQP mutation. Here, the role of AQPs in mammalian physiology is reviewed, based on phenotype analysis of transgenic mouse models of AQP deletion/mutation. Phenotype studies support the predicted roles of AQPs in kidney tubule and microvessel fluid transport for urinary concentrating function, and in fluid-secreting glandular epithelia. The phenotype studies have also shown unexpected roles of AQPs in brain and corneal swelling, in neural signal transduction, in regulation of intracranial and intraocular pressure, and in tumor angiogenesis and cell migration. The water/glycerol-transporting AQPs were found to play unexpected roles in skin hydration and in fat metabolism. However, many phenotype studies were negative, such as normal airway/lung and skeletal muscle function, despite AQP expression, indicating that tissue-specific AQP expression does not indicate physiological significance. The mouse phenotype data suggest that modulators of AQP expression/function may have such wide-ranging clinical applications as diuretics and in the treatment of brain swelling, glaucoma, epilepsy, obesity, and cancer. Rev Physiol Biochem Pharmacol (2005) 155:57-80 Abstract Heterotrimeric G-proteins are key transducers for signal transfer from outside the cell, mediating signals emanating...

AQP5 regulates the proliferation and differentiation of epidermal stem cells in skin aging

“…Aquaporins (AQPs) are a family of homologous waterand glycerol-transporting proteins expressed in many mammalian epithelial, endothelial, and other types of cells. AQPs have shown to play a role in transcellular permeability in many organisms (11,12). For example, AQPs play a role in secretory glands, such as salivary (13,14), lacrimal (15), and sweat (16) glands, and pancreatic (17,18) glands, and their role in secretory glands has been evaluated in AQP-null mice.…”