Biliverdin reductase: new features of an old enzyme and its potential therapeutic significance.

Biliverdin reductase (BVR) was known for a long time solely as an enzyme converting biliverdin to bilirubin, the major physiological antioxidant. Recent years revealed unique features of this protein which are not related to its reductase activity. The most intriguing and surprising finding is its dual-specificity kinase character. As such serine/threonine/tyrosine kinase BVR is involved in regulation of glucose metabolism or in control of cell growth and apoptosis. In consequence, it may play a role in pathogenesis of many diseases, such as diabetes or cancers. Moreover, in the nucleus BVR, being a leucine zipper-like DNA binding protein, can act as a transcription factor for activator protein 1 (AP-1)-regulated genes. It has been shown that BVR modulates ATF-2 and HO-1 expression, what suggests its potential role in control of AP-1 and cAMP-regulated genes. In conclusion, BVR together with its substrate, biliverdin, and product, bilirubin, are revealed to be important players in cellular signal transduction pathways, gene expression and oxidative response. These features make BVR unusually interesting and unique among all enzymes characterized to date.

Validation of a rapid, non-radioactive method to quantify internalisation of G-protein coupled receptors.

Agonist exposure can cause internalisation of G-protein coupled receptors (GPCRs), which may be a part of desensitisation but also of cellular signaling. Previous methods to study internalisation have been tedious or only poorly quantitative. Therefore, we have developed and validated a quantitative method using a sphingosine-1-phosphate (S1P) receptor as a model. Because of a lack of suitable binding studies, it has been difficult to study S1P receptor internalisation. Using a N-terminal HisG-tag, S1P(1) receptors on the cell membrane can be visualised via immunocytochemistry with a specific anti-HisG antibody. S1P-induced internalisation was concentration dependent and was quantified using a microplate reader, detecting either absorbance, a fluorescent or luminescent signal, depending on the antibodies used. Among those, the fluorescence detection method was the most convenient to use. The relative ease of this method makes it suitable to measure a large number of data points, e.g. to compare the potency and efficacy of receptor ligands.