Regulation of the methylation status of G protein-coupled receptor kinase 1 (rhodopsin kinase)

An Anatomy of Fungal Eye: Fungal Photoreceptors and Signalling Mechanisms

Organisms have developed different features to capture or sense sunlight. Vertebrates have evolved specialized organs (eyes) which contain a variety of photosensor cells that help them to see the light to aid orientation. Opsins are major photoreceptors found in the vertebrate eye. Fungi, with more than five million estimated members, represent an important clade of living organisms which have important functions for the sustainability of life on our planet. Light signalling regulates a range of developmental and metabolic processes including asexual sporulation, sexual fruit body formation, pigment and carotenoid production and even production of secondary metabolites. Fungi have adopted three groups of photoreceptors: (I) blue light receptors, White Collars, vivid, cryptochromes, blue F proteins and DNA photolyases, (II) red light sensors, phytochromes and (III) green light sensors and microbial rhodopsins. Most mechanistic data were elucidated on the roles of the White Collar Complex (WCC) and the phytochromes in the fungal kingdom. The WCC acts as both photoreceptor and transcription factor by binding to target genes, whereas the phytochrome initiates a cascade of signalling by using mitogen-activated protein kinases to elicit its cellular responses. Although the mechanism of photoreception has been studied in great detail, fungal photoreception has not been compared with vertebrate vision. Therefore, this review will mainly focus on mechanistic findings derived from two model organisms, namely Aspergillus nidulans and Neurospora crassa and comparison of some mechanisms with vertebrate vision. Our focus will be on the way light signalling is translated into changes in gene expression, which influences morphogenesis and metabolism in fungi.

Polyisoprenylated methylated protein methyl esterase is both sensitive to curcumin and overexpressed in colorectal cancer: implications for chemoprevention and treatment

Inhibition of PMPMEase, a key enzyme in the polyisoprenylation pathway, induces cancer cell death. In this study, purified PMPMEase was inhibited by the chemopreventive agent, curcumin, with a K(i) of 0.3 μM (IC50 = 12.4 μM). Preincubation of PMPMEase with 1 mM curcumin followed by gel-filtration chromatography resulted in recovery of the enzyme activity, indicative of reversible inhibition. Kinetics analysis with N-para-nitrobenzoyl-S-trans,trans-farnesylcysteine methyl ester substrate yielded K M values of 23.6 ± 2.7 and 85.3 ± 15.3 μM in the absence or presence of 20 μM curcumin, respectively. Treatment of colorectal cancer (Caco2) cells with curcumin resulted in concentration-dependent cell death with an EC50 of 22.0 μg/mL. PMPMEase activity in the curcumin-treated cell lysate followed a similar concentration-dependent profile with IC50 of 22.6 μg/mL. In colorectal cancer tissue microarray studies, PMPMEase immunoreactivity was significantly higher in 88.6% of cases compared to normal colon tissues (P < 0.0001). The mean scores ± SEM were 91.7 ± 11.4 (normal), 75.0 ± 14.4 (normal adjacent), 294.8 ± 7.8 (adenocarcinoma), and 310.0 ± 22.6 (mucinous adenocarcinoma), respectively. PMPMEase overexpression in colorectal cancer and cancer cell death stemming from its inhibition is an indication of its possible role in cancer progression and a target for chemopreventive agents.