Localisation of lanosterol 14alpha-demethylase in round and elongated spermatids of the mouse testis: an immunoelectron microscopic and stereological study

Human cytochrome P450 enzymes 5-51 as targets of drugs and natural and environmental compounds: mechanisms, induction, and inhibition - toxic effects and benefits

Cytochrome P450 (P450, CYP) enzymes have long been of interest due to their roles in the metabolism of drugs, pesticides, pro-carcinogens, and other xenobiotic chemicals. They have also been of interest due to their very critical roles in the biosynthesis and metabolism of steroids, vitamins, and certain eicosanoids. This review covers the 22 (of the total of 57) human P450s in Families 5-51 and their substrate selectivity. Furthermore, included is information and references regarding inducibility, inhibition, and (in some cases) stimulation by chemicals. We update and discuss important aspects of each of these 22 P450s and questions that remain open.

Germ cell-specific localization of immunoreactive riboflavin carrier protein in the male golden hamster: appearance during spermatogenesis and role in sperm function

Riboflavin carrier protein (RCP) is a phosphoglycoprotein (37 kDa) that is well studied in chicken. An immunologically cross-reacting protein was identified in mammals and active immunization of male rats and bonnet monkeys with chicken RCP lead to an approximately 80% reduction in fertility. However, the physiological mechanism responsible for inhibition of male fertility has not been investigated. Moreover, information on the cell type-specific localization and the origin of immunoreactive RCP during spermatogenesis is extremely limited. Hence, studies were carried out to determine the pattern of expression of immunoreactive RCP during spermatogenesis and its role in sperm function in the golden hamster. Immunoreactive RCP was germ cell-specific, found to be associated with the acrosome-organizing region of early spermatids and showed interesting patterns of immunolocalization during late stages of spermiogenesis. Mature spermatozoa exhibited acrosome-specific localization, mainly in the peri-acrosomal membrane. The immunoreactive protein was undetectable in (non)gonadal somatic cells tested. The protein had a molecular mass of 45-55 kDa and was biosynthesized by round spermatids. The acrosome-specific localization of immunoreactive RCP was unchanged during capacitation, but it was substantially lost during acrosome reaction. Functional studies indicated that treatment of spermatozoa with anti-RCP antibodies did not have any effect on either capacitation or acrosome reaction, but markedly reduced the rate of sperm penetration into zona-free hamster oocytes. These results show the existence of male germ cell-specific immunoreactive RCP, having a potential role in sperm-egg interaction in hamsters. Also the pattern of immunoreactive-RCP localization makes it an ideal marker to monitor development of acrosome in mammalian spermatozoa.

Many facets of mammalian lanosterol 14alpha-demethylase from the evolutionarily conserved cytochrome P450 family CYP51

Lanosterol 14alpha-demethylase is a cytochrome P450 enzyme of the cholesterol biosynthetic pathway belonging to the CYP51 gene family which is the most evolutionarily conserved member of the CYP superfamily. Mammalian (human, mouse, rat, pig) CYP51 genes are unique in sharing several common characteristics: highly conserved exon/intron borders and proximal promoter structures, ubiquitous expression at the highest level in the testis, and appearance of testis-specific transcripts that arise from differential polyadenylation site usage. CYP51 protein demethylates lanosterol to form follicular fluid meiosis-activating sterol, FF-MAS, which is, besides being an intermediate of cholesterol biosynthesis, also a signaling sterol that accumulates in ovaries. CYP51 protein resides in the endoplasmatic reticulum of most cells and also in acrosomal membranes of spermatids where transport through the Golgi apparatus is suggested. While sterol regulatory element binding protein (SREBP)-dependent transcriptional regulation of CYP51 contributes to synthesis of cholesterol, the germ-cell-specific cAMP/CREMtau-dependent upregulation might contribute to increased production of MAS.

Lanosterol 14alpha-demethylase and MAS sterols in mammalian gametogenesis

The lanosterol 14alpha-demethylase protein complex is composed of a cytochrome P450 enzyme CYP51 and its redox partner NADPH cytochrome P450 reductase. The complex participates in cholesterol biosynthesis and produces folicular fluid meiosis activating sterol (FF-MAS) from lanosterol. FF-MAS is metabolized further by sterol Delta14-reductase to testis-meiosis activating sterol (T-MAS). Additional enzymatic steps are needed before cholesterol is produced. Using the anti-human CYP51 antibody we have studied CYP51 protein expression by confocal microscopy in male and female mouse gonads. Leydig cells and acrosomes of spermatids express the highest levels of the CYP51 protein. CYP51 protein is also detected in primary mouse oocytes of non-treated mice and in some granulosa cells. While regulatory mechanisms responsible for FF-MAS accumulation in the ovary are not yet established, two mechanisms contributing to production the of T-MAS in the testis have been found. Potential in vivo roles of FF-MAS and T-MAS in fertilization are discussed.