Mechanistic Scrutiny Identifies a Kinetic Role for Cytochrome b5 Regulation of Human Cytochrome P450c17 (CYP17A1, P450 17A1).

Cytochrome P450c17 (P450 17A1, CYP17A1) is a critical enzyme in the synthesis of androgens and is now a target enzyme for the treatment of prostate cancer. Cytochrome P450c17 can exhibit either one or two physiological enzymatic activities differentially regulated by cytochrome b5. How this is achieved remains unknown.

Organization of cytochrome P450 enzymes involved in sex steroid synthesis: PROTEIN-PROTEIN INTERACTIONS IN LIPID MEMBRANES.

Mounting evidence underscores the importance of protein-protein interactions in the functional regulation of drug-metabolizing P450s, but few studies have been conducted in membrane environments, and none have examined P450s catalyzing sex steroid synthesis. Here we report specific protein-protein interactions for full-length, human, wild type steroidogenic cytochrome P450 (P450, CYP) enzymes: 17alpha-hydroxylase/17,20-lyase (P450c17, CYP17) and aromatase (P450arom, CYP19), as well as their electron donor NADPH-cytochrome P450 oxidoreductase (CPR). Fluorescence resonance energy transfer (FRET)(3) in live cells, coupled with quartz crystal microbalance (QCM), and atomic force microscopy (AFM) studies on phosphatidyl choline +/- cholesterol (mammalian) biomimetic membranes were used to investigate steroidogenic P450 interactions.

The developmental increase in adrenocortical 17,20-lyase activity (biochemical adrenarche) is driven primarily by increasing cytochrome b5 in neonatal rhesus macaques.

Adrenarche is thought to be experienced only by humans and some Old World primates despite observed regression of an adrenal fetal zone and establishment of a functional zona reticularis (ZR) in other species like rhesus macaques. Adrenal differentiation remains poorly defined biochemically in nonhuman primates. The present studies defined ZR development in the neonatal rhesus by examining androgen synthetic capacity and factors affecting it in rhesus and marmoset adrenals.

Morphological adrenarche in rhesus macaques: development of the zona reticularis is concurrent with fetal zone regression in the early neonatal period.

Human adrenarche is associated with the establishment of a functional zona reticularis (ZR) and increasing secretion of dehydroepiandrosterone (DHEA) in sulfated form (DS). Like most non-human primates, rhesus macaques are not believed to undergo adrenarche, though they clearly establish a functional ZR after birth. However, the origins of the rhesus ZR are not well defined.

Adrenal androgens in humans and nonhuman primates: production, zonation and regulation.

The synthesis and secretion of large quantities of the adrenal androgens, dehydroepiandrosterone (DHEA) and its sulfoconjugate DHEA sulfate (DS), is a phenomenon that appears limited to humans and some nonhuman primates. Both hydroxylase and lyase activities of the enzyme 17alpha-hydroxylase/17,20-lyase cytochrome P450 (P450c17) are necessary for DHEA production and are differentially regulated during adrenal development. Production of DHEA and DS occurs in the zona reticularis (ZR) of adults and the fetal zone of fetal primate adrenal glands, which is the primary substrate for maternal estrogen production during pregnancy.

Gender and gonadal status differences in zona reticularis expression in marmoset monkey adrenals: Cytochrome b5 localization with respect to cytochrome P450 17,20-lyase activity.

Neonatal marmosets express an adrenal fetal zone comparable to humans. While adult males fail to express a functional ZR, with barely detectable blood DHEA levels, females produce higher levels of DHEA than males in adulthood. We investigated the presence of a putative functional ZR in adult female marmosets.

Male marmoset monkeys express an adrenal fetal zone at birth, but not a zona reticularis in adulthood.

Neonatal human males produce high levels of dehydroepiandrosterone (DHEA) and its sulfo-conjugated form (DS) that decline within a few months of birth, due to regression of the adrenal fetal zone (FZ). Adult male humans and rhesus monkeys produce C19 steroids in abundance from the adrenal zona reticularis (ZR). Male marmoset monkeys produce DS at birth, but unlike humans and rhesus monkeys, do not produce comparable amounts of DHEA and DS in adulthood.