Expression of P-450 enzyme activities in heterologous cells by transfection

Nuclear receptor crosstalk - defining the mechanisms for therapeutic innovation

Nuclear receptor crosstalk can be defined as the interplay between different nuclear receptors or between their overlapping signalling pathways. A subset of nuclear receptors (such as PPARs and RARs) engage in the formation of well-characterized 'typical' heterodimers with RXR. 'Atypical' heterodimers (such as GR with PPARs, or PPAR with ERR) might form a novel class of physical complexes that might be more transient in nature. These heterodimers might harbour strong transcriptional flexibility, with no strict need for DNA binding of both partners. Direct crosstalk could stem from a pairwise physical association between atypical nuclear receptor heterodimers, either via pre-existing interaction pairs or via interactions that are newly induced with small molecules; such crosstalk might constitute an uncharted space to target nuclear receptor physiological and/or pathophysiological actions. In this Review, we discuss the emerging aspects of crosstalk in the nuclear receptor field and present various mechanistic crosstalk modes with examples that support applicability of the atypical heterodimer concept. Stabilization or disruption, in a context-dependent or cell type-dependent manner, of these more transient heterodimers is expected to fuel unprecedented translational approaches to yield novel therapeutic agents to treat major human diseases with higher precision.

Immunolocalization of 3β-hydroxysteroid dehydrogenase in human adrenal cortex and in its disorders

Immunohistochemical localization of 3β-hydroxysteroid dehydrogenase/Δ^5→4-isomerase (3β-HSD), which converts Δ⁵-3β-hydroxysteroids to Δ⁴-3-ketosteroids, was performed in the human adrenal gland and in its disorders by employing a specific antibody raised against the enzyme purified from human placenta. Immunoreactivity of 3β-HSD was present in all three cortical zones of the adrenal glands obtained at autopsy, while in surgically removed adrenal glands, immunoreactivity was dominant in the zona fasciculata (ZF), with faint immunoreactivity in the zona glomerulosa (ZG) and the zona reticularis (ZR). Intracortical localization of 3β-HSD in the adrenal glands obtained at autopsy may represent an adrenal adaptation to antemortem stress, with shifting of adrenal pregnenolone- a substrate of 3β-HSD - as well as steroid 17α-hydroxylase from adrenal androgen synthesis to glucocorticoid synthesis. In adrenocortical hyperplasia, marked immunoreactivity was observed in the ZG and outer ZF in adrenal glands with idiopathic hyperaldosteronism and in the ZF and ZR, especially in cortical micronodules, in the adrenal glands associated with Cushing's disease. In aldosteronoma and Cushing's adenoma, immunoreactivity of the enzyme was much more intense in large clear tumor cells than in small compact tumor cells. Immunolocalization of 3β-HSD can yield important information toward an understanding of adrenal steroid metabolism in both physiological and pathological processes.