Receptors for mammalian steroid hormones in microbes and plants

Abstract

Steroids are of universal occurrence, present variously as cell wall constituents and bioregulators. A number of bacteria, fungi, and photosynthetic vascular plants synthesize steroids that are honnonally active in the animal world. The cellular effect of such steroids in microbes and plants appears by and large to be comparable to that in mammals. Available evidence suggests that steroid action in botanical phyla is mediated via receptors organized in a manner similar to that seen in animals. Therefore, the ancestry of ligand induced transactivation via zinc finger proteins appears to date farther back than the early Cambrian burst of metazoan evolution 500 million years ago.Microbe; Plant; Steroid; Hormone; Receptor 1. STEROID DISTRIBUTION AND SYNTHESIS formed to steroids hormonally active in animals and plants [6-81. Receptor mediated control of transcription by steroid hormones (Fig. 1) is a subject of much contemporary interest in mammalian biology. In microbes and plants, the evidence for distribution, synthesis, and physiological action, of steroids has remained rather circumscribed, and sometimes even contradictory. This minireview traces the role played by steroids as messengers at various levels of evolution, as a prelude to understanding receptor origin for further experimental inquiry.Cholesterol is the common starting material in animals for P450 mediated synthesis of all classes of steroid hormones [9]. Plant species have been variously shown to contain glucocorticoids (cortisol), mineralocorticoids (deoxycorticosterone), progestins (progesterone), androgens (testosterone), estrogens (estradiol and estrone) and even the insect moulting hormone ecdysone [2,[5][6][7]10,, as shown in Table I.Life on earth is believed to have originated some 4 billion years ago from about 30 biologically useful precursors, formed from simple inorganic matter under the influence of the cosmic energy reaching our planet. Steroids are of universal occurrence, present in the cell variously as membrane constituents, chemical messengers, vitamins, cytotoxins, and hormones [1,2]. CELLULAR FUNCTION OF STEROIDSWhereas prokaryotic transformation of steroids is rich in diversity [3], the synthesis of sterols follows two major routes in higher organisms [4]. Squalene 2,3-oxide, formed from acetate via common pathways, is cyclized either to lanosterol in non-photosynthetic eukaryotes (fungi, animals), or to cycloartenol in photosynthetic phyla [4]. Insects transform steroids and ster01s ingested during feeding [2]. Plant sterols, saponins, cardiac glycosides, and alkaloids are of much biomedical value, but have no demonstrated counterparts or hormonal role in mammals [5]. Several bacterial and plant species synthesize cholesterol which is then transEarlier studies had shown that bacteria, mycoplasma (PPLO), and fungi respond to sterols and steroids in bewildering ways, ranging from vitamin-like to antimicrobial [7]. Mammalian gonadal hormones generally inhibit the growth of bacteria, in particular the Grampositive organisms [7,11]....

Data analysis in plant physiology: are we missing the reality?

“…This PGR effect is probably not always artifactual because very high concentrations of BS are found in specific organs, such as pollen (Adam & Marquardt 1986). This PGR activity of brassinosteroids is not surprising when it is considered that in unicellular organisms, steroid hormones are involved in the regulation of the cell cycle (Dahl, Biemann & Dahl 1987;Argawal 1993).…”

Conservation of function between mammalian and plant steroid 5α-reductases

“…These receptors achieve their physiological functions by binding to specific DNA sequences termed hormone response elements, thereby activating or suppressing target gene expression in a ligand-dependent manner (29). Steroid-binding proteins that exhibit high affinity and specificity for animal steroid hormones have been demonstrated in fungi (30), algae (31), and plants (32). Moreover, the cellular machinery that is required to mediate steroid hormone action is evolutionary conserved across many eukaryotes (33)(34)(35)(36).…”

A New Method to Localize and Test the Significance of Incongruence: Detecting Domain Shuffling in the Nuclear Receptor Superfamily

“…Nuclear receptors have been identified but not fully sequenced in a wider range of taxa, including flatworms and cnidarians (Escriva et al, 1997). Steroids may regulate transcription in slime molds and some plants, but no nuclear receptors have been identified outside the metazoa (Brunt et al, 1990;Moore, 1990;Agarwal, 1993;Escriva et al, 1997). Nuclear receptors have been named on an ad hoc basis by their discoverers, usually on the basis of one aspect of their function or expression.…”