Cholesterol sulfotransferase of newborn mouse epidermis

Role of the liver X receptors in skin physiology: Putative pharmacological targets in human diseases

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that have been shown to regulate various physiological functions such as lipid metabolism and cholesterol homeostasis. Concordant reports have elicited the possibility to target them to cure many human diseases including arteriosclerosis, cancer, arthritis, and diabetes. The high relevance of modulating LXR activities to treat numerous skin diseases, mainly those with exacerbated inflammation processes, contrasts with the lack of approved therapeutic use. This review makes an assessment to sum up the findings regarding the physiological roles of LXRs in skin and help progress towards the therapeutic and safe management of their activities. It focuses on the possible pharmacological targeting of LXRs to cure or prevent selected skin diseases.

Regulation of sulfotransferase and UDP-glucuronosyltransferase gene expression by the PPARs

During phase II metabolism, a substrate is rendered more hydrophilic through the covalent attachment of an endogenous molecule. The cytosolic sulfotransferase (SULT) and UDP-glucuronosyltransferase (UGT) families of enzymes account for the majority of phase II metabolism in humans and animals. In general, phase II metabolism is considered to be a detoxication process, as sulfate and glucuronide conjugates are more amenable to excretion and elimination than are the parent substrates. However, certain products of phase II metabolism (e.g., unstable sulfate conjugates) are genotoxic. Members of the nuclear receptor superfamily are particularly important regulators of SULT and UGT gene transcription. In metabolically active tissues, increasing evidence supports a major role for lipid-sensing transcription factors, such as peroxisome proliferator-activated receptors (PPARs), in the regulation of rodent and human SULT and UGT gene expression. This review summarizes current information regarding the regulation of these two major classes of phase II metabolizing enzyme by PPARs.

LXR and PPAR activators stimulate cholesterol sulfotransferase type 2 isoform 1b in human keratinocytes

Liver X receptors (LXRs) and peroxisome proliferator-activated receptors (PPARs) are potent regulators of keratinocyte proliferation, differentiation, and epidermal permeability barrier homeostasis. Cholesterol sulfotransferase type 2B isoform 1b (SULT2B1b) is a key enzyme in the synthesis of cholesterol sulfate (CS), a critical regulator of keratinocyte differentiation and desquamation, as well as a mediator of barrier homeostasis. In this study, we assessed the effect of activators of LXR, PPARalpha, PPARbeta/delta, and PPARgamma on SULT2B1b gene expression and enzyme activity in cultured human keratinocytes (CHKs). Our results demonstrate that PPAR and LXR activators increase SULT2B1b mRNA levels, with the most dramatic effect (a 26-fold increase) induced by the PPARgamma activator ciglitazone. Ciglitazone upregulates SULT2B1b mRNA in a dose- and time-dependent manner. Moreover, the stimulation of SULT2B1b gene expression by LXR and PPAR activators occurs in both undifferentiated and differentiated CHKs. The upregulation of SULT2B1b mRNA by ciglitazone appears to occur at a transcriptional level, because the degradation of SULT2B1b is not accelerated by ciglitazone. In addition, cycloheximide almost completely blocks the ciglitazone-induced increase in SULT2B1b mRNA, suggesting that the transcription of SULTB1b mRNA is dependent on new protein synthesis. Finally, LXR and PPAR activators also increased the activity of cholesterol sulfotransferase. Thus, LXR and PPAR activators regulate the expression of SULT2B1b, the key enzyme in the synthesis of CS, which is a potent regulator of epidermal differentiation and corneocyte desquamation.

Steroid hormone synthesis in pregnancy

The goal of this article is to summarize what is known about the pathways of steroid hormone synthesis and metabolism in human pregnancy. Emphasis is placed on the distinctions between steroidogenic pathways in adults and those that are operative during human pregnancy.

Purification and characterization of cholesterol sulfotransferase from rat skin

Previous work has demonstrated that the activity of the enzyme cholesterol sulfotransferase is rapidly and dramatically increased upon squamous differentiation of a variety of epithelial cells in culture, including epidermal keratinocytes. As a step toward understanding the molecular mechanisms underlying this differentiation-related change, we now report the partial purification and characterization of this enzyme activity from rat skin. Supernatant solutions from rat skin homogenates were subjected to a series of column chromatography steps including anion exchange, gel filtration, chromatofocusing and hydrophobic interaction chromatography. The purification procedure resulted in cholesterol sulfotransferase activity purified 2700-fold with a 11% recovery. The most purified preparation yielded a major Coomassie blue-stained band on denaturing polyacrylamide gel electrophoresis of an apparent molecular weight (MW) of 40 000 Da. Photoaffinity labeling with the donor substrate, 3'-phosphoadenosine-5'-phospho-[35S]-sulfate resulted in a single radiolabeled protein band on denaturing polyacrylamide gel electrophoresis, again of apparent MW 40 000 Da, strongly suggesting that the major Coomassie blue-stained band in the most purified preparation is the cholesterol sulfotransferase protein. Among 3β-hydroxysteroids with a Δ5 double bond that were tested, each served as a substrate, while androgens, estrogens, corticosteroids, p-nitrophenol and DOPA did not serve as substrates. Apparent Michaelis constants for the 3β-hydroxysteroid substrates ranged from 0.6 to 8 µM.Key words: sulfotransferase, ichthyosis, cholesterol, skin, enzymology.

Alterations in cholesterol sulfate and its biosynthetic enzyme during multistage carcinogenesis in mouse skin

Recent evidence suggests that cholesterol sulfate may be an important second messenger involved in signaling epidermal differentiation in skin. The activity of cholesterol sulfotransferase (Ch-ST) is increased during squamous differentiation of keratinocytes and is believed to be a marker enzyme for terminal differentiation. The primary objective of this study was to examine changes in levels of cholesterol sulfate (CS) and activity of its biosynthetic enzyme, Ch-ST, during multistage carcinogenesis in mouse skin. Using SENCAR mice, we determined the activity of Ch-ST in normal epidermis, in tumor promoter-treated epidermis, in epidermis during wound healing, and in mouse skin tumors generated by initiation-promotion regimens. A single topical application of tumor promoters led to significantly elevated levels of Ch-ST activity and of CS. Epidermal Ch-ST activity was also elevated during wound healing. Dramatic increases in CS levels and in the activity of Ch-ST were found in nearly all of the papillomas and squamous cell carcinomas examined. The increased levels of CS and activity of Ch-ST in tumor promoter-treated epidermis were accompanied by increased transglutaminase-I activity. In contrast, transglutaminase I activity was not elevated in primary papillomas or squamous cell carcinomas. Finally, Ch-ST activity was significantly elevated in the epidermis of newborn HK1.ras transgenic mice, whereas transglutaminase I activity did not correlate with Ch-ST activity in these mice. These results demonstrate that diverse tumor-promoting stimuli all produce elevated CS levels and Ch-ST activity and that CS levels and Ch-ST activity were constitutively elevated in both papillomas and squamous cell carcinomas. The data also suggest a mechanism for upregulation of Ch-ST in skin tumors involving activation/upregulation of Ha-ras.

Epidermal steroid sulfatase and cholesterol sulfotransferase are regulated during late gestation in the fetal rat

Lipids in the stratum corneum (SC) are organized into lamellar membrane unit structures that provide the permeability barrier. Cholesterol sulfate, a SC membrane lipid, is synthesized by cholesterol sulfotransferase (CSTase) in the lower epidermis and hydrolyzed to cholesterol by steroid sulfatase (SSase) in the SC. To determine whether these enzymes are induced during barrier ontogenesis, we examined their activity in epidermis of fetal rats before (gestational day 17), during (day 19), and after (day 21) barrier formation. CSTase activity increased approximately 10-fold between day 17 and day 19, then declined between day 19 and day 21. In contrast, SSase activity reached its peak activity on day 21, increasing >5-fold. Fetal rat skin explants develop a SC and barrier over the same time course in vitro as in utero. Likewise, CSTase and SSase activities during in vitro ontogenesis precisely mirrored those obtained in utero. Moreover, hormones that accelerate barrier ontogenesis (e.g. glucocorticoids, thyroid hormone, and estrogen) accelerated the increase in CSTase and SSase activities during in vitro ontogenesis. mRNA levels of SSase increased in parallel with enzymatic activity, suggesting that these developmental changes are regulated at the genomic level. Finally, addition of exogenous cholesterol sulfate to explants in vitro did not accelerate either SC development or barrier formation. These studies suggest that induction of the cholesterol sulfate cycle enzymes during SC ontogenesis is a component of the fetal epidermal differentiation program and that the synthetic and degradative enzymes of this pathway are differentially regulated.

Distribution of cholesterol sulfate and its anabolic and catabolic enzymes in various rabbit tissues

Cholesterol sulfate (CS) recently has been shown to be involved in signal transduction pathway. To evaluate its functional significance, we determined the concentration of CS, and the specific activities of cholesterol sulfotransferase and CS sulfatase in various tissues of rabbit, and compared them with the concentration of sulfoglycolipids in rabbit tissues. CS was present in the epithelia and mucosa, but not in the tunica muscularis, of the digestive tract, trachea, uterine endometrium and uterine cervix. It was also present in lung, spleen, kidney, prostate, skin, hair, and nail at relatively high concentrations. Its concentration in the uterine endometrium was nine times higher in pseudopregnant rabbits than in nonpregnant rabbits because of activation of cholesterol sulfotransferase and inhibition of CS sulfatase in the pseudopregnant rabbits. Sulfoglycolipids were not detected in the uterine endometria of either non-pregnant- or pseudopregnant rabbits. However, sulfoglycolipids were detected at relatively high concentrations in the cerebrum, cerebellum, stomach, duodenum, jejunum, testis, and kidney of rabbits and thus the tissues in which both sulfolipids were detected were the gastrointestinal tract and kidney. In the digestive tract, the concentration of CS decreased in the order esophagus, stomach, duodenum, and jejunum, but that of sulfatide increased in the same order, indicating distribution of CS in the squamous epithelium. In addition, both CS and sulfatide were detected in the serum. On the other hand, CS sulfatase activity was detected in all tissues examined, even in hair, from which the enzyme was liberated by brief sonication, and its highest specific activity was detected in the liver. The specific activity of cholesterol sulfotransferase varied among the tissues examined and was found to be significantly high in the esophageal epithelium and the uterine endometrium of pseudopregnant rabbit, indicating involvement of cholesterol sulfation in the formation of epithelium.

Programmed expression of cholesterol sulfotransferase and transglutaminase during epidermal differentiation of murine skin development

To clarify the role of cholesterol sulfate (CS) in the process of epidermal differentiation in vivo, we investigated the concentration of CS and the specific activities of cholesterol sulfotransferase (CST), cholesterol sulfate sulfatase (CS sulfatase) and epidermal transglutaminase (ETG) in murine skin in the pre- and postnatal periods. In the skin at day 14 of gestation, CS was not detected with TLC and the specific activities of all the enzymes were low. However, concomitant with the formation of the multilayered structure of the epidermis (at day 16), the specific activities of CST steeply increased. Although the insoluble CS sulfatase in the microsomal fraction remained at a relatively constant level, the soluble CST in the cytosol fraction showed a 6-fold increase from day 14 to day 16, and the activity decreased continuously in the following period, reaching one forty-sixth of the maximum level at 4-months-old mice. Reflected by the increase in activity, CS was detected in fetal skin at day 15, and the concentration in epidermis significantly increased during the gestation period, reaching maximum level at day 17. Furthermore, the changes in the concentration of cholesterol sulfate were identical with those of N-(O-linoleoyl)-omega-hydroxy fatty acyl sphingosine and its glucosyl derivative in the epidermis. On the other hand, the specific activity of ETG increased after birth. Thus, the activation of CST and ETG was shown to occur separately in association with the formation of the multilayered structure and thickening of the stratum corneum, respectively.

Regulation of phenol sulfotransferase expression in cultured bovine bronchial epithelial cells by hydrocortisone

One conjugative pathway for the inactivation of endogenous and exogenous hydroxylated aromatic compounds is catalyzed by phenol (aryl) sulfotransferases (PSTs), which esterify phenolic acceptors with sulfate. The tracheobronchial epithelium is commonly exposed to phenolic drugs and pollutants, and metabolic sulfation and PST activity in this tissue have been previously demonstrated. To determine what factors may control PST expression, extracts of serum-free, growth factor-supplemented cultures of bovine bronchial epithelial cells were assayed for PST activity and PST antigen. The most significant finding was dose-dependent, apparent stimulated expression by hydrocortisone (EC50 = 4 nM, maximal stimulation at 20 nM). Time-course experiments, however, revealed progressive loss of PST in the absence of corticosteroid. After decay of extant PST in steroid-free medium, hydrocortisone reinduced the expression of PST three to fivefold. Western blots using mouse anti-bovine PST revealed corresponding increases in 32 kDa PST protein levels in response to hydrocortisone. Steady state kinetic analyses indicated apparent Km values of 1-3 microM for 2-naphthol regardless of culture conditions. These results suggest that detoxification of phenolic compounds by sulfation may be regulated by corticosteroids.

Biosynthesis of 3'-phosphoadenosine-5'-phosphosulfate (PAPS) in rat skin

A rapid and sensitive radiometric assay was developed for the measurement of 3'-phosphoadenosine-5'-phosphosulfate (PAPS) biosynthesis in rat skin extract. The formation of PAP35S from sodium 35sulfate and ATP was quantified by the transfer of the 35sulfate to minoxidil by rat liver minoxidil sulfotransferase (MST). The assay is sensitive enough for the detection of as little as 2 pmol of PAP35S. The PAPS-generating system showed a pH optimum of 8.6, with an apparent Km value of 1 mM for the ATP-Mg2+ complex and 68 microM for sodium 35sulfate. ATP and Mg2+, present individually or together in equimolar concentrations, were inhibitory above 8 mM. Excess (or free) ATP was a competitive inhibitor with respect to the ATP-Mg2+ complex; the apparent Ki measured was 0.32 mM. The specific activity of the PAPS-generating system, measured in rat skin cytosol was 0.15 nmol PAPS/min/mg protein. The importance of PAPS generation in detoxification and bioactivation of xenobiotics in skin is discussed.

Minoxidil Sulfotransferase, a Marker of Human Keratinocyte Differentiation

The sulfation of minoxidil is catalyzed by a sulfotransferase activity in a number of tissues including skin. To investigate further the nature of the minoxidil sulfotransferase activity in epithelial tissue and to compare this activity to that of cholesterol sulfotransferase, which has already been shown to be induced during the differentiation of epithelial cells, we cultured normal human epidermal keratinocytes in a keratinocyte growth medium for 4 d, after which the media were replaced with either the same growth media or media with increasing Ca++ concentrations. Cholesterol sulfotransferase, minoxidil sulfotransferase, and transglutaminase were determined during the differentiation of the cells in the three media. Time-activity curves that suggested two different sulfotransferase activities were induced during the differentiation process. U-77581, a competitive inhibitor of minoxidil sulfotransferase activity, inhibited the sulfation of minoxidil sulfotransferase activity in the keratinocyte homogenates, but it did not inhibit the sulfation of cholesterol. These data indicate that at least two sulfotransferase activities are induced during the differentiation of epithelial keratinocytes and minoxidil sulfotransferase is an early marker of that differentiation.

Action of phorbol esters, bryostatins, and retinoic acid on cholesterol sulfate synthesis: relation to the multistep process of differentiation in human epidermal keratinocytes

This study examines the action of phorbol 12-myristate 13-acetate (PMA) on the synthesis of cholesterol sulfate in cultured normal and transformed human epidermal keratinocytes and assesses the antagonistic effects by retinoids and bryostatins on PMA action in relation to the multistep program of squamous differentiation. Treatment of normal human epidermal keratinocytes (NHEK) with PMA induces terminal cell division (irreversible growth-arrest) and causes a time- and dose-dependent increase in the incorporation of Na2(35)SO4 into cholesterol sulfate, a marker for squamous cell differentiation. This stimulation in sulfate incorporation appears specific for cholesterol sulfate and is due to increased levels of cholesterol sulfotransferase activity. The increase in cholesterol sulfate accumulation parallels the increase in transglutaminase type I, another marker for squamous differentiation. Several transformed NHEK cell lines do not exhibit increased levels of cholesterol sulfate and transglutaminase type I activity after PMA treatment, indicating that they acquired defects in the regulation of squamous differentiation. Bryostatins 1 and 2, and several diacylglycerol analogues neither inhibit cell proliferation nor increase cholesterol sulfate synthesis or transglutaminase activity, indicating that these agents do not induce terminal differentiation. In contrast, the bryostatins block the increase in cholesterol sulfate and transglutaminase activity as well as the commitment to terminal cell division by PMA. Bryostatin 1 inhibits the commitment to terminal cell division and the accumulation of cholesterol sulfate significantly even when added 8 h after PMA administration. Retinoids inhibit cholesterol sulfate accumulation and the increase in transglutaminase activity by PMA but do not affect the commitment to terminal cell division. In summary, phorbol esters induce in NHEK cells a program of squamous differentiation. This process of differentiation consists of the commitment to terminal cell division and expression of a squamous phenotype. Expression of this phenotype is accompanied by an accumulation of cholesterol sulfate and increased cholesterol sulfotransferase activity. Bryostatins 1 and 2 and retinoic acid affect this differentiation process at different stages.

Increased cholesterol sulfate and cholesterol sulfotransferase activity in relation to the multi-step process of differentiation in human epidermal keratinocytes

In this study the synthesis of cholesterol sulfate is examined in relation to the process of squamous differentiation in normal human epidermal keratinocytes (NHEK) in culture. During the exponential growth phase, NHEK cells exhibit a relatively high colony-forming efficiency and appear undifferentiated on the basis of their morphology and expression of biochemical characteristics. At confluence, the cells undergo terminal differentiation that is characterized by the commitment to terminal cell division (reduction in colony-forming ability) and expression of the differentiated phenotype. An accumulation of cholesterol sulfate accompanies this program of differentiation. This accumulation of cholesterol sulfate parallels the increase in transglutaminase type I activity and the competence to form cross-linked envelopes, whereas it precedes the "spontaneous" formation of cross-linked envelopes. Increased cholesterol sulfotransferase activity appears to account for the increase in cholesterol sulfate. The cholesterol sulfate accumulation, as well as the increase in cholesterol sulfotransferase and transglutaminase activity, are inhibited by retinoids. However, the presence of retinoids does not prevent NHEK cells from undergoing terminal cell division at confluence. Two NHEK cell lines expressing SV40-large T antigen also undergo terminal differentiation at confluence and start to accumulate cholesterol sulfate. Two other, differentiation-defective cell lines do not exhibit an increase in cholesterol sulfate at confluence. These results show that epidermal keratinocytes in culture, like cells in the epidermis, accumulate cholesterol sulfate when undergoing squamous differentiation. This program appears to consist of a retinoid-insensitive step (commitment to terminal cell division) and a retinoid-sensitive step (expression of the squamous differentiated phenotype).

Cholesterol sulfate uptake and outflux in cultured human keratinocytes

Cholesterol sulfate-cholesterol homeostasis in the epidermis may be important for normal desquamation. Recent evidence from cell-culture studies indicates that cholesterol sulfate inhibits sterologenesis by inhibiting the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, the rate-limiting enzyme in cholesterol synthesis. For cholesterol sulfate in the stratum corneum to function as a feedback regulator of epidermal sterologenesis, it must have the capacity enter cells. In these studies, uptake and outflux of cholesterol sulfate was examined in cultured human foreskin keratinocytes, and compared with uptake and outflux of cholesterol and 25-hydroxycholesterol, as well as with sterol uptake by another cell type, the skin fibroblast. The uptake of the free (not lipoprotein-associated) form of all three sterols was not consistent with a receptor-mediated process. Although the cholesterol sulfate uptake was approximately three-fold less than that of 25-hydroxycholesterol, it was nearly seven-fold greater than that of cholesterol itself. Whereas 25-hydroxycholesterol was rapidly washed out of keratinocytes in outflux experiments, both cholesterol and cholesterol sulfate tended to remain cell-associated. These studies demonstrate that cholesterol sulfate is readily taken up by keratinocytes, in which it may be in a position to modulate cellular lipid metabolism.