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Dong Lin

Bio: Dong Lin is an academic researcher from University of California, San Francisco. The author has contributed to research in topics: Pregnenolone & Cholesterol side-chain cleavage enzyme. The author has an hindex of 13, co-authored 17 publications receiving 2462 citations. Previous affiliations of Dong Lin include Albert Einstein College of Medicine & University of California.

Papers
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Journal ArticleDOI
24 Mar 1995-Science
TL;DR: In three unrelated individuals with this disorder, steroidogenic acute regulatory protein, which enhances the mitochondrial conversion of cholesterol into pregnenolone, was mutated and nonfunctional, providing genetic evidence that this protein is indispensable normal adrenal and gonadal steroidogenesis.
Abstract: Congenital lipoid adrenal hyperplasia is an autosomal recessive disorder that is characterized by impaired synthesis of all adrenal and gonadal steroid hormones In three unrelated individuals with this disorder, steroidogenic acute regulatory protein, which enhances the mitochondrial conversion of cholesterol into pregnenolone, was mutated and nonfunctional, providing genetic evidence that this protein is indispensable normal adrenal and gonadal steroidogenesis

976 citations

Journal ArticleDOI
TL;DR: Steroidogenic acute regulatory protein (StAR) appears to mediate the rapid increase in pregnenolone synthesis stimulated by tropic hormones and StAR mRNA levels are regulated by cAMP.
Abstract: Steroidogenic acute regulatory protein (StAR) appears to mediate the rapid increase in pregnenolone synthesis stimulated by tropic hormones. cDNAs encoding StAR were isolated from a human adrenal cortex library. Human StAR, coexpressed in COS-1 cells with cytochrome P450scc and adrenodoxin, increased pregnenolone synthesis > 4-fold. A major StAR transcript of 1.6 kb and less abundant transcripts of 4.4 and 7.5 kb were detected in ovary and testis. Kidney had a lower amount of the 1.6-kb message. StAR mRNA was not detected in other tissues including placenta. Treatment of granulosa cells with 8-bromo-adenosine 3',5'-cyclic monophosphate for 24 hr increased StAR mRNA 3-fold or more. The structural gene encoding StAR was mapped using somatic cell hybrid mapping panels to chromosome 8p. Fluorescence in situ hybridization placed the StAR locus in the region 8p11.2. A StAR pseudogene was mapped to chromosome 13. We conclude that StAR expression is restricted to tissues that carry out mitochondrial sterol oxidations subject to acute regulation by cAMP and that StAR mRNA levels are regulated by cAMP.

377 citations

Journal ArticleDOI
TL;DR: expression of StAR in COS-1 cells cotransfected with cholesterol 27-hydroxylase and adrenodoxin resulted in a 6-fold increase in formation of 3 beta-hydroxy-5-cholestenoic acid, demonstrating that StAR's actions are not specific to steroidogenesis but extend to other mitochondrial cholesterol-metabolizing enzymes.
Abstract: Steroidogenic acute regulatory protein (StAR) plays a key role in steroid hormone synthesis by enhancing the metabolism of cholesterol into pregnenolone. We determined the organization of the StAR structural gene, mapped to 8p11.2. The gene spans 8 kb and consists of seven exons interrupted by six introns. The 1.3 kb of DNA upstream from the transcription start site directed expression of a luciferase reporter gene in mouse Y-1 adrenal cortical tumor cells but not in BeWo choriocarcinoma cells. Reporter gene expression in the Y-1 cells was increased more than 2-fold by 8-Br-cAMP, indicating that the 1.3 kb DNA fragment contains sequences that confer tissue-specific expression and cAMP regulation. The sequence of a related StAR pseudogene, mapped to chromosome 13, lacks introns and has an insertion, numerous substitutions, and deletions. Expression of StAR in COS-1 cells cotransfected with cholesterol 27-hydroxylase (P450c27) and adrenodoxin resulted in a 6-fold increase in formation of 3 beta-hydroxy-5-cholestenoic acid, demonstrating that StAR's actions are not specific to steroidogenesis but extend to other mitochondrial cholesterol-metabolizing enzymes.

208 citations

Journal ArticleDOI
TL;DR: The data suggest that the essential role of Ser106 is in the active site, rather than in interacting with P450 reductase, and that electron transfer may play an important role in regulating the 17,20-lyase activity of P450c17.
Abstract: Cytochrome P450c17 (EC 1.14.99.9) catalyzes both 17 alpha-hydroxylase and 17,20-lyase activities in mammalian steroidogenesis and also has some 16 alpha-hydroxylase activity. The ratio of 17 alpha-hydroxylase to 17,20-lyase activity differs in the adrenal and testis and is developmentally regulated at adrenarche, but the nature of the enzyme's active site and the differential regulation of its two principal activities are unknown. The spontaneous human P450c17 mutation Ser106-->Pro eliminates all enzymatic activity. We used site-directed mutagenesis to construct expression vectors for the conservative P450c17 mutations Ser106-->Thr and Ser106-->Ala. When expressed in transfected COS-1 cells, these mutants retain only 20-30% of the 17 alpha-hydroxylase and 17,20-lyase activities, but retain 60% of the 16 alpha-hydroxylase activity of the Ser106 wild type. Thus, the amino acid occupying position 106 greatly affects enzymatic activity. Ser is found at position 106 in P450c17 in all mammals and birds studied, but the corresponding residue (position 112) in fish (trout) is Thr. Both the trout Thr112 wild type and a Thr112-->Ser trout mutant had equivalent 16 alpha-hydroxylase, 17 alpha-hydroxylase, and 17,20-lyase activities, although these were only 5%, 5%, and 10%, respectively, of human Ser106. To catalyze its activities, P450c17 must receive electrons from NADPH via a flavoprotein termed P450 reductase. We examined the influence of the ratio of P450c17 to P450 reductase on enzymatic activity by cotransfecting COS-1 cells with varying amounts of vectors expressing each protein. The endogenous P450 reductase of COS-1 cells was sufficient to confer maximal 17 alpha-hydroxylase activity. P450 reductase produced from the transfected expression vector did not increase the conversion of [14C]progesterone to 17 alpha- or 16 alpha-hydroxyprogesterone, indicating that the endogenous immunodetectable P450 reductase of COS-1 cells was sufficient to confer maximal 17 alpha-hydroxylase activity. By contrast, the additional P450 reductase produced by the expression vector increased 17,20-lyase activity about 3-fold. Thus, the availability of reducing equivalents is a crucial factor in regulating 17,20-lyase activity. P450 reductase also increased the 17,20-lyase activity of the Thr106 and Ala106 mutants. These data suggest that the essential role of Ser106 is in the active site, rather than in interacting with P450 reductase, and that electron transfer may play an important role in regulating the 17,20-lyase activity of P450c17.

166 citations

Journal ArticleDOI
TL;DR: This work uses site-directed mutagenesis of the normal P450c17 cDNA to construct the Pro106 mutant, and expressed both the normal and mutant sequences in monkey COS-1 cells and in yeast, proving that the Ser106----Pro mutation abolished the 17 alpha-hydroxylase and 17,20-lyase activities.

131 citations


Cited by
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TL;DR: The lability of sex-determination systems in fish makes some species sensitive to environmental pollutants capable of mimicking or disrupting sex hormone actions, and such observations provide important insight into potential impacts from endocrine disruptors, and can provide useful monitoring tools for impacts on aquatic environments.

2,283 citations

Journal ArticleDOI
TL;DR: The synthesis and excretion of bile acids comprise the major pathway of cholesterol catabolism in mammals and causes a spectrum of human disease; this ranges from liver failure in early childhood to progressive neuropathy in adults.
Abstract: ▪ Abstract The synthesis and excretion of bile acids comprise the major pathway of cholesterol catabolism in mammals. Synthesis provides a direct means of converting cholesterol, which is both hydrophobic and insoluble, into a water-soluble and readily excreted molecule, the bile acid. The biosynthetic steps that accomplish this transformation also confer detergent properties to the bile acid, which are exploited by the body to facilitate the secretion of cholesterol from the liver. This role in the elimination of cholesterol is counterbalanced by the ability of bile acids to solubilize dietary cholesterol and essential nutrients and to promote their delivery to the liver. The synthesis of a full complement of bile acids requires 17 enzymes. The expression of selected enzymes in the pathway is tightly regulated by nuclear hormone receptors and other transcription factors, which ensure a constant supply of bile acids in an ever changing metabolic environment. Inherited mutations that impair bile acid synth...

1,686 citations

Journal ArticleDOI
TL;DR: Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.
Abstract: Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

1,665 citations

Journal ArticleDOI
TL;DR: The likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear, is discussed.
Abstract: We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1–11, 1987; Nebert et al., DNA 8, 1–13, 1989; Nebert et al., DNA Cell Biol. 10, 1–14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating...

1,660 citations

Journal ArticleDOI
TL;DR: This review presents a detailed description of the enzymes involved in the biosynthesis of active steroid hormones, with emphasis on the human and mouse enzymes and their expression in gonads, adrenal glands, and placenta.
Abstract: Significant advances have taken place in our knowledge of the enzymes involved in steroid hormone biosynthesis since the last comprehensive review in 1988. Major developments include the cloning, identification, and characterization of multiple isoforms of 3β-hydroxysteroid dehydrogenase, which play a critical role in the biosynthesis of all steroid hormones and 17β-hydroxysteroid dehydrogenase where specific isoforms are essential for the final step in active steroid hormone biosynthesis. Advances have taken place in our understanding of the unique manner that determines tissue-specific expression of P450aromatase through the utilization of alternative promoters. In recent years, evidence has been obtained for the expression of steroidogenic enzymes in the nervous system and in cardiac tissue, indicating that these tissues may be involved in the biosynthesis of steroid hormones acting in an autocrine or paracrine manner. This review presents a detailed description of the enzymes involved in the biosynthe...

1,533 citations