Regulation of niemann-pick c1 gene expression by the 3'5'-cyclic adenosine monophosphate pathway in steroidogenic cells

NPC1 Confers Metabolic Flexibility in Triple Negative Breast Cancer

Triple-negative breast cancer (TNBC) often undergoes at least partial epithelial-to-mesenchymal transition (EMT) to facilitate metastasis. Identifying EMT-associated characteristics can reveal novel dependencies that may serve as therapeutic vulnerabilities in this aggressive breast cancer subtype. We found that NPC1, which encodes the lysosomal cholesterol transporter Niemann-Pick type C1 is highly expressed in TNBC as compared to estrogen receptor-positive (ER+) breast cancer, and is significantly elevated in high-grade disease. We demonstrated that NPC1 is directly targeted by microRNA-200c (miR-200c), a potent suppressor of EMT, providing a mechanism for its differential expression in breast cancer subtypes. The silencing of NPC1 in TNBC causes an accumulation of cholesterol-filled lysosomes, and drives decreased growth in soft agar and invasive capacity. Conversely, overexpression of NPC1 in an ER+ cell line increases invasion and growth in soft agar. We further identified TNBC cell lines as cholesterol auxotrophs, however, they do not solely depend on NPC1 for adequate cholesterol supply. The silencing of NPC1 in TNBC cell lines led to altered mitochondrial function and morphology, suppression of mTOR signaling, and accumulation of autophagosomes. A small molecule inhibitor of NPC1, U18666A, decreased TNBC proliferation and synergized with the chemotherapeutic drug, paclitaxel. This work suggests that NPC1 promotes aggressive characteristics in TNBC, and identifies NPC1 as a potential therapeutic target.

Transcript, protein, metabolite and cellular studies in skin fibroblasts demonstrate variable pathogenic impacts of NPC1 mutations

Background

Niemann-Pick type C (NP-C) is a rare neurovisceral genetic disorder caused by mutations in the NPC1 or the NPC2 gene. NPC1 is a multipass-transmembrane protein essential for egress of cholesterol from late endosomes/lysosomes. To evaluate impacts of NPC1 mutations, we examined fibroblast cultures from 26 NP-C1 patients with clinical phenotypes ranging from infantile to adult neurologic onset forms. The cells were tested with multiple assays including NPC1 mRNA expression levels and allele expression ratios, assessment of NPC1 promoter haplotypes, NPC1 protein levels, cellular cholesterol staining, localization of the mutant NPC1 proteins to lysosomes, and cholesterol/cholesteryl ester ratios. These results were correlated with phenotypes of the individual patients.

Results

Overall we identified 5 variant promoter haplotypes. Three of them showed reporter activity decreased down to 70% of the control sequence. None of the haplotypes were consistently associated with more severe clinical presentation of NP-C. Levels of transcripts carrying null NPC1 alleles were profoundly lower than levels of the missense variants. Low levels of the mutant NPC1 protein were identified in most samples. The protein localised to lysosomes in cultures expressing medium to normal NPC1 levels. Fibroblasts from patients with severe infantile phenotypes had higher cholesterol levels and higher cholesterol/cholesteryl ester ratios. On the contrary, cell lines from patients with juvenile and adolescent/adult phenotypes showed values comparable to controls.

Conclusion

No single assay fully correlated with the disease severity. However, low residual levels of NPC1 protein and high cholesterol/cholesteryl ester ratios associated with severe disease. The results suggest not only low NPC1 expression due to non-sense mediated decay or low mutant protein stability, but also dysfunction of the stable mutant NPC1 as contributors to the intracellular lipid transport defect.

The Orphan Nuclear Receptors Steroidogenic Factor-1 and Liver Receptor Homolog-1: Structure, Regulation, and Essential Roles in Mammalian Reproduction

Nuclear receptors are intracellular proteins that act as transcription factors. Proteins with classic nuclear receptor domain structure lacking identified signaling ligands are designated orphan nuclear receptors. Two of these, steroidogenic factor-1 (NR5A1, also known as SF-1) and liver receptor homolog-1 (NR5A2, also known as LRH-1), bind to the same DNA sequences, with different and nonoverlapping effects on targets. Endogenous regulation of both is achieved predominantly by cofactor interactions. SF-1 is expressed primarily in steroidogenic tissues, LRH-1 in tissues of endodermal origin and the gonads. Both receptors modulate cholesterol homeostasis, steroidogenesis, tissue-specific cell proliferation, and stem cell pluripotency. LRH-1 is essential for development beyond gastrulation and SF-1 for genesis of the adrenal, sexual differentiation, and Leydig cell function. Ovary-specific depletion of SF-1 disrupts follicle development, while LRH-1 depletion prevents ovulation, cumulus expansion, and luteinization. Uterine depletion of LRH-1 compromises decidualization and pregnancy. In humans, SF-1 is present in endometriotic tissue, where it regulates estrogen synthesis. SF-1 is underexpressed in ovarian cancer cells and overexpressed in Leydig cell tumors. In breast cancer cells, proliferation, migration and invasion, and chemotherapy resistance are regulated by LRH-1. In conclusion, the NR5A orphan nuclear receptors are nonredundant factors that are crucial regulators of a panoply of biological processes, across multiple reproductive tissues.

Overview of the Molecular Steps in Steroidogenesis of the GABAergic Neurosteroids Allopregnanolone and Pregnanolone

Allopregnanolone and pregnanolone-neurosteroids synthesized from progesterone in the brain, adrenal gland, ovary and testis-have been implicated in a range of neuropsychiatric conditions including seizure disorders, post-traumatic stress disorder, major depression, post-partum depression, pre-menstrual dysphoric disorder, chronic pain, Parkinson's disease, Alzheimer's disease, neurotrauma, and stroke. Allopregnanolone and pregnanolone equipotently facilitate the effects of gamma-amino-butyric acid (GABA) at GABAA receptors, and when sulfated, antagonize N-methyl-D-aspartate receptors. They play myriad roles in neurophysiological homeostasis and adaptation to stress while exerting anxiolytic, antidepressant, anti-nociceptive, anticonvulsant, anti-inflammatory, sleep promoting, memory stabilizing, neuroprotective, pro-myelinating, and neurogenic effects. Given that these neurosteroids are synthesized de novo on demand, this review details the molecular steps involved in the biochemical conversion of cholesterol to allopregnanolone and pregnanolone within steroidogenic cells. Although much is known about the early steps in neurosteroidogenesis, less is known about transcriptional, translational, and post-translational processes in allopregnanolone- and pregnanolone-specific synthesis. Further research to elucidate these mechanisms as well as to optimize the timing and dose of interventions aimed at altering the synthesis or levels of these neurosteroids is much needed. This should include the development of novel therapeutics for the many neuropsychiatric conditions to which dysregulation of these neurosteroids contributes.

Persistent Insulin Resistance in Podocytes Caused by Epigenetic Changes of SHP-1 in Diabetes

Poor glycemic control profoundly affects protein expression and the cell signaling action that contributes to glycemic memory and irreversible progression of diabetic nephropathy (DN). We demonstrate that SHP-1 is elevated in podocytes of diabetic mice, causing insulin unresponsiveness and DN. Thus, sustained SHP-1 expression caused by hyperglycemia despite systemic glucose normalization could contribute to the glycemic memory effect in DN. Microalbuminuria, glomerular filtration rate, mesangial cell expansion, and collagen type IV and transforming growth factor-β expression were significantly increased in diabetic Ins2^+/C96Y mice compared with nondiabetic Ins2^+/+ mice and remained elevated despite glucose normalization with insulin implants. A persistent increase of SHP-1 expression in podocytes despite normalization of systemic glucose levels was associated with sustained inhibition of the insulin signaling pathways. In cultured podocytes, high glucose levels increased mRNA, protein expression, and phosphatase activity of SHP-1, which remained elevated despite glucose concentration returning to normal, causing persistent insulin receptor-β inhibition. Histone posttranslational modification analysis showed that the promoter region of SHP-1 was enriched with H3K4me1 and H3K9/14ac in diabetic glomeruli and podocytes, which remained elevated despite glucose level normalization. Hyperglycemia induces SHP-1 promoter epigenetic modifications, causing its persistent expression and activity and leading to insulin resistance, podocyte dysfunction, and DN.

The promise and perils of HDAC inhibitors in neurodegeneration

Histone deacetylases (HDACs) represent emerging therapeutic targets in the context of neurodegeneration. Indeed, pharmacologic inhibition of HDACs activity in the nervous system has shown beneficial effects in several preclinical models of neurological disorders. However, the translation of such therapeutic approach to clinics has been only marginally successful, mainly due to our still limited knowledge about HDACs physiological role particularly in neurons. Here, we review the potential benefits along with the risks of targeting HDACs in light of what we currently know about HDAC activity in the brain.

Epigenetic regulation of cholesterol homeostasis

Although best known as a risk factor for cardiovascular disease, cholesterol is a vital component of all mammalian cells. In addition to key structural roles, cholesterol is a vital biochemical precursor for numerous biologically important compounds including oxysterols and bile acids, as well as acting as an activator of critical morphogenic systems (e.g., the Hedgehog system). A variety of sophisticated regulatory mechanisms interact to coordinate the overall level of cholesterol in cells, tissues and the entire organism. Accumulating evidence indicates that in additional to the more “traditional” regulatory schemes, cholesterol homeostasis is also under the control of epigenetic mechanisms such as histone acetylation and DNA methylation. The available evidence supporting a role for these mechanisms in the control of cholesterol synthesis, elimination, transport and storage are the focus of this review.

The stimulation of adenosine A2A receptors ameliorates the pathological phenotype of fibroblasts from Niemann-Pick type C patients

Niemann-Pick type C1 (NPC1) disease is a rare neurovisceral disorder characterized by intracellular accumulation of unesterified cholesterol, sphingolipids, and other lipids in the lysosomal compartment. A deregulation of lysosomal calcium has been identified as one of the earliest steps of the degenerative process. Since adenosine A2A receptors (A2ARs) control lysosome trafficking and pH, which closely regulates lysosomal calcium, we hypothesized a role for these receptors in NPC1. The aim of this study was to evaluate the effects of the A2AR agonist CGS21680 on human control and NPC1 fibroblasts. We show that CGS21680 raises lysosomal calcium levels and rescues mitochondrial functionality (mitochondrial inner membrane potential and expression of the complex IV of the mitochondrial respiratory chain), which is compromised in NPC1 cells. These effects are prevented by the selective blockade of A2ARs by the antagonist ZM241385. The effects of A2AR activation on lysosomal calcium are not mediated by the cAMP/PKA pathway but they appear to involve the phosphorylation of ERK1/2. Finally, CGS21680 reduces cholesterol accumulation (Filipin III staining), which is the main criterion currently used for identification of a compound or pathway that would be beneficial for NPC disease, and such an effect is prevented by the Ca(2+) chelator BAPTA-AM. Our findings strongly support the hypothesis that A2AR agonists may represent a therapeutic option for NPC1 and provide insights on their mechanisms of action.

Modulation of gene expression in ovarian cancer by active and repressive histone marks

DNA methylation and histone modifications often function concomitantly to drive an aberrant program of gene expression in most cancers. Consequently, they have also been identified as being associated with ovarian cancer. However, several basic issues remain unclear - are these marks established early during normal ovarian functioning, or at a preneoplastic stage, or through a gradual accumulation, or do they arise de novo during transformation? Such issues have been difficult to address in ovarian cancer wherein preneoplastic lesions and progression models have not yet been established and drug-refractive disease progression is rapid and aggressive. The review presents an overview of the known involvement of histone modifications in various cellular states that might contribute to our understanding of epithelial ovarian cancer.

Histone deacetylase inhibitor treatment dramatically reduces cholesterol accumulation in Niemann-Pick type C1 mutant human fibroblasts

Niemann-Pick type C (NPC) disease is predominantly caused by mutations in the NPC1 protein that affect intracellular cholesterol trafficking and cause accumulation of unesterified cholesterol and other lipids in lysosomal storage organelles. We report the use of a series of small molecule histone deacetylase (HDAC) inhibitors in tissue culture models of NPC human fibroblasts. Some HDAC inhibitors lead to a dramatic correction in the NPC phenotype in cells with either one or two copies of the NPC1(I1061T) mutation, and for several of the inhibitors, correction is associated with increased expression of NPC1 protein. Increased NPC1(I1061T) protein levels may partially account for the correction of the phenotype, because this mutant can promote cholesterol efflux if it is delivered to late endosomes and lysosomes. The HDAC inhibitor treatment is ineffective in an NPC2 mutant human fibroblast line. Analysis of the isoform selectivity of the compounds used implicates HDAC1 and/or HDAC2 as likely targets for the observed correction, although other HDACs may also play a role. LBH589 (panobinostat) is an orally available HDAC inhibitor that crosses the blood-brain barrier and is currently in phase III clinical trials for several types of cancer. It restores cholesterol homeostasis in cultured NPC1 mutant fibroblasts to almost normal levels within 72 h when used at 40 nM. The findings that HDAC inhibitors can correct cholesterol storage defects in human NPC1 mutant cells provide the potential basis for treatment options for NPC disease.

Molecular aspects of steroidogenic factor 1 (SF-1)

Steroidogenic factor 1 (SF-1, also called Ad4BP and NR5A1) is a nuclear receptor with critical roles in steroidogenic tissues, as well as in the brain and pituitary. In particular, SF-1 has emerged as an essential regulator of adrenal and gonadal functions and development. In the last few years, our knowledge on SF-1 has increased considerably at all levels, from the gene to the protein, and on its specific roles in different physiological processes. In this review, we discuss the current understanding on SF-1 with focus on the parameters that control the transcriptional capacity of SF-1 and the mechanisms that ensure proper stage- and tissue-specific expression of the gene encoding SF-1.

Developmental regulation of histone H3 methylation at lysine 4 in the porcine ovary

Follicular growth and oogenesis involve highly dynamic changes in morphogenesis, chromatin structure, and gene transcription. The tight coordination of these events leads to ovulation of a mature oocyte and formation of the luteal tissue necessary to regulate embryo implantation and development. This entire process is regulated by numerous endocrine and in situ mechanisms. The role of epigenetic mechanisms in folliculogenesis, such as the biochemical modification of the DNA packaging proteins, the histones, is not well understood. Our objective was to determine the cellular and follicular stage-specific patterns of histone H3 methylation at lysine 4 (K4) in porcine preovulatory follicles and during luteinization in pig ovaries. Ovary tissues were collected from slaughtered prepubertal and cyclic gilts at various stages of the estrous cycle, pregnancy, and from ovaries recovered from gonatropin-treated gilts at 0, 24, and 38 h post human chorionic gonadotropin (hCG) injection. Samples were fixed in 4% paraformaldehyde and processed for embedding in paraffin and sectioned using standard histological protocols. Immunofluorescent staining was performed on 3 microm thick sections. The immunostaining pattern of mono-, di-, and tri-methylated histone H3-K4 and lysine-specific demethylase 1 (LSD1, also known as KDM1 or AOF1) was assessed. Interestingly, H3-K4 mono-, di-, and tri-methylation in follicles of prepubertal gilts was specifically distributed and developmentally regulated. While granulosa cells of primary, secondary, and early antral follicles were negative for H3-K4 methylation those from large antral follicles showed a striking upregulation in the cells located in the proximity to the oocyte. Specifically, the cumulus oophorus displayed intense staining for H3-K4 methylation and signals were strongest in the granulosa cells in the inner two cell layers of the follicular wall. Although all oocytes from primary to large antral stage follicles were positive for H3-K4 mono-, di-, and tri-methylation, the patterns of distribution were altered through oocyte follicle development. H3-K4 methylation in granulosa cells was dramatically reduced as time to ovulation approached and was low to undetected at 38 h post hCG treatment. H3-K4 mono-, di-, and tri-methylation in large luteal cells increased as differentiation evolved but remained low in small luteal cells. Strikingly, LSD1 (KDM1) expression was found to be restricted to the corpus luteum. In summary, this study provides new information on histone H3-K4 methylation patterns in the oocyte and follicle during folliculogenesis, which suggests that these epigenetic markers serve an essential regulatory role during folliculogenesis.

cAMP-mediated regulation of cholesterol accumulation in cystic fibrosis and Niemann-Pick type C cells

The goal of this study was to identify a mechanism regulating cholesterol accumulation in cystic fibrosis (CF) cells. Both CFTR activation and expression are regulated by the cAMP pathway, and it is hypothesized that a feedback response involving this pathway may be involved in the phenotype of cholesterol accumulation. To examine the role of the cAMP pathway in cholesterol accumulation, we treated two CF model cell lines with the Rp diastereomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS) and visualized by filipin staining. Rp-cAMPS treatment eliminated cholesterol accumulation in CF cells, whereas 8-bromo-cAMP treatment led to cholesterol accumulation in wild-type cells. To confirm these findings in an independent model system, we also examined the role of cAMP in modulating cholesterol accumulation in Niemann-Pick type C (NPC) fibroblasts. Expression of the protein related to NPC, NPC1, is also directly regulated by cAMP; therefore, it is postulated that NPC cells exhibit the same cAMP-mediated control of cholesterol accumulation. Cholesterol accumulation in NPC cells also was reduced by the presence of Rp-cAMPS. Expression of beta-arrestin-2 (betaarr2), a marker of cellular response to cAMP signaling, was significantly elevated in CF model cells, Cftr(-/-) MNE, primary tissue obtained by nasal scrapes from CF subjects, and in NPC fibroblasts compared with respective controls.

Cholesterol supply and SREBPs modulate transcription of the Niemann-Pick C-1 gene in steroidogenic tissues

We tested whether sterol-regulatory element binding proteins (SREBPs) mediate sterol-regulated transactivation of the Niemann-Pick C-1 (NPC-1) gene. Loading granulosa cells with 22- or 25-hydroxycholesterol decreased NPC-1 mRNA, whereas culturing in cholesterol-depleted medium or inhibition of cholesterol biosynthesis increased NPC-1 promoter activity and NPC-1 mRNA abundance. Cotransfection of SREBP1a, SREBP1c, and SREBP2 and the NPC-1 promoter-luciferase reporter into granulosa cell lines increased the transcriptional activity of porcine, human, and mouse NPC-1 promoters. Deletion analysis of the 5' flanking region of the pig NPC-1 gene demonstrated significant promoter activity between fragments -934 and -636 bp upstream from the transcription initiation site. Sequence analysis revealed three sterol-regulatory elements (SREs) clustered between -558 and -650 bp. Each site, along with E-box sequences, bound recombinant SREBP in electromobility shift assays. Mutation of all three sites attenuated the SREBP induction of promoter activity. Chromatin immunoprecipitation (ChIP) assays revealed that cholesterol depletion enriched the association of both SREBP and acetylated histone H3 with the NPC-1 promoter fragment containing the three SREs. ChIP analysis confirmed that SREBP's association with SRE and the E-box was enriched in cells cultured in cholesterol-depleted medium. We conclude that NPC-1 is sterol-regulated, achieved by SREBP acting via SRE and the E-box sequences.

The Niemann-Pick C1 gene is downregulated by feedback inhibition of the SREBP pathway in human fibroblasts

The Niemann-Pick C1 (NPC1) protein regulates the transport of cholesterol from late endosomes/lysosomes to other compartments responsible for maintaining intracellular cholesterol homeostasis. The present study examined the expression of the NPC1 gene and the distribution of the NPC1 protein that resulted from the transport of LDL-derived cholesterol through normal human fibroblasts. A key finding was that the transport of cholesterol from late endosomes/lysosomes to the sterol-regulatory pool at the endoplasmic reticulum, as determined by feedback inhibition of the sterol-regulatory element binding protein (SREBP) pathway, was associated with the downregulation of the NPC1 gene. Consistent with these results, fibroblasts incubated with LDL had decreased amounts of SREBP protein that interacted with sterol-regulatory element (SRE) sequences positioned within the NPC1 gene promoter region. Finally, partial colocalization of the NPC1 protein with late endosomes/lysosomes and distinct regions of the endoplasmic reticulum suggested that the NPC1 protein may facilitate the transport of cholesterol directly between these two compartments. Together, these results indicate that the transport of LDL-derived cholesterol from late endosomes/lysosomes to the sterol-regulatory pool, known to be regulated by the NPC1 protein, is responsible for promoting feedback inhibition of the SREBP pathway and downregulation of the NPC1 gene.

p21 transcription is regulated by differential localization of histone H2A.Z

In yeast cells, H2A.Z regulates transcription and is globally associated within a few nucleosomes of the initiator regions of numerous promoters. H2A.Z is deposited at these loci by an ATP-dependent complex, Swr1.com. Here we show that H2A.Z suppresses the p53 --> p21 transcription and senescence responses. Upon DNA damage, H2A.Z is first evicted from the p21 promoter, followed by the recruitment of the Tip60 histone acetyltransferase to activate p21 transcription. p400, a human Swr1 homolog, is required for the localization of H2A.Z, and largely colocalizes with H2A.Z at multiple promoters investigated. Notably, the presence of sequence-specific transcription factors, such as p53 and Myc, provides positioning cues that direct the location of H2A.Z-containing nucleosomes within these promoters. Collectively, this study strongly suggests that certain sequence-specific transcription factors regulate transcription, in part, by preferentially positioning histone variant H2A.Z within chromatin. This H2A.Z-centered process is part of an epigenetic process for modulating gene expression.

The imitation switch protein SNF2L regulates steroidogenic acute regulatory protein expression during terminal differentiation of ovarian granulosa cells

Luteinization is a complex process, stimulated by gonadotropins, that promotes ovulation and development of the corpus luteum through terminal differentiation of granulosa cells. The pronounced expression of the mammalian imitation switch (ISWI) genes, SNF2H and SNF2L, in adult ovaries prompted us to investigate the role of these chromatin remodeling proteins during follicular development and luteinization. SNF2H expression is highest during growth of preovulatory follicles and becomes less prevalent during luteinization. In contrast, both SNF2L transcript and SNF2L protein levels are rapidly increased in granulosa cells of the mouse ovary 8 h after human chorionic gonadotropin treatment, and continue to be expressed 36 h later within the functional corpus luteum. We demonstrate a physical interaction between SNF2L and the progesterone receptor A isoform, which regulates progesterone receptor-responsive genes required for ovulation. Moreover, chromatin immunoprecipitation demonstrated that, after gonadotropin stimulation, SNF2L is associated with the proximal promoter of the steroidogenic acute regulatory protein (StAR) gene, a classic marker of luteinization in granulosa cells. Interaction of SNF2L with the StAR promoter is required for StAR expression, because small interfering RNA knockdown of SNF2L prevents the activation of the StAR gene. Our results provide the first indication that ISWI chromatin remodeling proteins are responsive to the LH surge and that this response is required for the activation of the StAR gene and the overall development of a functional luteal cell.

Estrogen Mediates Phosphorylation of Histone H3 in Ovarian Follicle and Mammary Epithelial Tumor Cells via the Mitotic Kinase, Aurora B

Cells of the ovarian follicle undergo extensive proliferation and differentiation from the time that the follicle escapes from the primordial state to its acquisition of ovulatory capacity. We examined the dynamic modification of the phosphorylation state of the histone H3 N-terminal tail in granulosa cells during follicular development. In rodent follicles, the granulosa cell H3 phosphorylation on Ser10 peaks during proestrus. This epigenetic mark is induced by both FSH and 17β-estradiol (E2), acting independently. E2-induced H3 phosphorylation fails to occur in mice with inactivated α-isoform of the nuclear estrogen receptor. E2 induction of histone phosphorylation is attenuated by cell cycle inhibition. Further, E2 induces the activity of the mitotic kinase, Aurora B, in a mammary tumor cell model where mitosis is estrogen receptor-α dependent. These results provide evidence for mitotic regulation in follicle development by estrogen and demonstrate a previously undiscovered mechanism for induction of cell proliferation in ovarian and mammary gland cells.

Epigenetic control of ovarian function: the emerging role of histone modifications

The dynamic nature of the ovarian follicle makes it an ideal model to study the coordinated activation and inactivation of genes related to cell growth and differentiation. Much progress has been made in identifying transcription factors that promote the transcription of ovarian genes mediating gonadotropin action and steroidogenesis, but how these factors promote transcription in the context of chromatin is not well understood. Over the past 5 years, epigenetic regulation of ovarian genes through histone modifications has been the focus of an increasing number of studies. Several coactivators and corepressors associated with transcription factors are in fact histone acetyltransferases and histone deacetylases mediating the hyperacetylation and hypoacetylation of histones, respectively. Hyperacetylation of lysine residues in the core histone tails promotes chromatin alterations that favor transcription, whereas hypoacetylation of histones promotes gene silencing or repression. Not only does the acetylation status of the core histones determine whether chromatin remodeling occurs, but histone phosphorylation and methylation may serve equally important roles. For example, the combination of histone H3 phosphorylation and acetylation concertedly favors transcription. In addition, specific lysine methylations (e.g., K9 of histone H3) repress gene expression whereas other methylations promote gene expression. It is most likely the combination of histone modification events that regulate the initiation of transcription. Understanding how ovarian hormones control specific histone modifications will help us understand how follicular cells can switch from active gene pools governing cell proliferation to those gene groups controlling terminal differentiation. Progress in elucidating the ovarian specific regulation of histone modifying enzymes as well as identification of their target gene pools at different stages of the follicular cycle is expected in the next few years.

Niemann-Pick C1 expression is not regulated by the amount of cholesterol flowing through cells in the mouse

The Niemann-Pick C1 (NPC1) protein functions to regulate the transport of cholesterol from late endosomes/lysosomes to other cellular compartments after lipoprotein uptake through the coated-pit pathway. The present study examines the relative expression of NPC1 mRNA and NPC1 protein in different tissues of the mouse in relation to the uptake of total cholesterol carried in chylomicron remnants (CMr-TC), low density lipoproteins (LDL-TC), cholesteryl ester carried in high density lipoproteins (HDL-CE), and cholesterol synthesis. Results from this study demonstrate that the highest relative expression of NPC1 is in the liver, which is also the tissue with the highest uptake of CMr-TC, LDL-TC, HDL-CE, and cholesterol synthesis. However, there was no similar relation in the remaining tissues. To examine the relative expression of NPC1 in relation to the amount of cholesterol that flowed through the coated-pit pathway, mice were fed a diet supplemented with increasing amounts of cholesterol or cholestyramine. The results from this study demonstrated that there was no relation between the relative expression of NPC1 and the amount of cholesterol that flowed through the coated-pit pathway. We conclude that the relative expression of NPC1 is not regulated by the flow of cholesterol through cells in the mouse and is therefore constitutive.

Adrenocortical cell lines

The human adrenal cortex is a complex endocrine organ that secretes mineralocorticoids, glucocorticoids and adrenal androgens. These steroids arise from morphologically and biochemically distinct zones of the adrenal gland. Studying secretion of these distinct steroid hormones can make use of cells isolated from the adrenal gland but this requires animal sacrifice and the need for continued isolation for long-term studies. In addition primary cultures of adrenal cells have a limited life-span in culture and the cultured cells are often contaminated by the presence of non-steroidogenic cells. For that reason in vitro cell culture models have several benefits for research on adrenocortical function. Herein we discuss the available adrenocortical cell lines and their uses as model systems for adrenal studies. Focus is placed on the human NCI-H295 and mouse Y-1 adrenal cell lines, which have been used extensively as adrenocortical model systems. These cell lines have proven to be of considerable value in studying the molecular and biochemical mechanisms controlling adrenal steroidogenesis. The current review will discuss the attributes and limitations of the currently available adrenocortical cell lines as models for adrenal studies.

Cholesterol transport and steroidogenesis by the corpus luteum

The synthesis of progesterone by the corpus luteum is essential for the establishment and maintenance of early pregnancy. Regulation of luteal steroidogenesis can be broken down into three major events; luteinization (i.e., conversion of an ovulatory follicle), luteal regression, and pregnancy induced luteal maintenance/rescue. While the factors that control these events and dictate the final steroid end products are widely varied among different species, the composition of the corpus luteum (luteinized thecal and granulosa cells) and the enzymes and proteins involved in the steroidogenic pathway are relatively similar among all species. The key factors involved in luteal steroidogenesis and several new exciting observations regarding regulation of luteal steroidogenic function are discussed in this review.