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Ilpo T Huhtaniemi

Publications and source records attributed to Ilpo T Huhtaniemi.

At least 19 recordsLinked to original sources
PubMed2007

GATA transcription factors in adrenal development and tumors.

Of the six GATA transcription factors, GATA-4 and GATA-6 are expressed in the mouse and human adrenal with distinct developmental profiles. GATA-4 is confined to the fetal cortex, i.e. to the less differentiated proliferating cells, while GATA-6 is expressed both in the fetal and adult adrenal. In vitro, GATA-4 regulates inhibin-alpha and steroidogenic factor-1 implicated in normal adrenal function. GATA-6 probably has roles in the development and differentiation of adrenocortical cells, and in the regulation of steroidogenesis. GATA-4 expression is dramatically upregulated and GATA-6 downregulated in gonadotropin dependent mouse adrenocortical tumors. This is accompanied by the appearance of luteinizing hormone receptor (LHR). In vitro, GATA-4 transactivates LHR promoter, and gonadotropins upregulate GATA-4 levels. Human adrenal tumors occasionally express GATA-4, whereas GATA-6 levels are usually lower than normal.

Adrenal Cortex Neoplasms↗
PubMed2006

Determination of androgen bioactivity in human serum samples using a recombinant cell based in vitro bioassay.

The present study describes the development and optimization of a cell-based reporter assay for the determination of androgen bioactivity levels in human serum samples. Towards this end, human embryonic kidney (HEK) 293 cells were cotransfected with two plasmids, one encoding the mouse mammary tumor virus (MMTV)-driven luciferase reporter gene and the other the SV40 promoter-driven human androgen receptor (AR), and a stable cell line, expressing human AR and androgen-responsive luciferase was established by antibiotic selection. RT-PCR confirmed proper transcription and stable integration of AR in the cell line. On stimulation of the cells with testosterone (T) for 24h, luciferase activity was increased in dose-dependent fashion up to 15-fold, with the minimum effective concentration of T being 0.03 nmol/l. T-induced reporter gene expression of the cells was inhibited by the anti-androgens cyproterone acetate and hydroxyflutamide. Upon stimulation with non-androgenic steroids like estradiol, progesterone, dexamethasone and cortisol, the cells showed only marginal activity except for a weak glucocorticoid effect at high concentration. The cells also responded well to various chemicals (mostly pesticides, their metabolites and common industrial chemicals) with known androgenic activity. The cell line was further optimized by measuring the levels of androgens from male and female serum samples. Our data indicated that the cells can be used to estimate androgen bioactivity in serum of females suffering from polycystic ovary syndrome (PCOS) and males of different age groups. In conclusion, we demonstrate that the bioassay based on this cell line provides a reliable method to determine serum levels of androgen bioactivity from biological samples even at the low concentrations present in female circulation. The 96-well plate format makes the assay suitable for high throughput measurements.

Androgens↗
PubMed2006

Differential endocrine regulation of genes enriched in initial segment and distal caput of the mouse epididymis as revealed by genome-wide expression profiling.

We have performed genome-wide expression profiling of endocrine regulation of genes expressed in the mouse initial segment (IS) and distal caput of the epididymis by using Affymetrix microarrays. The data revealed that of the 15 020 genes expressed in the epididymis, 35% were enriched in one of the two regions studied, indicating that differential functions can be attributed to the IS and the more distal caput regions. The data, furthermore, showed that 27% of the genes expressed in the IS and/or distal caput epididymidis are under the regulation of testicular factors present in the duct fluid, while bloodborne androgens can regulate for 14% of them. This is in line with the high testis dependency of epididymal physiology. We then focused on genes with moderate or strong expression, showing strict segment enrichment and strong dependency on testicular factors. Analyses of the 59 genes, including upregulated and downregulated genes, fulfilling the criteria indicated that the expression of 18 (17 downregulated genes; 1 upregulated gene) of 19 gonadectomy-responsive genes enriched in the IS was not maintained by the androgen treatment, whereas the expression of all six downregulated genes enriched in the distal caput and the majority of those with no strict segment enrichment of expression (28 of 34; consisting of 23 downregulated and 5 upregulated genes) were maintained by androgens. Hence, it is evident that testicular factors other than androgens are important for the expression of IS-enriched genes, whereas the expression of distal caput-enriched genes is typically regulated by androgens. Identical data were obtained by independent clustering analyses performed for the expression data of 3626 epididymal genes. Several novel genes with putative involvement in epididymal sperm maturation, such as a disintegrin and metallopeptidase domain 28 (Adam28) and a solute carrier organic anion transporter family, member 4C1 (Slco4c1), were identified, indicating that this approach is successful for identifying novel epididymal genes.

ADAM Proteins↗
PubMed2005

Fetal but not adult Leydig cells are susceptible to adenoma formation in response to persistently high hCG level: a study on hCG overexpressing transgenic mice.

We have previously demonstrated that male transgenic (TG) mice overexpressing human chorionic gonadotropin (hCG+) develop reproductive organ defects, but no tumors, in adult age. In this study, the effects of persistently elevated hCG were followed in TG males between day 5 postpartum and adulthood. Leydig cell (LC) adenomas were found in prepubertal mice, most prominently at the age of 10 days, but not in adult age. Serum testosterone concentrations were significantly increased in TG males at all ages studied. The phenotype of the prepubertal hCG+ males resembled that found in boys upon expression of constitutively activating luteinizing hormone (LH) receptor mutations. The temporal expression patterns of the fetal LC marker gene, thrombospondin 2, and those of adult LCs, hydroxysteroid dehydrogenase-6, delta5-3-beta and prostaglandin D synthase, were similar in wild-type and hCG+ males. Hence, the postnatal adenomas resemble functionally fetal LCs, and only these cells are susceptible to hCG-induced tumorigenesis. Our findings demonstrate a novel intriguing difference between the fetal and adult LC populations and provide further insight into the potential tumorigenic effects of gonadotropins.

3-Hydroxysteroid Dehydrogenases↗
PubMed2005

Molecular mechanisms of insulin-like growth factor-I mediated regulation of the steroidogenic acute regulatory protein in mouse leydig cells.

Growth factors are known to play diverse roles in steroidogenesis, a process regulated by the mitochondrial steroidogenic acute regulatory (StAR) protein. The mechanism of action of one such growth factor, IGF-I, was investigated in mouse Leydig tumor (mLTC-1) cells to determine its potential role in the regulation of StAR expression. mLTC-1 cells treated with IGF-I demonstrated temporal and concentration-dependent increases in StAR expression and steroid synthesis. However, IGF-I had no effect on cytochrome P450 side-chain cleavage or 3beta-hydroxysteroid dehydrogenase protein levels. IGF-I was capable of augmenting N,O'-dibutyrl-cAMP-stimulated steroidogenic responsiveness in these cells. The steroidogenic potential of IGF-I was also confirmed in primary cultures of isolated mouse Leydig cells. IGF-I increased phosphorylation of ERK1/2, an event inhibited by the MAPK/ERK inhibitors, PD98059 and U0126. Interestingly, inhibition of ERK activity enhanced IGF-I-mediated StAR protein expression, but phosphorylation of StAR was undetectable, an observation in contrast to that seen with N,O'-dibutyrl-cAMP signaling. Further studies demonstrated that these events were tightly correlated with the expression of dosage-sensitive sex reversal, adrenal hypoplasia congenita, critical region on the X chromosome, gene 1 and scavenger receptor class B type 1. Whereas both protein kinase A and protein kinase C signaling were involved in the IGF-I-mediated steroidogenic response, the majority of the effects of IGF-I were found to be mediated by the protein kinase C pathway. Transcriptional activation of the StAR gene by IGF-I was influenced by several transcription factors, its up-regulation being dependent on phosphorylation of the cAMP response element-binding protein (CREB) and the activator protein 1 family member, c-Jun. Conversely, StAR gene transcription was markedly inhibited by expression of nonphosphorylatable CREB (Ser(133)Ala), dominant negative A-CREB, and dominant negative c-Jun (TAM-67) mutants. Collectively, the present studies identify molecular events in IGF-I signaling that may influence testicular growth, development, and the Leydig cell steroidogenic machinery through autocrine/paracrine regulation.

3-Hydroxysteroid Dehydrogenases↗
PubMed2004

Testicular cell lines.

The range of in vivo or in vitro immortalized cell lines currently available provides a variety of model systems for studies of normal and pathological cell functions. The cell lines have been derived from spontaneous or experimentally induced tumors, or through in vitro immortalization. The transgenic (TG) techniques provide a powerful approach, allowing the production of in vivo animal models for a variety of diseases, including malignant tumors, through tissue-specific expression of oncogenes or other tumor-promoting genes. The TG techniques also enable the production of cell lines with specific characteristics, through insertion of desired genes into specific cell types, which can then be immortalized upon cell culture. The use of temperature-sensitive immortalizing genes offers an additional advantage of controlling gene expression, including the proliferation and differentiation of the cells to be immortalized. As regards the male reproductive system, a number of cell lines of testicular somatic cells are currently available. This review covers mainly the immortalized cell lines of testicular Leydig and Sertoli cells, with special reference to murine cell lines for the study of testicular endocrine function and tumorigenesis. These cell lines also provide useful tools to investigate the molecular basis of hormone actions and testicular cell interactions.

Animals↗
PubMed2004

Screening of some anti-androgenic endocrine disruptors using a recombinant cell-based in vitro bioassay.

The present work describes the development and optimization of a cell-based androgen reporter assay using the Chinese hamster ovarian cell line (CHO K1) in the 96-well format. The recent reports on increasing exposure of humans and wild-life to environmental endocrine disrupting chemicals (ED) prompt the need for high throughput screening systems for such compounds in environmental and biological samples. To this end, CHO cells were cotransfected with plasmids encoding mouse mammary tumour virus-neomycin-luciferase and human androgen receptor (hAR), and a stable cell line was established. After selection with neomycin, a highly active clone was obtained which stably expressed both the hAR and the androgen-responsive luciferase reporter. Stimulation of the cells with androgens for 24 h resulted in about 15-fold stimulation of luciferase activity, with the minimum effective dose of testosterone being 0.1 nmol/l. Potent steroidal and non-steroidal anti-androgens, such as hydroxyflutamide and cyproterone acetate, significantly inhibited the androgen-induced transactivation. Non-androgenic steroids like estradiol, progesterone, dexamethasone and cortisol showed weak activity at high concentrations. RT-PCR and western blot confirmed proper transcription and translation as well as stable expression of the AR gene in the cells. About 60 different chemicals (mostly pesticides or their metabolites, and common industrial chemicals) were screened with the cell line for their ability to stimulate luciferase activity or inhibit that evoked by 0.1 nmol/l R1881, used as a positive androgenic control. About 10 highly potent anti-androgenic chemicals were identified. The most potent anti-androgenic compounds identified in our assay included bisphenol A, alpha-hexachlorocyclohexane, vinclozolin and 4,4-DDE. These compounds had alone either no effect or were weak agonists (with cytotoxic effects at very high concentrations), but none showed any significant agonistic activity. In conclusion, we demonstrate that the bioassay based on this cell line provides a reliable test for detecting androgenic and anti-androgenic compounds. The 96-well plate format makes the assay suitable for high throughput screening.

Androgen Antagonists↗
PubMed2003

Immortalization of epididymal epithelium in transgenic mice expressing simian virus 40 T antigen: characterization of cell lines and regulation of the polyoma enhancer activator 3.

In the present study epididymal epithelium was immortalized in transgenic mice by expressing simian virus 40 T antigen under a 5.0-kb mouse glutathione peroxidase 5 promoter (GPX5-Tag1). Epididymal tumorigenesis was associated with an increase in c-Myc expression, and a marked decrease in B-Myc expression, with a 500-fold lower level in the GPX5-Tag1 caput epididymis compared with wild-type caput. Furthermore, B-Myc was undetectable in the immortalized corpus and cauda epididymis. Hence, it is possible that the normally high B-Myc expression in the epididymis is one of the factors contributing to the highly resistant nature of epididymis toward immortalization. Morphologically different epithelial cell lines were generated from the immortalized epididymides, and the cells expressed several genes typical for epididymal epithelium, such as mouse epididymal 1, mouse epididymal protein 9, androgen and estrogen receptors, anion exchangers 2 and 4, retinoic acid receptor alpha, and polyoma enhancer activator 3 (PEA3). This indicated the differentiated status of the cells and their usefulness for analyzing epididymal gene expression in vitro. As PEA3 is considered to be one of the transcription factors responsible for epididymal gene expression, we further studied its regulation in epididymal cells in vitro. The data showed that PEA3 mRNA expression is regulated in the epididymis via protein kinase A and ERK signaling cascades. Inhibiting protein kinase A resulted in up-regulation and inhibiting ERK resulted in down-regulation of PEA3 mRNA, whereas no significant effect on PEA3 expression was found by modulating the protein kinase C, stress-activated p38, phosphoinositol 3-kinase and p70 S6 kinase cascades.

Androgens↗
PubMed2003

Female mice carrying a ubiquitin promoter-Insl3 transgene have descended ovaries and inguinal hernias but normal fertility.

Mouse knockout studies have indicated that Insl3 is involved in development of the gubernaculum in males, which is essential for normal testicular descent. To determine further the functions of Insl3 we have generated transgenic (TG) mice ubiquitously expressing Insl3. In these mice low levels of transgenic Insl3 mRNA are expressed in all tissues analyzed. In the TG females the ovaries descend to the base of the abdominal cavity during the fetal period, as a consequence of the formation of male-like gubernaculum structures. Furthermore, the gubernacular structures developed express androgen receptor, identically to the corresponding structures in males. At adult age the ligaments formed connect the uterine horns to the inguinal region of the abdomen. Ligaments are also formed between the lower and upper parts of the uterine horns, and these ligaments force the uterus to form a coiled structure. However, the TG females retain their reproductive functions, indicating that neither the location of the ovaries nor the macroscopic structure of the uterus is vital for reproduction. In addition, Insl3 expression causes inguinal hernia in females, suggesting that a combination of estrogen and Insl3 action disrupts proper development of the muscular and connective tissue structures of the abdomen. The lack of a phenotype in other tissues indicates that gubernaculum formation is the most sensitive biological response as regards Insl3.

Animals↗
PubMed2003

Obesity in transgenic female mice with constitutively elevated luteinizing hormone secretion.

Transgenic (TG) female mice, expressing a chimeric bovine luteinizing hormone (LH) beta-subunit/human chorionic gonadotropin beta-subunit COOH-terminal extension (bLHbeta-CTP) gene, produce high levels of circulating LH and serve as a model for functional ovarian hyperandrogenism and follicular cysts. We report here that obesity is a typical feature of these female mice. The mean body weight of the bLHbeta-CTP females was significantly higher than in controls at, and beyond 5 wk of age, and at 5 mo, it was 32% increased. At this age, the amount of white adipose tissue in the bLHbeta-CTP females was significantly increased, as reflected by the weight difference of the retroperitoneal fat pad. In addition, the expression of leptin mRNA in white adipose tissue of the TG females was elevated about twofold. Serum leptin and insulin levels, and food intake, were also increased significantly in the TG females. Brown adipose tissue (BAT) thermogenic activity, as measured by GDP binding to BAT mitochondria, was reduced (P < 0.05). Ovariectomy at the age of 3 wk totally prevented the development of obesity. In summary, the present results show that intact female bLHbeta-CTP mice are obese, have increased food consumption, and reduced BAT thermogenic activity. The weight gain can be explained partly by elevated androgens but is probably also contributed to the increased adrenal steroidogenesis. Hence, the bLHbeta-CTP mice provide a useful model for studying obesity related to elevated LH secretion, with consequent alterations in ovarian and adrenal function.

Animals↗
PubMed2003

Gonadal morphology and sex hormones in male and female Wistar rats after long-term lamotrigine treatment.

Drug-induced disturbances in reproductive hormones and gonadal morphology have been observed both in patients with epilepsy and in non-epileptic animals. Less is known about the influence of newer antiepileptic drugs including lamotrigine on reproduction. Lamotrigine is now increasingly used both in epilepsy and psychiatric disorders. Sixty-five Wistar rats were fed by gastric tube either 5 mg kg(-1) lamotrigine solution (males=15, females=20) or 0 (vehicle control, males=15, females=15) twice daily for 90 days. In males, no significant differences were found in body or testicular weight. Testicular atrophy was observed in one control animal and in two of the rats receiving lamotrigine. No morphological changes were seen in the other organs investigated (liver, kidney, pancreas, brain, lymphatic tissue, heart). None of the animals showed over-expression of p53. No significant differences were observed between the control rats and the male rats receiving lamotrigine regarding testosterone, FSH and LH. In females, no changes in ovarian morphology or alterations in other tissues were observed. Serum testosterone, FSH, LH, insulin and progesterone remained unchanged in the lamotrigine treated animals, while serum estrogen was significantly reduced.

Animals↗
PubMed2003

A novel loss of function mutation in exon 10 of the FSH receptor gene causing hypergonadotrophic hypogonadism: clinical and molecular characteristics.

BACKGROUND: Inactivating mutations of the FSH receptor (FSHR) are a rare cause of hypergonadotrophic hypogonadism in women. Only one patient with primary amenorrhoea due to an FSHR gene mutation has been reported outside of Finland, where the prevalence of Ala189Val mutations is particularly high. METHODS AND RESULTS: Here, we describe the clinical, molecular genetic and functional characteristics associated with a novel inactivating mutation in exon 10 of the FSHR gene identified in a patient who presented with primary amenorrhoea at 17 years of age. The C to G transversion found at nucleotide 1043 causes a Pro348Arg substitution in the extracellular region of the FSHR and results in a mutant FSHR that is completely inactive in functional studies and that does not bind FSH. The proband exhibits apparent homozygosity for this recessive mutation. Her father is heterozygous for the mutation while analysis of exon 10 of the FSHR gene from her mother revealed only wild-type sequence. Chromosome painting was used to exclude deletions or rearrangements of 2p, and microsatellite markers did not show paternal uniparental isodisomy for this region. These findings suggest that the proband is hemizygous, with an inherited or de-novo microdeletion, or alternatively a de-novo gene conversion, of the accompanying FSHR allele. CONCLUSIONS: This case confirms the importance of the FSHR in female pubertal development and reproduction, and supports a relationship between phenotype and function for FSHR mutations.

Adolescent↗
PubMed2003

Failure of normal Leydig cell development in follicle-stimulating hormone (FSH) receptor-deficient mice, but not FSHbeta-deficient mice: role for constitutive FSH receptor activity.

Previous studies have suggested that FSH may be involved in regulation of Leydig cell function. We have examined this directly using two mouse models with null mutations in either the FSH beta-subunit (FSHbetaKO mice) or the FSH receptor (FSHRKO mice). Circulating LH levels were normal in adult FSHbetaKO mice, but were significantly increased in FSHRKO mice. Intratesticular testosterone levels increased normally in FSHbetaKO mice from birth to adulthood, whereas testosterone levels in FSHRKO mice failed to increase normally after puberty and were significantly reduced in adult animals. This was associated with reduced levels of mRNA encoding cytochrome P450 side-chain cleavage, 3beta-hydroxysteroid dehydrogenase type VI, and steroidogenic acute regulatory protein in FSHRKO mice. Leydig cell number was normal in FSHbetaKO mice during development, but in FSHRKO mice Leydig cell number increased slowly after puberty and was significantly reduced in the adult animal. Transfection studies showed that the FSHR exhibits constitutive activity in the absence of agonist stimulation. The results indicate, therefore, that Sertoli cells regulate the development of Leydig cell number and that constitutive activity within the FSHR is sufficient to stimulate this process. The presence of the hormone itself is not required when circulating LH levels are adequate.

Animals↗
PubMed2003

Mouse strain susceptibility to gonadectomy-induced adrenocortical tumor formation correlates with the expression of GATA-4 and luteinizing hormone receptor.

Certain inbred strains of mice, including DBA/2J, develop adrenocortical tumors in response to gonadectomy. Spindle-shaped cells with limited steroidogenic capacity, termed A cells, appear in the subcapsular region of the adrenal gland, followed by sex steroid-producing cells known as B cells. These changes result from unopposed gonadotropin production by the pituitary, but the adrenocortical factors involved in tumorigenesis have not been characterized. GATA-4, a transcription factor normally expressed in fetal, but not adult, adrenocortical cells, was found in neoplastic cells that proliferate in the adrenal cortex of gonadectomized DBA/2J mice. GATA-4 mRNA was detected in the adrenal glands of female mice 0.5 months after ovariectomy and reached a maximum by 4 months. Castrated male mice developed adrenocortical tumors more slowly than gonadectomized females, and the onset of GATA-4 expression in the adrenal was delayed. In situ hybridization and immunohistochemistry revealed GATA-4 mRNA and protein in A and B cells, but not in normal adrenocortical cells. mRNA encoding another factor associated with adrenocortical tumorigenesis, LH receptor (LHR), was detected in A and B cells. In addition, transcripts for P450 17 alpha-hydroxylase/C17-C20 lyase, an enzyme essential for the production of sex steroids, and inhibin-alpha were found in B cells. Unilateral ovarian regeneration, a phenomenon known to occur in gonadectomized mice, was observed in a subset of DBA/2J mice undergoing complete ovariectomy. In these animals, adrenocortical tumor progression was arrested; A cells and GATA-4 expression were evident, but there was no expression of LHR or P450 17 alpha-hydroxylase/C17-C20 lyase. Strain susceptibility to adrenocortical tumorigenesis (DBA/2J >> FVB/N) correlated with the expression of GATA-4 and LHR, implicating these factors in the process of adrenocortical neoplasia in response to continuous gonadotropin stimulation.

Adrenal Cortex↗
PubMed2002

Synthesis, purification and structural and functional characterization of recombinant form of a common genetic variant of human luteinizing hormone.

A common genetic variant (V) of luteinizing hormone (LH), with two mutations (Trp(8)Arg and Ile(15)Thr) and an extra glycosylation consensus site (Asn(13)-Ala-Thr), is associated with abnormalities of reproductive function. To address the molecular basis of the functional differences between V- and wild-type (WT)-LH, recombinant (rec) forms of WT- and V-LH were synthesized in human embryonic kidney (HEK 293) cells. The rec hormones synthesized were rigorously purified employing affinity, immunoaffinity and ion exchange chromatographies (final purity approximately 12 000 IU/mg, 180-fold purification, 28% recovery). Functional properties of the hormone preparations were compared in vitro and in vivo. The molecular size of both rec LHs was 31 kDa, as determined by SDS-PAGE. Although the mutations in V-LHbeta did not significantly affect the affinity of LH receptor (LHR) binding (Kd approximately 0.4 nmol/L), V-LH had higher in vitro biopotency than WT-LH, in terms of mLTC-1 mouse Leydig tumor cell cAMP and progesterone (P) production, and steroidogenic acute regulatory protein (StAR) expression. In addition, in HEK 293 cells expressing the human LHR, V-LH demonstrated 1.8-fold higher response of inositol trisphosphate (IP(3)) production than WT-LH. Furthermore, HEK 293 cells expressing the ElK1 trans-reporting plasmids displayed 2.7-fold greater luciferase response to V-LH than WT-LH, documenting stimulation of the mitogen-activated protein kinase (MAPK) pathway. The in vivo half-life of V-LH was clearly faster (5-9 min) than that of WT-LH (12-22 min) and human chorionic gonadotropin (hCG; 50-70 min), when injected into rat circulation. It is worth noting that analysis by matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS) demonstrated clear differences in structures of carbohydrate side chains attached to the two forms of rec LHs, including incomplete processing of high mannose glycans (Man(5,8,9)) in V-LH, suggesting different pathways in its intracellular trafficking. Collectively, the present findings provide the molecular basis for the qualitative and quantitative differences in LH action that are observed in carriers of the V-LHbeta allele.

Carbohydrate Conformation↗
PubMed2002

The role of mutations affecting gonadotrophin secretion and action in disorders of pubertal development.

A number of mutations that disturb the development and function of the hypothalamic-pituitary-gonadal (HPG) axis and cause disturbances in pubertal development are known today. These mutations have effects at all levels of the HPG axis, from the migration of gonadotrophin releasing hormone (GnRH) neurones from the nasal cavity to the hypothalamus, GnRH secretion, GnRH action, pituitary gonadotroph differentiation, gonadotrophin synthesis and secretion, right through to gonadotrophin action. Most of the mutations are inactivating, thus causing hypogonadism and arrest or delay of pubertal development. One exception is the activating mutations of the LH receptor, which causes the male-limited gonadotrophin-independent precocious puberty. The human mutations and animal models with disrupted function of orthologous genes have clarified the molecular pathogenesis of hypogonadism and disturbances of pubertal development. The correct diagnosis of these disorders using molecular biological techniques is now possible. This allows the selection of specific treatments and correct counselling of the patients and their families.

Adolescent↗
PubMed2002

Mechanisms of epidermal growth factor signaling: regulation of steroid biosynthesis and the steroidogenic acute regulatory protein in mouse Leydig tumor cells.

Steroid hormone biosynthesis in the adrenals and gonads is regulated by the steroidogenic acute regulatory (StAR) protein through its action in mediating the intramitochondrial transport of cholesterol. A role for epidermal growth factor (EGF) in modulating steroidogenesis has been previously determined, but the mechanism of its action remains unknown. The present investigation was designed to explore the potential mechanism of action of mouse EGF (mEGF) in the regulation of steroid biosynthesis and StAR protein expression in mLTC-1 mouse Leydig tumor cells. We show that treatment of mLTC-1 cells with mEGF significantly increased the levels of progesterone (P), StAR protein, and StAR mRNA in a time- and dose-dependent manner. The coordinate induction of P synthesis and StAR gene expression by mEGF was effectively inhibited by cycloheximide, indicating a requirement for de novo protein synthesis. Also, longer exposure of mLTC-1 cells to mEGF produced a marked decrease in LH-receptor mRNA expression. These effects of mEGF were exerted through high-affinity binding sites (K(d) approximately 0.53 nmol/L) in these cells. It was also determined that the arachidonic acid (especially lipoxygenase metabolites) and mitogen-activated protein kinase pathways were also involved in the mEGF-induced steroidogenic response. However, involvement of the latter pathway was further assessed in nonsteroidogenic COS-1 cells transfected with the Elk1 trans-reporting plasmids and resulted in a significant increase in luciferase activity in response to mEGF. Furthermore, deletion and mutational analyses demonstrated a predominant involvement of activator protein-1 in addition to the multiple mEGF responsive elements found within the 5'-flanking region (-151/-1 base pairs) of the mouse StAR gene. These findings provide novel insights into the mEGF-induced regulatory cascades associated with steroid synthesis and StAR protein expression in mouse Leydig cells.

Animals↗