Glial fibrillary acidic protein mutations in infantile, juvenile, and adult forms of Alexander disease

Alexander disease is a progressive, usually fatal neurological disorder defined by the widespread and abundant presence in astrocytes of protein aggregates called Rosenthal fibers. The disease most often occurs in infants younger than 2 years and has been labeled a leukodystrophy because of an accompanying severe myelin deficit in the frontal lobes. Later onset forms have also been recognized based on the presence of abundant Rosenthal fibers. In these cases, clinical signs and pathology can be quite different from the infantile form, raising the question whether they share the same underlying cause. Recently, we and others have found pathogenic, de novo missense mutations in the glial fibrillary acidic protein gene in most infantile patients examined and in a few later onset patients. To obtain further information about the role of glial fibrillary acidic protein mutations in Alexander disease, we analyzed 41 new patients and another 3 previously described clinically, including 18 later onset patients. Our results show that dominant missense glial fibrillary acidic protein mutations account for nearly all forms of this disorder. They also significantly expand the catalog of responsible mutations, verify the value of magnetic resonance imaging diagnosis, indicate an unexpected male predominance for the juvenile form, and provide insights into phenotype-genotype relations.

Both emerin and lamin C depend on lamin A for localization at the nuclear envelope

Physical interactions between lamins and emerin were investigated by co-immunoprecipitation of in vitro translated proteins. Emerin interacted with in vitro translated lamins A, B1 and C in co-immunprecipitation reactions. Competition reactions revealed a clear preference for interactions between emerin and lamin C. Structural associations between lamins and emerin were investigated in four human cell lines displaying abnormal expression and/or localisation of lamins A and C. In each cell line absence of lamins A and C from the nuclear envelope (NE) was correlated with mis-localisation of endogenous and exogenous emerin to the ER. In two cell lines that did not express lamin A but did express lamin C, lamin C as well as emerin was mis-localised. When GFP-lamin A was expressed in SW13 cells (which normally express only very low levels of endogenous lamin A and mis-localise endogenous emerin and lamin C), all three proteins became associated with the NE. When GFP-lamin C was expressed in SW13 cells neither the endogenous nor the exogenous lamin C was localised to the NE and emerin remained in the ER. Finally, lamins A and C were selectively eliminated from the NE of HeLa cells using a dominant negative mutant of lamin B1. Elimination of these lamins from the lamina led to the accumulation of emerin as aggregates within the ER. Our data suggest that lamin A is essential for anchorage of emerin to the inner nuclear membrane and of lamin C to the lamina.

Comparison of expression and regulation of the high-density lipoprotein receptor SR-BI and the low-density lipoprotein receptor in human adrenocortical carcinoma NCI-H295 cells

In rodents, cholesterol for adrenal steroidogenesis is derived mainly from high-density lipoproteins (HDL) via the HDL receptor, scavenger receptor-BI (SR-BI). In humans cholesterol for steroidogenesis is considered to be derived from the low-density lipoprotein (LDL) receptor pathway, and the contribution of SR-BI to that is unknown. In the present study SR-BI expression and regulation by steroidogenic stimuli was analysed in human adrenocortical cells and compared with LDL receptor expression. In addition, the functional contribution of both receptors for cholesteryl ester delivery to human adrenocortical cells was compared. Northern blot and reverse transcription-PCR amplification and sequence analysis demonstrated the presence of SR-BI mRNA in foetal and adult human adrenal cortex. Furthermore, SR-BI mRNA was expressed to similar levels in human primary adrenocortical and adrenocortical carcinoma NCI-H295 cells, indicating its presence in the steroid-producing cells. Treatment of NCI-H295 cells with 8Br-cAMP, a stimulator of glucocorticoid synthesis via the protein kinase A second messenger signal transduction pathway, resulted in an increase of both SR-BI and LDL receptor mRNA levels in a time- and dose-dependent manner. The induction of SR-BI and LDL receptor by cAMP was independent of ongoing protein synthesis and occurred at the transcriptional level. Ligand blot experiments indicated that a protein of similar size to SR-BI is the major HDL-binding protein in NCI-H295 cells. Western blot analysis demonstrated that cAMP treatment increased the levels of LDL receptor and, to a lesser extent, SR-BI protein in NCI-H295 cells. Binding and uptake of cholesterol was quantitatively smaller from HDL than from LDL, both in basal as well as in cAMP-stimulated cells. Scatchard analysis under basal conditions indicated that NCI-H295 cells express twice as many specific binding sites for LDL than for HDL. Dissociation constant values (Kd; in nm) were approximately five times higher for HDL than for LDL, indicating a lower affinity of HDL compared with LDL. The combined effects of these two parameters and the low cholesteryl ester content of HDL subfraction 3 (HDL3) contributes to a lower cholesteryl ester uptake from HDL than from LDL by the NCI-H295 cells. In conclusion, both the SR-BI and LDL receptor genes are expressed in the human adrenal cortex and coordinately regulated by activators of glucocorticoid synthesis. In contrast to rodents, in human adrenocortical cells the HDL pathway of cholesterol delivery appears to be of lesser importance than the LDL pathway. Nevertheless, the SR-BI pathway may become of major importance in conditions of functional defects in the LDL receptor pathway.

Alternate promoters and alternate splicing of human tenascin-X, a gene with 5' and 3' ends buried in other genes

Tenascin-X (TN-X) is an extracellular matrix protein encoded by a large gene that overlaps the steroid 21-hydroxylase (P450c21) gene in the HLA locus on chromosome 6p21.3. This may be the most complex locus in the human genome identified to date, containing 13 overlapping transcription units in 160 kb of DNA. Previous studies determined the sequence of 39 TN-X exons, encoding a 12 kb open reading frame, but the promoter(s) of the gene had not been located. We identify the principal TN-X promoter and a previously unknown 5' untranslated exon that lies more than 10 kb upstream from the previously known exons. This promoter, which is substantially different from the promoter for TN-C, initiates transcription in human fetal adrenal and muscle, but expression in human NCI-H295 adrenocortical carcinoma cells is initiated by two other promoters lying further upstream. One of these is the same as the promoter for a recently identified Creb-related protein (Creb-rp), but transcripts initiated form this promoter in human adrenal NCI-H295 tumor cells are spliced differently from Creb-rp, and are largely retained in the nuclei of these cells. By analogy with the other two members of the tenascin family, TN-C and TN-R, it has been predicted that TN-X should undergo alternate splicing in its fibronectin-like domains. RACE cloning and RNase protection experiments reveal no such alternate splicing. The TN-X gene appears to be unique in having both its 5' and 3' ends buried in other genes.

B-Type natriuretic peptide inhibited angiotensin II-stimulated cholesterol biosynthesis, cholesterol transfer, and steroidogenesis in primary human adrenocortical cells

In this study, we demonstrate that B-type natriuretic peptide (BNP) opposed angiotensin II (Ang II)-stimulated de novo cholesterol biosynthesis, cellular cholesterol uptake, cholesterol transfer to the inner mitochondrial membrane, and steroidogenesis, which are required for biosynthesis of steroid hormones such as aldosterone and cortisol in primary human adrenocortical cells. BNP dose-dependently stimulated intracellular cGMP production with an EC(50) of 11 nm, implying that human adrenocortical cells express the guanylyl cyclase A receptor. cDNA microarray and real-time RT-PCR analyses revealed that BNP inhibited Ang II-stimulated genes related to cholesterol biosynthesis (acetoacetyl coenzyme A thiolase, HMG coenzyme A synthase 1, HMG coenzyme A reductase, isopentenyl-diphosphate Delta-isomerase, lanosterol synthase, sterol-4C-methyl oxidase, and emopamil binding protein/sterol isomerase), cholesterol uptake from circulating lipoproteins (scavenger receptor class B type I and low-density lipoprotein receptor), cholesterol transfer to the inner mitochondrial membrane (steroidogenic acute regulatory protein), and steroidogenesis (ferredoxin 1,3beta-hydroxysteroid dehydrogenase, glutathione transferase A3, CYP19A1, CYP11B1, and CYP11B2). Consistent with the microarray and real-time PCR results, BNP also blocked Ang II-induced binding of (125)I-labeled low-density lipoprotein and (125)I-labeled high-density lipoprotein to human adrenocortical cells. Furthermore, BNP markedly inhibited Ang II-stimulated release of estradiol, aldosterone, and cortisol from cultured primary human adrenocortical cells. These findings demonstrate that BNP opposes Ang II-induced steroidogenesis via multiple steps from cholesterol supply and transfer to the final formation of steroid hormones. This study provides new insights into the cellular mechanisms by which BNP modulates Ang II-induced steroidogenesis in the adrenal gland.

CITED2 is expressed in human adrenocortical cells and regulated by basic fibroblast growth factor

CITED2 gene deletion in mice leads to adrenal agenesis. Therefore, we analyzed CITED2, a CBP/p300 interacting transactivator with transforming activity, in the human adrenal gland. In this study, we examined CITED2 expression in human embryonic and adult adrenal glands as well as adrenocortical carcinomas. As ACTH and basic fibroblast growth factor (bFGF) are connected to the physiology and growth of adrenocortical cells we studied the regulation of CITED2 by these factors in the NCI-H295R adrenocortical carcinoma cell line. We found CITED2 expression in the adult adrenal cortex as well in adrenocortical carcinomas. At an early stage of human adrenal organogenesis CITED2 could be located to the definitive zone of the developing adrenal gland using immunohistochemistry. In NCI-H295R cells, stimulation by bFGF led to a dose-dependent increase in CITED2 promotor activity, mRNA and protein expression while ACTH had no significant effect. The stimulatory effect of bFGF could be reduced by blocking mitogen-activated protein kinase activity using the MAPkinase kinase (MEK1)-inhibitor PD98059. CITED2 is expressed in embryonic and adult human adrenal glands as well as in adrenocortical cancer. It is connected to the signaling cascades of bFGF and its expression is modulated by mitogen-activated protein kinases. This suggests a novel role for CITED2 in human adrenal growth and possibly in adrenal tumorigenesis.

Steroidogenesis in the NCI-H295 Cell Line Model is Strongly Affected By Culture Conditions and Substrain

CONTEXT

NCI-H295 cells are the most widely used model for adrenal steroidogenesis and adrenocortical carcinoma and have been used for decades in laboratories worldwide. However, reported steroidogenic properties differ considerably.

OBJECTIVE

To evaluate heterogeneity of steroidogenesis among NCI-H295 cell strains, clarify the influence of culture media and test response to inhibitors of steroidogenesis by using liquid chromatography tandem mass spectrometry (LC-MS/MS).

METHODS

NCI-H295 cells were obtained from two cell banks and cultivated in different media. An LC-MS/MS-based panel analysis of thirteen steroids was adapted for cell culture supernatant. Cells were treated with metyrapone, abiraterone and mitotane.

RESULTS

Mineralocorticoid synthesis was strongly affected by passaging as reflected by reduction of aldosterone secretion from 0.158±0.006 to 0.017±0.001 µg/106 cells (p<0.05). Relevant differences were also found for cells from two vendors in terms of aldosterone secretion (0.180±0.001 vs. 0.09±0.002 µg/106 cells, p<0.05). Selection of medium strongly impacted on cortisol secretion with>4-fold difference (40.6±5.5 vs. 182.1±23 µg/106 cells) and reflected differential activation of the glucocorticoid pathway. Exposure to abiraterone, metyrapone and mitotane resulted in characteristic steroidogenic profiles consistent with known mechanism of drug action with considerable differences in metabolites upstream of the blocked enzyme.

CONCLUSION

We demonstrate that steroid hormone secretion in NCI-H295 cells is strongly affected by the individual strain, passage and growing conditions. These factors should be taken into account in the evaluation of experiments analyzing steroid parameters directly or as surrogate parameters of cell viability.