Gene mutations in the succinate dehydrogenase subunit SDHB cause susceptibility to familial pheochromocytoma and to familial paraganglioma

The pheochromocytomas are an important cause of secondary hypertension. Although pheochromocytoma susceptibility may be associated with germline mutations in the tumor-suppressor genes VHL and NF1 and in the proto-oncogene RET, the genetic basis for most cases of nonsyndromic familial pheochromocytoma is unknown. Recently, pheochromocytoma susceptibility has been associated with germline SDHD mutations. Germline SDHD mutations were originally described in hereditary paraganglioma, a dominantly inherited disorder characterized by vascular tumors in the head and the neck, most frequently at the carotid bifurcation. The gene products of two components of succinate dehydrogenase, SDHC and SDHD, anchor the gene products of two other components, SDHA and SDHB, which form the catalytic core, to the inner-mitochondrial membrane. Although mutations in SDHC and in SDHD may cause hereditary paraganglioma, germline SDHA mutations are associated with juvenile encephalopathy, and the phenotypic consequences of SDHB mutations have not been defined. To investigate the genetic causes of pheochromocytoma, we analyzed SDHB and SDHC, in familial and in sporadic cases. Inactivating SDHB mutations were detected in two of the five kindreds with familial pheochromocytoma, two of the three kindreds with pheochromocytoma and paraganglioma susceptibility, and 1 of the 24 cases of sporadic pheochromocytoma. These findings extend the link between mitochondrial dysfunction and tumorigenesis and suggest that germline SDHB mutations are an important cause of pheochromocytoma susceptibility.

Neuronal apoptosis linked to EglN3 prolyl hydroxylase and familial pheochromocytoma genes: developmental culling and cancer

Germline NF1, c-RET, SDH, and VHL mutations cause familial pheochromocytoma. Pheochromocytomas derive from sympathetic neuronal precursor cells. Many of these cells undergo c-Jun-dependent apoptosis during normal development as NGF becomes limiting. NF1 encodes a GAP for the NGF receptor TrkA, and NF1 mutations promote survival after NGF withdrawal. We found that pheochromocytoma-associated c-RET and VHL mutations lead to increased JunB, which blunts neuronal apoptosis after NGF withdrawal. We also found that the prolyl hydroxylase EglN3 acts downstream of c-Jun and is specifically required among the three EglN family members for apoptosis in this setting. Moreover, EglN3 proapoptotic activity requires SDH activity because EglN3 is feedback inhibited by succinate. These studies suggest that failure of developmental apoptosis plays a role in pheochromocytoma pathogenesis.

A role for mitochondrial enzymes in inherited neoplasia and beyond

Mitochondrial defects have been associated with neurological disorders, as well as cancers. Two ubiquitously expressed mitochondrial enzymes--succinate dehydrogenase (SDH) and fumarate hydratase (FH, fumarase)--catalyse sequential steps in the Krebs tricarboxylic-acid cycle. Inherited heterozygous mutations in the genes encoding these enzymes cause predispositions to two types of inherited neoplasia syndromes that do not share any component tumours. Homozygous mutations in the same genes result in severe neurological impairment. Understanding this link between inherited cancer syndromes and neurological disease could provide further insights into the mechanisms by which mitochondrial deficiencies lead to tumour development.

A single human gene encoding multiple tyrosine hydroxylases with different predicted functional characteristics

Catecholaminergic systems in discrete regions of the brain are thought to be important in affective psychoses, learning and memory, reinforcement and sleep-wake cycle regulation. Tyrosine hydroxylase (TH) is the first enzyme in the pathway of catecholamine synthesis. Its importance is reflected in the diversity of the mechanisms that have been described which control its activity; TH levels vary both during development and as a function of the activity of the nervous system. Recently, we deduced the complete amino-acid sequence of rat TH from a complementary DNA clone encoding a functional enzyme. Here we demonstrate that, in man, TH molecules are encoded by at least three distinct messenger RNAs. The expression of these mRNAs varies in different parts of the nervous system. The sequence differences observed are confined to the 5' termini of the messengers and involve alternative splicing events. This variation has clear functional consequences for each putative form of the enzyme and could represent a novel means of regulating catecholamine levels in normal and pathological neurons.

Nerve growth factor-mediated stimulation of tyrosine hydroxylase activity in a clonal rat pheochromocytoma cell line

In order to confirm the multiple neurotransmitter biosynthetic ability, the possibility to separation of the activities of tyrosine hydroxylase (TH), choline acetyltransferase and glutamic acid decarboxylase was tested by subcloning of a clonal rat pheochromocytoma PC12 cell line. All of 9 subclones obtained showed significant activities of above 3 enzymes, indicating that the PC12 cell has multi-functional properties of neurotransmitter syntheses. One of the subclones, designated PC12h, was demonstrated to have nerve growth factor- (NGF) responsive TH activity. The ED50 value of NGF to increase the TH activity was 1.7 ng/ml (6.5 X 10-11 M). A simultaneous addition of saturating amounts of NGF (50 ng/ml) and dexamethasone (10-6 M) resulted in the increase of TH activity that is equal to the sum of those achieved when either effector was added separately, indicating that the NGF- mediated increase of TH activity in PC12h cells was independent upon the effect of dexamethasone. And also, the TH activity increased by NGF was somewhat potentiated in PC12h cells cultured in a hormone- supplemented serum-free medium.

Functional consequences of a SDHB gene mutation in an apparently sporadic pheochromocytoma

Three genes encoding for mitochondrial complex II proteins are linked to hereditary paraganglioma. We have recently shown that an inactivation of the SDHD gene is associated with a complete loss of mitochondrial complex II activity and a stimulation of the angiogenic pathway (Gimenez-Roqueplo, A. P., J. Favier, P. Rustin, J. J. Mourad, P. F. Plouin, P. Corvol, A. Rötig, and X. Jeunemaitre, 2001, Am J Hum Genet 69:1186-1197). Here, we relate the case of a malignant sporadic pheochromocytoma induced by a germline missense mutation of the SDHB gene. Within the tumor, a loss of heterozygosity at chromosome 1pter led to a null SDHB allele and to a complete loss of complex II enzymatic activity. In situ hybridization and immunohistochemistry experiments showed a high expression of hypoxic-angiogenic responsive genes, similar to that previously observed in inherited-SDHD tumors. This observation highlights the role of the complex II mitochondrial genes in the oxygen-sensing pathway and in the regulation of angiogenesis of neural crest-derived tumors.

Pheochromocytoma: the expanding genetic differential diagnosis

Pheochromocytomas and paragangliomas are tumors of the autonomic nervous system; pheochromocytomas are tumors of the adrenal medulla, and paragangliomas are extra-adrenal tumors arising from either the sympathetic nervous system or parasympathetic ganglia. It has previously been estimated that approximately 10%-15% of pheochromocytomas are due to hereditary causes. However, our increased understanding of the three hereditary syndromes (neurofibromatosis 1, multiple endocrine neoplasia type 2, and von Hippel-Lindau syndrome) in which pheochromocytoma is found and the recent discovery that mutations in genes in the succinate dehydrogenase family (SDHB and SDHD) predispose to pheochromocytoma have necessitated a re-evaluation of the genetic basis of pheochromocytoma. These studies indicate that the frequency of germline mutations associated with isolated pheochromocytoma is higher than previously estimated, with both hospital-based series and a large population-based series indicating that the frequency of germline mutations in RET, VHL, SDHB, and SDHD taken together approximates 20%. In all patients with pheochromocytoma, including those with known hereditary syndrome or a positive family history, the frequency of germline mutations in these four genes together approaches 30%. Given the frequency of germline mutations, consideration should be given to genetic counseling for all patients with pheochromocytoma and is particularly important for individuals with a positive family history, multifocal disease, or a diagnosis before age 50. Identification of patients with hereditary pheochromocytoma is important because it can guide medical management in mutation-positive patients and their families. This review provides an overview of the known genetic syndromes that are commonly associated with pheochromocytoma, examines recent data on the association of germline mutations in the succinate dehydrogenase gene family with pheochromocytoma, and suggests guidelines for the genetic evaluation of pheochromocytoma patients.

Nerve growth factor induces protein-tyrosine phosphorylation

When the sympathetic nerve-like cell line PC12 is exposed to nerve growth factor (NGF), there is a rapid and transient phosphorylation of tyrosine residues in cellular proteins, as demonstrated by immunoblotting of cell extracts with high-affinity polyclonal antibodies specific for phosphotyrosine residues. Epidermal growth factor (EGF), which does not cause the morphological differentiation of PC12 cells that is produced by NGF, also induces protein-tyrosine phosphorylation. The methyltransferase inhibitor, 5'-methylthioadenosine, which is known to block the NGF-mediated morphological differentiation of PC12 cells, also inhibits the induction of protein-tyrosine phosphorylation by NGF. 5'-Methylthioadenosine has no effect, however, on EGF-stimulated phosphorylation of tyrosine residues in cellular proteins. In addition, low temperature markedly slows the rate of protein-tyrosine phosphorylation stimulated by NGF, but it has no effect on the time course of protein-tyrosine phosphorylation induced by EGF. These data suggest that NGF and EGF induce protein-tyrosine phosphorylation in PC12 cells by different mechanisms.

Tyrosine hydroxylase: a substrate of cyclic AMP-dependent protein kinase

Data demonstrating the direct phosphorylation of tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] purified from rat pheochromocytoma by ATP, Mg2+ and cyclic AMP-dependent protein kinase catalytic subunit are presented. The incorporation of phosphate is highly correlated with the activation of the hydroxylase when either the time of preincubation or the amount of protein kinase subunit is varied. The rate of phosphorylation of tyrosine hydroylase compares favorably with that of H1 histone, a known substrate of protein kinase. Lineweaver-Burk analysis of crude or purified rat pheochromocytoma tyrosine hydroxylase activity, as a function of pterin cofactor concentration, in the absence of ATP, Mg2+, and protein kinase catalytic subunit, yields a curvilinear relationship which can be resolved into two lines, suggesting two enzyme forms with different affinities for pterin cofactor. A fraction of the hydroxylase present in the tumor exists in the activated state, presumably due to the presence of ATP and endogenous protein kinase activity. When the solubl enzyme is activated by cyclic AMP, ATP, Mg2+, and protein kinase, virtually all of the enzyme is converted to the low Km state. We conclude that tyrosine hydroxylase is a substrate of cyclic AMP-dependent protein kinase in vitro and, presumably, in vivo.

Isolation of a novel cDNA clone for human tyrosine hydroxylase: alternative RNA splicing produces four kinds of mRNA from a single gene

Human tyrosine hydroxylase (TH) cDNA was isolated by molecular cloning. Lambda gt 11 cDNA library constructed from human pheochromocytoma was screened with a synthetic 23-mer oligonucleotide complementary to rat TH mRNA. We found a novel type of cDNA clone whose N-terminal sequence is similar to but clearly distinct from each of the three types (type 1, 2 and 3) of TH cDNA reported by Grima et al. [Nature (1987) 326, 707-711]. It contains both the 12-bp insert characteristic of type 2 cDNA and the 81-bp sequence of type 3. This novel cDNA clone was designated as type 4. Southern blot analysis of human genomic DNA indicated that TH is encoded by a single gene. This suggests that the four different forms of TH mRNA are produced by alternative RNA splicing from a single primary transcript.

Plasma metanephrines are markers of pheochromocytoma produced by catechol-O-methyltransferase within tumors

This study examined whether the high sensitivity of plasma free metanephrines for diagnosis of pheochromocytoma may result from production of free metanephrines within tumors. Presence in pheochromocytomas of catechol-O-methyltransferase (COMT), the enzyme responsible for conversion of catecholamines to metanephrines, was confirmed by Western blot analysis, enzyme assay, and immunohistochemistry. Western blot analysis and enzyme assay indicated that membrane-bound and not soluble COMT was the predominant form of the enzyme in pheochromocytoma. Immunohistochemistry revealed colocalization of COMT in the same chromaffin cells where catecholamines are translocated into storage vesicles by the vesicular monoamine transporter. Levels of free metanephrines in pheochromocytoma over 10,000 times higher than plasma concentrations in the same patients before removal of tumors indicated production of metanephrines within tumors. Comparisons of the production of metanephrines in patients with pheochromocytoma with production from catecholamines released or infused into the circulation indicated that more than 93% of the consistently elevated levels of circulating free metanephrines in patients with pheochromocytoma are derived from metabolism before and not after release of catecholamines into the circulation. The data indicate that the elevated plasma levels of free metanephrines in patients with pheochromocytoma are derived from catecholamines produced and metabolized within tumors. Some tumors do not secrete catecholamines, but all appear to metabolize catecholamines to free metanephrines, thus explaining the better sensitivity of plasma free metanephrines over other tests for diagnosis of pheochromocytoma.

5' flanking DNA sequences direct cell-specific expression of rat tyrosine hydroxylase

Tyrosine hydroxylase (TH) is selectively expressed in catecholaminergic neurons and in chromaffin cells of the adrenal medulla. Constructs in which 5' flanking sequences of the rat TH gene directed expression of bacterial chloramphenicol acetyltransferase (CAT) were transfected into cell lines and assayed for transient expression of CAT. In most nonexpressing cell lines, CAT levels were less than 5% of that found in a TH-positive pheochromocytoma line (PC8b). In two lines described here, a rat anterior pituitary cell line (GH4) and a rat fibroblast line (Fr3T3), CAT expression reached 12 and 20%, respectively, of the PC8b level. Greater than 90% of the PC8b activity was lost when sequences between -212 and -187 (in relation to the transcriptional initiation site) were deleted. Further deletions that removed the cyclic AMP response element (CRE) (-45) and the TATA box at -29 reduced transcriptional activity to background in all three lines. These data suggest that 212 nucleotides of the 5' sequence are sufficient for pheochromocytoma expression and that information between -212 and -187, which includes an AP1 site (-206 to -200), is essential for full transcriptional activity. In addition, sites for other protein transcription factors (AP2, POU/Oct, SP1, and CRE) reside between -221 and -38 and are largely conserved between the human and rat gene.

Krebs cycle metabolite profiling for identification and stratification of pheochromocytomas/paragangliomas due to succinate dehydrogenase deficiency

CONTEXT

Mutations of succinate dehydrogenase A/B/C/D genes (SDHx) increase susceptibility to development of pheochromocytomas and paragangliomas (PPGLs), with particularly high rates of malignancy associated with SDHB mutations.

OBJECTIVE

We assessed whether altered succinate dehydrogenase product-precursor relationships, manifested by differences in tumor ratios of succinate to fumarate or other metabolites, might aid in identifying and stratifying patients with SDHx mutations.

DESIGN, SETTING, AND PATIENTS

PPGL tumor specimens from 233 patients, including 45 with SDHx mutations, were provided from eight tertiary referral centers for mass spectrometric analyses of Krebs cycle metabolites.

MAIN OUTCOME MEASURE

Diagnostic performance of the succinate:fumarate ratio for identification of pathogenic SDHx mutations.

RESULTS

SDH-deficient PPGLs were characterized by 25-fold higher succinate and 80% lower fumarate, cis-aconitate, and isocitrate tissue levels than PPGLs without SDHx mutations. Receiver-operating characteristic curves for use of ratios of succinate to fumarate or to cis-aconitate and isocitrate to identify SDHx mutations indicated areas under curves of 0.94 to 0.96; an optimal cut-off of 97.7 for the succinate:fumarate ratio provided a diagnostic sensitivity of 93% at a specificity of 97% to identify SDHX-mutated PPGLs. Succinate:fumarate ratios were higher in both SDHB-mutated and metastatic tumors than in those due to SDHD/C mutations or without metastases.

CONCLUSIONS

Mass spectrometric-based measurements of ratios of succinate:fumarate and other metabolites in PPGLs offer a useful method to identify patients for testing of SDHx mutations, with additional utility to quantitatively assess functionality of mutations and metabolic factors responsible for malignant risk.

Impaired neurotransmitter uptake in PC12 cells overexpressing human Cu/Zn-superoxide dismutase--implication for gene dosage effects in Down syndrome

Rat PC12 cells expressing elevated levels of transfected human Cu/Zn-superoxide dismutase (CuZn-SOD) gene were generated. These transformants (designated PC12-hSOD) closely resembled the parental cells in their morphology, growth rate, and response to nerve growth factor, but showed impaired neurotransmitter uptake. The lesion was localized to the chromaffin granule transport mechanism. We found that the pH gradient (delta pH) across the membrane, which is the main driving force for amine transport, was diminished in PC12-hSOD granules. These results show that elevation of CuZnSOD activity interferes with the transport of biogenic amines into chromaffin granules. Since neurotransmitter uptake plays an important role in many processes of the central nervous system, CuZnSOD gene-dosage may contribute to the neurobiological abnormalities of Down's syndrome.

Deficiency in a mitochondrial aldehyde dehydrogenase increases vulnerability to oxidative stress in PC12 cells

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) plays a major role in acetaldehyde detoxification. The alcohol sensitivity is associated with a genetic deficiency of ALDH2. We have previously reported that this deficiency influences the risk for late-onset Alzheimer's disease. However, the biological effects of the deficiency on neuronal cells are poorly understood. Thus, we obtained ALDH2-deficient cell lines by introducing mouse mutant Aldh2 cDNA into PC12 cells. The mutant ALDH2 repressed mitochondrial ALDH activity in a dominant negative fashion, but not cytosolic activity. The resultant ALDH2-deficient transfectants were highly vulnerable to exogenous 4-hydroxy-2-nonenal, an aldehyde derivative generated by the reaction of superoxide with unsaturated fatty acid. In addition, the ALDH2-deficient transfectants were sensitive to oxidative insult induced by antimycin A, accompanied by an accumulation of proteins modified with 4-hydroxy-2-nonenal. Thus, these findings suggest that mitochondrial ALDH2 functions as a protector against oxidative stress.

Human serum dopamine- -hydroxylase. Relationship to hypertension and sympathetic activity

Serum dopamine-β-hydroxylase activity varied from 3 to 581 units/ml in a group of 168 untreated adults (90 normals, 78 with borderline or overt hypertension). Levels did not correlate with blood pressure or age, but mean values were significantly lower in blacks than they were in whites. Subjects with exceptionally low levels of serum dopamine-β-hydroxylase activity showed normal cardiovascular function and normal β-hydroxylation of an administered synthetic substrate, hydroxyamphetamine. Pronounced blood pressure reduction by antihypertensive drugs did not change serum dopamine-β-hydroxylase activity, and intensive bicycle exercise produced only small and variable increases. Two subjects with severe sympathetic dysfunction, i.e., orthostatic hypotension, showed normal levels of dopamine-β-hydroxylase activity (89-123 units/ml). Serum dopamine-β-hydroxylase activity varied from 450 to 950 units/ml in five subjects with pheochromocytomas and decreased to one-tenth the preoperative level in one subject who underwent curative surgery. Therefore, serum dopamine-β-hydroxylase activity is not a satisfactory index of sympathetic function; moreover, activity levels do not correlate with prevailing blood pressure. Subjects with pheochromocytomas, however, may show increased serum levels of the enzyme, which demonstrates that such tumors can release dopamine-β-hydroxylase.

Neuritic growth from a new subline of PC12 pheochromocytoma cells: cyclic AMP mimics the action of nerve growth factor

We have identified a new subline of PC12 pheochromocytoma cells (PC12D cells) in which neurites are extended within 24 hr in response to cAMP-enhancing reagents as well as in response to nerve growth factor (NGF), but not in response to epidermal growth factor or phorbol diester. Anti-NGF antiserum did not affect forskolin (FRK)-induced neuritic recruitment. FRK-induced neurites exhibited growth cones and contained secretion granules and many parallel arrays of microtubules as was the case with NGF-induced neurites. FRK, but not NGF, increased the levels of intracellular cAMP and activated adenylate cyclase in the membrane fraction. Both NGF and FRK enhanced the activities of tyrosine hydroxylase (TH), acetylcholinesterase (AchE), and ornithine decarboxylase (ODC), but not the levels of neuron-specific enolase. Enhanced levels of intracellular cAMP mimicked the effects of NGF on neuritic growth, TH, AchE, and ODC activities in PC12D cells, even though NGF does not act through elevation of levels of cAMP.

Isolation and characterization of a cDNA clone encoding human aromatic L-amino acid decarboxylase

The nucleotide sequence of a cDNA clone that includes the entire coding region of human aromatic L-amino acid decarboxylase gene is presented. A human pheochromocytoma cDNA library was screened using an oligonucleotide probe which corresponded to a partial amino acid sequence of the enzyme purified from the human pheochromocytoma. The isolated cDNA clone encoded a protein of 480 amino acids with a calculated molecular mass of 53.9 kDa. The amino acid sequence Asn-Phe-Asn-Pro-His-Lys-Trp around a possible cofactor (pyridoxal phosphate) binding site is identical in human, Drosophila, and pig enzymes.

The primary structure of human dopamine-beta-hydroxylase: insights into the relationship between the soluble and the membrane-bound forms of the enzyme

A full length dopamine-beta-hydroxylase (DBH) cDNA clone was isolated from a human pheochromocytoma lambda gt11 library. Both structural and functional evidence confirms the authenticity of the clone: (i) antibodies selected with fusion proteins generated by positive clones precipitate DBH activity, (ii) the sequence of three internal DBH tryptic peptides are included in the deduced DBH sequence, (iii) the previously reported N-terminal 15 amino acids of bovine DBH exhibits a nearly complete identity with that predicted for human DBH. The polypeptide chain of DBH comprises 578 amino acids corresponding to an unmodified protein of 64 862 daltons and is preceded by a cleaved signal peptide of 25 residues. DBH exists in both membrane-bound and soluble forms. The hydropathy plot reveals no obvious hydrophobic segment, except the signal peptide. S1 mapping analysis indicates no diversity in the 5' and 3' extremities of the DBH mRNA. Taken together with available biochemical data, these observations suggest that the membrane attachment of DBH probably results from a post-translational modification, glypiation being the most likely candidate. Comparative amino acid sequence analysis establishes that DBH shares no homology with the other catecholamine synthesizing enzymes, tyrosine hydroxylase and phenylethanolamine-N-methyl transferase.

The action of adenosine analogs on PC12 cells

PC12 cells, a nerve growth factor-responsive clone of rat pheochromocytoma, contain a membrane-bound adenylate cyclase, which can be activated by adenosine analogs. The characteristics of the cyclase response indicate the presence of stimulatory adenosine receptors. Adenosine analogs also produce a marked increase in the ornithine decarboxylase levels of the cells, and the characteristics of this response suggest that it is linked to the adenylate cyclase-stimulatory adenosine receptors. The ornithine decarboxylase response elicited by 5'-N-ethylcarboxamideadenosine (NECA), a potent stimulatory adenosine analog, is synergistic with that produced by nerve growth factor. Differentiation of the cells with nerve growth factor, however, does not substantially alter either the response of cyclase to the adenosine analog or the magnitude of the adenosine-evoked ornithine decarboxylase response. Treatment of the cells with NECA produces an increase in the phosphorylation of a specific non-histone nuclear protein. While causing little or no morphological alteration by itself, NECA is synergistic with nerve growth factor in producing neurite outgrowth in PC12 cells. NECA does not cause an induction of acetylcholinesterase in the cells. NECA does not cause an induction of acetylcholinesterase in the cells, nor does it appear to affect the induction of this enzyme by nerve growth factor.

Monoclonal antibodies to tyrosine hydroxylase from rat pheochromocytoma PC12h cells with special reference to nerve growth factor-mediated increase of the immunoprecipitable enzymes

Twelve hybridomas, which secrete the monoclonal antibodies to rat pheochromocytoma tyrosine hydroxylase (TH), were obtained. All of these antibodies immunoprecipitated the TH molecules from rat pheochromocytoma PC12h cells, adrenal medulla and brain. Two antibodies, namely PCTH-3 and -7 (both IgG1), directly inhibited the catalytic activity of TH. Another antibody, PCTH-4 (IgG1), bound to the enzyme without inhibition of the catalytic activity. The antibodies PCTH-3 and -4 immunostained the 60 K bands on a nitrocellulose sheet, which were electrotransfered from the gel after the SDS-polyacrylamide gel electrophoresis of PC12h cell and rat adrenal medulla homogenates. The antibody PCTH-4 immunocytochemically labeled specific neurons in the locus ceruleus, hypothalamus and substantia nigra of rat brain. Immunotitration using PCTH-4 antibody revealed that the nerve growth factor-mediated increase of TH activity in PC12h cells is due to the increase of the enzyme molecules.