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N C Birnberg

Publications and source records attributed to N C Birnberg.

10 recordsLinked to original sources
PubMed1992

Expression of the c-Harvey ras oncogene alters peptide synthesis in the neurosecretory cell line AtT20.

Ras proteins are enriched in neurosecretory cells suggesting that ras may play an important role in regulating the differentiated properties of such cells. We introduced the human H-ras oncogene, EJ-ras, into the model secretory cell line AtT20 to determine the effects of ras oncogene expression on neuropeptide synthesis and release. We report here that both of these processes are changed in ras-transfected AtT20 cells. Stimulated release of the pituitary hormone corticotropin is reduced, and transcription of the gene encoding its precursor, proopiomelanocortin, is down-regulated. At the same time, expression of other genes, both housekeeping and neural-specific, remain relatively unchanged. The alteration of proopiomelanocortin expression in AtT20 cells following ras oncogene transformation supports the hypothesis that ras may play a role in the determination of the differentiated phenotype of neurosecretory cells.

Actins↗
PubMed1992

Expression of the H-ras oncogene induces potassium conductance and neuron-specific potassium channel mRNAs in the AtT20 cell line.

Expression of the EJ-ras oncogene in the AtT20 cell line results in several changes in their properties that correspond to a switch of these anterior pituitary-derived cells to a more neuronlike phenotype. The width of action potentials following transfection with ras is reduced 20-fold from over 200 msec in control AtT20 cells to less than 10 msec in ras-transfected cells. This is associated with a two- to threefold increase in the density of voltage-dependent potassium currents. In addition, the rate of inactivation of these currents is decreased approximately twofold in ras-transfected cells. At least part of the change in potassium current may be due to differential expression of potassium channel mRNAs. In the ras-transfected cells, mRNA species were detected using a probe for the voltage-dependent potassium channels, Kv4, a species that appears to be uniquely expressed in the nervous system, and NGK2, an alternatively spliced product transcribed from the same gene. These mRNAs are not detected in control AtT20 cells. The results suggest that the ras protein modulates the phenotype of excitable cells by influencing the expression of specific potassium channels and thereby altering the density and types of channels in the plasma membrane.

Electric Conductivity↗
PubMed1991

Dexamethasone increases potassium channel messenger RNA and activity in clonal pituitary cells.

Glucocorticoid hormones are released as part of the stress response and regulate secretion by the pituitary. Since the activity of ion channels also influences secretion, we examined the effect of the glucocorticoid agonist dexamethasone on ion channel expression. K+ channel mRNA was detected in rat hypothalamus and anterior pituitary, with probes derived from the rat Kv1 gene, a member of the mammalian voltage-gated K+ channel superfamily. High levels were also detected in PRL-secreting clonal (GH3 and GH4C1) rat pituitary cells. Dexamethasone rapidly increased the steady state concentration of Kv1 mRNA in GH3 cells in a dose-dependent manner. This change in gene expression was accompanied by an increase in whole cell voltage-gated K+ current [lk(i)] with similar pharmacology to the Kv1 gene product. Our findings indicate that hormones may act directly on excitable cells to produce long term effects on electrical activity and secretion by regulating K+ channel expression.

Animals↗
PubMed1990

Transfection of activated ras into an excitable cell line (AtT-20) alters tetrodotoxin sensitivity of voltage-dependent sodium current.

The sensitivity of voltage-dependent sodium current to the sodium channel blocker tetrodotoxin (TTX) is altered by transfection of a c-Ha-ras oncogene into an excitable cell line. Control AtT-20 cells, a cell line derived from a mouse anterior pituitary tumor, were found to express both a TTX-sensitive and a TTX-resistant sodium current. AtT-20 cells transfected with the c-Ha-ras gene expressed only a TTX-sensitive current. Properties of TTX-sensitive and -resistant currents were also examined. No differences in voltage dependence of activation or inactivation between the TTX-sensitive and -resistant currents were observed. The rate of inactivation of the TTX-resistant current in control cells was slower, than that of the TTX-sensitive current in either control or ras-transfected AtT-20 cells.

Dose-Response Relationship, Drug↗
PubMed1983

Glucocorticoids regulate proopiomelanocortin gene expression in vivo at the levels of transcription and secretion.

After adrenalectomy, the plasma levels of adrenocorticotropic hormone (corticotropin, ACTH)/endorphin peptides in rats rise dramatically in the first 4 hr while pituitary peptide levels fall sharply. Eight hours after adrenalectomy, plasma levels are near control values again but they then increase continuously over the next 8 days. Proopiomelanocortin (POMC) mRNA levels in the anterior pituitary (quantitated by hybridization with cloned POMC cDNA) increase 2-fold in the first 24 hours, reaching 15- to 20-fold the control level 18 days after adrenalectomy. When dexamethasone is administered to rats 8 days after adrenalectomy, the above events are reversed. Plasma ACTH falls to control levels within 2 hr whereas anterior pituitary POMC mRNA requires 5 days of treatment for return to control levels. The levels of POMC mRNA in the neurointermediate lobe and the hypothalamus are not altered by either treatment. Adrenalectomy increases transcription of the POMC gene in the anterior pituitary approximately 20-fold and halves transcription of the growth hormone gene within 1 hr of operation. Administration of dexamethasone immediately after adrenalectomy suppresses the increase in transcription of the POMC gene and increases the transcription of the growth hormone gene. Transcription of the POMC gene(s) in the neurointermediate lobe is not altered by either of these treatments.

Adrenalectomy↗
PubMed1982

Dramatic growth of mice that develop from eggs microinjected with metallothionein-growth hormone fusion genes.

A DNA fragment containing the promoter of the mouse metallothionein-I gene fused to the structural gene of rat growth hormone was microinjected into the pronuclei of fertilized mouse eggs. Of 21 mice that developed from these eggs, seven carried the fusion gene and six of these grew significantly larger than their littermates. Several of these transgenic mice had extraordinarily high levels of the fusion mRNA in their liver and growth hormone in their serum. This approach has implications for studying the biological effects of growth hormone, as a way to accelerate animal growth, as a model for gigantism, as a means of correcting genetic disease, and as a method of farming valuable gene products.

Animals↗
PubMed1982

Glucocorticoid and thyroid hormones transcriptionally regulate growth hormone gene expression.

In order to define the molecular mechanisms by which glucocorticoids and thyroid hormone act to regulate growth hormone gene expression, the sites at which they exert their effects on growth hormone biosynthesis were examined in vivo and in a pituitary cell line. Glucocorticoids were shown to rapidly increase accumulation of growth hormone mRNA and nuclear RNA precursors. Glucocorticoids and thyroid hormone were shown to rapidly and independently increase growth hormone gene transcription. These events are shown to occur physiologically in animals and further establish the importance of growth hormone gene expression as a model for steroid regulation.

Cell Line↗
PubMedDate not supplied

A cyclic AMP- and phorbol ester-inducible DNA element.

Many cellular processes are regulated by hormones and neurotransmitters which interact with cell-surface receptors to produce intracellular second messengers that activate protein kinases. Cyclic (c) AMP is a second messenger whose intracellular level is determined by receptor-mediated activation or inhibition of adenylate cyclase. Phorbol esters directly activate protein kinase C, a Ca2+ and phospholipid-dependent protein kinase and a component of a different second messenger system, the phosphatidylinositol pathway. Proenkephalin messenger RNA levels are regulated in response to cAMP analogues, activators of adenylate cyclase, nicotinic agonists and depolarization, suggesting that expression of the gene encoding proenkephalin is regulated by trans-synaptic events involving cell-surface-receptor activation. Here we report that cAMP analogues and activators of adenylate cyclase regulate a proenkephalin-chloramphenicol acetyl transferase fusion gene when transiently expressed in tissue culture cells. Phorbol ester regulates the fusion gene in a similar fashion, but requires the presence of phosphodiesterase inhibitors for large effects. The DNA sequences required for regulation by both cAMP and phorbol ester map to the same 37-base pair (bp) region located 107-71 bp 5' to the mRNA cap site of the proenkephalin gene. This highly conserved region is composed of three closely related 12-bp sequences and has properties similar to those of previously characterized transcriptional enhancers.

Acetyltransferases↗