Akt, a target of phosphatidylinositol 3-kinase, inhibits apoptosis in a differentiating neuronal cell line.

Phosphatidylinositol (PI) 3-kinase has been suggested to mediate cell survival. Consistent with this possibility, apoptosis of conditionally (simian virus 40 Tts) immortalized rat hippocampal H19-7 neuronal cells was increased in response to wortmannin, an inhibitor of PI 3-kinase. Downstream effectors of PI 3-kinase include Rac1, protein kinase C, and the serine-threonine kinase Akt (protein kinase B). Here, we show that activation of Akt is one mechanism by which PI 3-kinase can mediate survival of H19-7 cells during serum deprivation or differentiation. While ectopic expression of wild-type Akt (c-Akt) does not significantly enhance survival in H19-7 cells, expression of activated forms of Akt (v-Akt or myristoylated Akt) results in enhanced survival which can be comparable to that conferred by Bcl-2. Conversely, expression of a dominant-negative mutant of Akt accelerates cell death upon serum deprivation or differentiation. Finally, the results indicate that Akt can transduce a survival signal for differentiating neuronal cells through a mechanism that is independent of induction of Bcl-2 or Bcl-XL or inhibition of Jun kinase activity.

Different protein kinase C isoforms determine growth factor specificity in neuronal cells.

Although mitogenic and differentiating factors often activate a number of common signaling pathways, the mechanisms leading to their distinct cellular outcomes have not been elucidated. In a previous report, we demonstrated that mitogen-activated protein (MAP) kinase (ERK) activation by the neurogenic agents fibroblast growth factor (FGF) and nerve growth factor is dependent on protein kinase Cdelta (PKCdelta), whereas MAP kinase activation in response to the mitogen epidermal growth factor (EGF) is independent of PKCdelta in rat hippocampal (H19-7) and pheochromocytoma (PC12) cells. We now show that EGF activates MAP kinase through a PKCzeta-dependent pathway involving phosphatidylinositol 3-kinase and PDK1 in H19-7 cells. PKCzeta, like PKCdelta, acts upstream of MEK, and PKCzeta can potentiate Raf-1 activation by EGF. Inhibition of PKCzeta also blocks EGF-induced DNA synthesis as monitored by bromodeoxyuridine incorporation in H19-7 cells. Finally, in embryonic rat brain hippocampal cell cultures, inhibitors of PKCzeta or PKCdelta suppress MAP kinase activation by EGF or FGF, respectively, indicating that these factors activate distinct signaling pathways in primary as well as immortalized neural cells. Taken together, these results implicate different PKC isoforms as determinants of growth factor signaling specificity within the same cell. Furthermore, these data provide a mechanism whereby different growth factors can differentially activate a common signaling intermediate and thereby generate biological diversity.

Raf, but not MEK or ERK, is sufficient for differentiation of hippocampal neuronal cells.

To elucidate signal transduction pathways leading to neuronal differentiation, we have investigated a conditionally immortalized cell line from rat hippocampal neurons (H19-7) that express a temperature sensitive simian virus 40 large T antigen. Treatment of H19-7 cells with the differentiating agent basic fibroblast growth factor at 39 degrees C, the nonpermissive temperature for T function, resulted in the activation of c-Raf-1, MEK, and mitogen-activated protein (MAP) kinases (ERK1 and -2). To evaluate the role of Raf-1 in neuronal cell differentiation, we stably transfected H19-7 cells with v-raf or an oncogenic human Raf-1-estrogen receptor fusion gene (deltaRaf-1:ER). deltaRaf-1:ER transfectants in the presence of estradiol for 1 to 2 days expressed a differentiation phenotype only at the nonpermissive temperature. However, extended exposure of the deltaRaf-1:ER transfectants to estradiol or stable expression of the v-raf construct yielded cells that extended processes at the permissive as well as the nonpermissive temperature, suggesting that cells expressing the large T antigen are capable of responding to the Raf differentiation signal. deltaRaf-1:ER, MEK, and MAP kinase activities in the deltaRaf-1:ER cells were elevated constitutively for up to 36 h of estradiol treatment at the permissive temperature. At the nonpermissive temperature, MEK and ERKs were activated to a significantly lesser extent, suggesting that prolonged MAP kinase activation may not be sufficient for differentiation. To test this possibility, H19-7 cells were transfected or microinjected with constitutively activated MEK. The results indicate that prolonged activation of MEK or MAP kinases (ERK1 and -2) is not sufficient for differentiation of H19-7 neuronal cells and raise the possibility that an alternative signaling pathway is required for differentiation of H19-7 cells by Raf.

Practical aspects of complex permittivity reconstruction with neural-network-controlled FDTD modeling of a two-port fixture.

The paper discusses characteristics of a new modeling-based technique for determining dielectric properties of materials. Complex permittivity is found with an optimization algorithm designed to match complex S-parameters obtained from measurements and from 3D FDTD simulation. The method is developed on a two-port (waveguide-type) fixture and deals with complex reflection and transmission characteristics at the frequency of interest. A computational part is constructed as an inverse-RBF-network-based procedure that reconstructs dielectric constant and the loss factor of the sample from the FDTD modeling data sets and the measured reflection and transmission coefficients. As such, it is applicable to samples and cavities of arbitrary configurations provided that the geometry of the experimental setup is adequately represented by the FDTD model. The practical implementation of the method considered in this paper is a section of a WR975 waveguide containing a sample of a liquid in a cylindrical cutout of a rectangular Teflon cup. The method is run in two stages and employs two databases--first, built for a sparse grid on the complex permittivity plane, in order to locate a domain with an anticipated solution and, second, made as a denser grid covering the determined domain, for finding an exact location of the complex permittivity point. Numerical tests demonstrate that the computational part of the method is highly accurate even when the modeling data is represented by relatively small data sets. When working with reflection and transmission coefficients measured in an actual experimental fixture and reconstructing a low dielectric constant and the loss factor the technique may be less accurate. It is shown that the employed neural network is capable of finding complex permittivity of the sample when experimental data on the reflection and transmission coefficients are numerically dispersive (noise-contaminated). A special modeling test is proposed for validating the results; it confirms that the values of complex permittivity for several liquids (including salt water acetone and three types of alcohol) at 915 MHz are reconstructed with satisfactory accuracy.

Insulin-like growth factor I receptor signaling in differentiation of neuronal H19-7 cells.

The type I insulin-like growth factor receptor (IGF-IR) is known to send two seemingly contradictory signals inducing either cell proliferation or cell differentiation, depending on cell type and/or conditions. H19-7 cells are rat hippocampal neuronal cells immortalized by a temperature-sensitive SV40 large T antigen that grow at 34 degrees C in epidermal growth factor or serum but differentiate at 39 degrees C when induced by basic fibroblast growth factor. At 39 degrees C, expression of the human IGF-IR in H19-7 cells induces an insulin-like growth factor (IGF) I-dependent differentiation. We have investigated the domains of the IGF-IR required for differentiation of H19-7 cells. The tyrosine 950 residue and serines 1280-1283 in the COOH terminus of the receptor are required for IGF-I-induced differentiation at 39 degrees C, although they are dispensable for IGF-I-mediated growth at 34 degrees C. Both domains have to be mutated to inactivate the differentiating function. The inability of these mutant receptors to induce differentiation correlates with mitogen-activated protein kinase activation. In contrast, inhibitors of phosphatidylinositol 3'-kinase have no effect on IGF-I-mediated differentiation of H19-7 cells, although they do inhibit the mitogenic response.

FGF induces a switch in death receptor pathways in neuronal cells.

Basic fibroblast growth factor (FGF2) has many roles in neuronal development and maintenance including effects on mitogenesis, survival, fate determination, differentiation, and migration. Using a conditionally immortalized rat hippocampal cell line, H19-7, and primary hippocampal cultures, we now demonstrate that FGF2 treatment differentially regulates members of the tumor necrosis factor (TNF) superfamily of death domain receptors and their ligands. H19-7 cells transferred from serum to defined (N2) medium undergo apoptosis by a Fas-dependent mechanism similar to primary neurons. In contrast, H19-7 cells treated with FGF undergo apoptosis by a Fas-independent mechanism. FGF suppresses the Fas death pathway but also induces apoptosis by activation of a TNFalpha death pathway in both H19-7 and hippocampal progenitor cells. Expression of the TNF receptor 1 (TNFR1) or TNFR2 in H19-7 cells is sufficient to sensitize the cells to TNFalpha, similar to the effects of FGF. Because TNFalpha can be either proapoptotic or antiapoptotic, these results provide an explanation for the divergent trophic effects of FGF2 treatment and the observation that multiple trophic inputs are required for the survival of specific neurons.

Genetics of Chlamydomonas reinhardtii diploids. I. Isolation and characterization and meiotic segregation pattern of a homozygous diploid.

A strain of Chlamydomonas reinhardtii has been investigated which, when mated with known wild-types, produces very few viable germination products and transmits its Mendelian markers to more than half of those products. Cytogenetic observations, fluorometric measurements of DNA and genetic data all suggest that the strain, d mt-ery-M3a sr-u-1 is a stable homozygous diploid. This strain has twice as many nuclear chromatin bodies at metaphase and twice as much DNA as its haploid progenitor, and the phenotypes of its meiotic progeny are consistent with predictions based on triploid meiosis. Data from crosses involving d mt-ery-M3a sr-u-1 and from crosses involving hybrid diploids indicate that the frequency of second division segregation increases in triploid zygotes and that mitotic segregation following triploid meiosis is a frequent event which may more often result from mitotic recombination than from chromosome loss.

Genetics of Chlamydomonas reinhardtii diploids. II. The effects of diploidy and aneuploidy on the transmission of non-Mendelian markers.

The transmission of two non-Mendelian drug resistance markers has been studied in crosses of Chlamydomonas reinhardtii involving diploids and aneuploids with different mating type genotypes. Under normal laboratory conditions for gametogenesis, mating and zygote maturation, the transmission pattern of the non-Mendelian markers sr-u-1 (resistance to streptomycin) and spr-u-1-27-3 (resistance to spectinomycin) is primarily determined by the mating type genotypes of the parental cells. Our results confirm and expand an earlier observation suggesting that an apparent codominant function of the female (mt+) allele in regulating chloroplast gene transmission in meiosis appears to be distinct and separate from its recessive function in regulating mating behavior. The chloroplast DNA complement (as indexed by the number of extranuclear DNA-containing bodies) may exert a secondary effect on the transmission of these markers. Within a mating type group (mt+/mt- or mt-/mt-) a cell line with more chloroplast DNA tended to transmit its non-Mendelian markers more frequently than a cell line with less chloroplast DNA.

Differences in burst morphology among baboon species.

Baboon species differ markedly in the proportions of fetal hemoglobin (HbF) they produce in response to hemopoietic stress. Bone marrow erythroid progenitor cells from untreated and stressed baboons of three species were cultured to determine if differences in number, size, or other characteristics of the colonies and bursts could be correlated with the HbF response. BFU-E from adult Papio cynocephalus produced high proportions of macroscopic, well-hemo-globinized bursts, whereas those from P. anubis and P. papio produced only small, moderately hemoglobinized bursts. The species-specific differences in burst characteristics did not correlate with the in vivo HbF response to stress and they were not altered by variations in culture conditions. However, bone marrow BFU-E from P. anubis and P. cynocephalus fetuses produced similar bursts, suggesting developmental regulation of progenitor cell growth patterns. The proportions of macroscopic bursts were reduced in P. cynocephalus animals undergoing hemopoietic stress, suggesting that culture is a more severe erythropoietic stress for P. anubis and P. papio BFU-E than for P. cynocephalus BFU-E.

Insulin gene expression in immortalized rat hippocampal and pheochromocytoma-12 cell lines.

Employing reverse transcription-polymerase chain reaction and clonal cell lines derived by retroviral transduction of the temperature sensitive simian virus 40 large T-antigen into dispersed rat embryonic hippocampal cells, we detected the ancestral gene-insulin II mRNA in three progenitor subcloned cell lines. These cell lines upon differentiation are known to express markers indicative of commitment to either neuronal (H19-7; NF + , GFAP -), glial (H19-5; GFAP +, NF -), or bipotential (H583-5, NF +, GFAP + ) lineages. No duplicated, i.e., insulin I gene expression, was observed in any of the three cell lines. Induction of differentiation was associated with the persistence of insulin II mRNA and in the cells expressing a neuronal phenotype (H19-7; NF +, GFAP -) a relative doubling in insulin II mRNA level was present (P < 0.05). Minimal cellular insulin immunoreactivity was detected only in a subpopulation of cells with a differentiated neuronal phenotype. Radioimmunoassayable insulin peptide in the H19-7 cellular conditioned medium revealed a 5-fold increase in the differentiated state. In contrast, peripheral sympathetic PC-12 neuronal cells both in the undifferentiated and nerve growth factor-driven differentiated states, failed to express both insulin I and insulin II genes. We conclude that insulin II is expressed by cultured rat hippocampal clonal cell lines, and not by the peripheral sympathetic PC-12 neuronal cell line.

Conditional immortalization of neuronal cells from postmitotic cultures and adult CNS.

To determine whether postmitotic neurons can be immortalized by oncogenic transduction, we used two approaches involving conditional expression of a temperature-sensitive SV40 large T antigen (Tts). Initially, Tts was introduced into E17 rat embryonal hippocampal cells that were then cultured at the non-permissive temperature to enrich for postmitotic pyramidal neurons, and subsequently cloned at the permissive temperature. One clonal line (HMR10-3) expressed neuron-specific proteins upon differentiation, was capable of generating action potentials, and formed synapses with primary rat neurons in co-culture. Replating of these postmitotic cells at the permissive temperature resulted in reversible loss of neurofilament expression. Conditionally immortalized cell lines were also generated from the brain of an adult mouse carrying an inducible Tts transgene. These lines proliferated in a T antigen-dependent manner and expressed neuron-specific proteins upon differentiation at the non-permissive temperature. These results suggest that postmitotic neurons can be induced to enter the cell cycle without losing their commitment to a neuronal lineage.

Expression of glucocorticoid and mineralocorticoid receptors in an immortalized hippocampal neuronal cell line.

A clonal cell line of rat embryonic hippocampal origin (H19-7) has been examined for the expression of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR). H19-7 cells grown at 33 degrees C continue to divide, however when grown at 39 degrees C in reduced levels of serum the cells undergo morphological differentiation and express neuronal properties. Immunocytochemistry demonstrated that H19-7 cells express both MR and GR when grown at either 33 degrees C or 39 degrees C. GR mRNA is readily detected in H19-7 cells by RNase protection assay. MR mRNA levels in H19-7 cells are too low to detect by RNase protection, but can be detected by RT-PCR. RT-PCR also demonstrated that H19-7 cells express more GR mRNA than primary hippocampal neurons. Since previous studies have shown that the level of MR mRNA is higher than that of GR mRNA in hippocampal neurons, these studies suggest that H19-7 cells represent hippocampal neurons immortalized at an early stage when the MR system is not yet fully differentiated.

Expression of recessive Aprt- mutations in mouse CAK cells resulting from chromosome loss and duplication.

Karyotypes of recessive mutants at the autosomal adenine phosphoribosyltransferase (Aprt) locus in a clone of the near-diploid mouse CAK cell line have been analyzed. The Aprt located on chromosome 8. One copy of chromosome 8 was morphologically abnormal in the parental clone (CAK-B3-Toyr13) from which Aprt- mutants were isolated. Among 22 mutants, there were ten in which one copy of chromosome 8 had been lost. Four of these were monosomic, and in the others duplication of the remaining homolog had occurred. These findings indicate that newly induced recessive mutations in cultured mammalian cells can be expressed as the result of loss of one chromosome carrying a wild-type allele with or without duplication of the homolog carrying the mutant allele. Loss and duplication would not be detected in cell lines lacking morphologically marked chromosomes.

Chromosome segregation is frequently associated with the expression of recessive mutations in mouse cells.

The genes coding for adenosine kinase (ADK; ATP:adenosine 5'-phosphotransferase, EC 2.7.1.20) and esterase-10 (ES-10; carboxylesterase, carboxylic-ester hydrolase, EC 3.1.1.1) are both located on chromosome 14 in the mouse. The near-diploid mouse cell line CAK is heterozygous for two electrophoretic variants of ES-10. Recessive Adk- mutants of CAK have been isolated and analyzed for Es-10 phenotype and karyotypic abnormalities. Two classes of mutants were found with approximatley equal frequencies: those that remained heterozygous in the expression of Es-10 and those that expressed only one Es-10 allele. Of the mutants that lacked one form of ES-10, approximately half were missing most or all of one copy of chromosome 14; the other contained two copies of 14, frequently in the form of an isochromosome. There were no abnormalities of this chromosome found among the mutants that were Es-10 heterozygotes. These results suggest that the expression of an autosomal recessive mutation in near-diploid mouse cells is frequently associated with events that result in the segregation of a physically linked marker and part or all of a chromosome.

Activation of mitogen-activated protein kinase by epidermal growth factor in hippocampal neurons and neuronal cell lines.

Epidermal growth factor (EGF) functions in a bimodal capacity in the nervous system, acting as a mitogen in neuronal stem cells and a neurotrophic factor in differentiated adult neurons. Thus, it is likely that EGF signal transduction, as well as receptor expression, differs among various cell types and possibly in the same cell type at different stages of development. We used hippocampal neuronal cell lines capable of terminal differentiation to investigate changes in EGF receptor expression, DNA synthesis, and stimulation of mitogen-activated protein (MAP) kinase by EGF before and after differentiation. H19-7, the line that was most representative of hippocampal neurons, was mitogenically responsive to EGF only before differentiation and increased in EGF binding after differentiation. MAP kinase was stimulated by EGF in both undifferentiated and differentiated cells, as well as in primary hippocampal cultures treated with either EGF or glutamate. These results indicate that the activation of MAP kinase by EGF is an early signaling event in both mitotic and postmitotic neuronal cells. Furthermore, these studies demonstrate the usefulness of hippocampal cell lines as a homogeneous neuronal system for studies of EGF signaling or other receptor signaling mechanisms in the brain.

A homeodomain protein binds to gamma-globin gene regulatory sequences.

Developmental regulation of gamma-globin gene expression probably occurs through developmental-stage-specific trans-acting factors able to promote the interaction of enhancer elements located in the far upstream locus control region with regulatory elements in the gamma gene promoters and 3' A gamma enhancer located in close proximity to the genes. We have detected a nuclear protein in K562 and baboon fetal bone marrow nuclear extracts capable of binding to A+T-rich sequences in the locus control region, gamma gene promoter, and 3' A gamma enhancer. SDS/polyacrylamide gel analysis of the purified K562 binding activity revealed a single protein of 87 kDa. A K562 cDNA clone was isolated encoding a beta-galactosidase fusion protein with a DNA binding specificity identical to that of the K562/fetal bone marrow nuclear protein. The cDNA clone encodes a homeodomain homologous to the Drosophila antennapedia protein.

Homologous recombination between plasmids in mammalian cells can be enhanced by treatment of input DNA.

We have used the eukaryotic-prokaryotic shuttle vector pSV2Neo to demonstrate that cultured mammalian somatic cells have the enzymatic machinery to mediate homologous recombination and that the frequency of this recombination can be enhanced by pretreatment of the input DNA. Two nonoverlapping deletion mutants of pSV2Neo were constructed, each affecting the bacterial aminoglycoside 3'-phosphorylase gene (the neo gene), which confers resistance to aminoglycoside antibiotics on bacteria and resistance to the antibiotic G418 on mammalian cells. Mammalian cells transfected with either deletion plasmid alone yield no G418 -resistant colonies. Cells cotransfected with both deletion plasmids yield G418 -resistant colonies with high frequency. We show that these resistant colonies result from recombination involving homologous crossing-over or gene conversion between the deletion plasmids by rescuing from the resistant cells both types of reciprocal recombinant, full-length plasmids, and doubly deleted plasmids. Cutting one of the input plasmids to generate a double-stranded gap in the neo gene considerably enhances the frequency of homologous recombination within the gene. This suggests that targeting exogenous DNA to specific sites in mammalian chromosomes could be facilitated by suitable pretreatment of the DNA.

Apoptosis induced by differentiation or serum deprivation in an immortalized central nervous system neuronal cell line.

To characterize the nature of programmed cell death (PCD) induced in neuronal cells during development, three regulators of apoptosis were investigated: one, the bcl-2-related genes, modulate cell survival, and the other two, the interleukin-1 beta converting enzyme (ICE)-related enzymes and the tumor suppressor protein p53, have been implicated as mediators of apoptosis. These regulators were studied in H19-7 cells, an SV40 Tts-immortalized rat hippocampal neuronal cell line that can be differentiated with basic fibroblast growth factor at the nonpermissive temperature, resulting in a rapid attrition of cells by apoptosis. PCD occurred by two mechanisms in H19-7 cells: The first was initiated by removal of serum from undifferentiated cells, and the second was a consequence of neuronal differentiation. In differentiated H19-7 cells, the survival time was increased by both human bcl-2 and bcl-xL, and this could be reversed by bcl-xs. Addition of a peptide inhibitor of the ICE enzyme family to H19-7 cells resulted in a transient protection against differentiation-associated apoptosis, whereas no further protection was observed in the BCL-2- or BCL-XL-expressing cells. Shifting the differentiated cells to 33 degrees C to inactivate p53 did not significantly affect the apoptotic process, indicating that apoptosis induced by neuronal differentiation is not dependent on the continued presence of p53. By contrast, in undifferentiated cells, cell loss induced by transfer to serum-free media occurred more rapidly on inactivation of large T, consistent with p53 involvement. This medium-induced decrease in cell survival could not be rescued by the ICE inhibitor but was partially rescued by BCL-2 or BCL-XL. Furthermore, studies involving expression of BCL-2 and BCL-XL alone or together revealed differences in the survival dependent on the cellular environment. These results suggest that apoptosis of neuronal cells occurs by at least two processes: one in undifferentiated cells initiated by removal of serum and one linked to differentiation. The data implicate the ICE enzyme family but not p53 in apoptosis induced by differentiation and demonstrate that either BCL-2 or BCL-XL can prolong the survival of differentiated neuronal cells.