Faculty Bibliography

Peptide growth factors such as the neurotrophins and fibroblast growth factors have potent effects on synaptic transmission, development, and cell survival. We report that chronic (hours) treatment with basic fibroblast growth factor (FGF-2) potentiates Ca(2+)-dependent N-methyl-D-aspartate (NMDA) receptor inactivation in cultured hippocampal neurons. This effect is specific for the NMDA-subtype of ionotropic glutamate receptor and FGF-2. The potentiated inactivation requires ongoing protein synthesis during growth factor treatment and the activity of protein phosphatase 2B (PP2B or calcineurin) during agonist application. These results suggest a mechanism by which FGF-2 receptor signaling may regulate neuronal survival and synaptic plasticity

PC12 cells differentiate in response to nerve growth factor from a chromaffin cell to a sympathetic neuronal phenotype. Wnt-1 is a secreted signaling factor required for development of mammalian midbrain and cerebellum. PC12 cells transformed by Wnt-1 fail to express several differentiation-specific genes in response to nerve growth factor. We have previously shown that HES-1, a negative regulator of neuronal differentiation, is increased in Wnt-1/PC12 cells (P. S. Issack and E. B. Ziff. Altered expression of helix-loop-helix transcriptional regulators and cyclin D1 in Wnt-1-transformed PC12 cells. Cell Growth & Differ., 9: 837-845). Here, we show that the HES-1 promoter is more active in Wnt-1/PC12 cells relative to PC12 and that the binding sites for the transcription factor RBP-J kappa contribute to this induction. We also identify two additional promoter elements required for elevated HES-1 expression. One element binds Wnt-1-induced protein complexes in a sequence-specific manner. Identification of Wnt-1 responsive elements in potential target genes may provide clues to nuclear pathways regulated by Wnt-1

The tyrosine hydroxylase (TH) gene encodes the rate-limiting enzyme in the biosynthesis of catecholamines. We have investigated the roles of two elements of the TH promoter, the TH-'Fat Specific Element' (TH-FSE) which binds the Fos-Jun complex, and the cAMP Response Element (CRE), which binds CREB and the co-activator protein, CREB Binding Protein (CBP) in regulating TH gene transcription. In PC12 cells, the TH-FSE was required for induction by NGF while the CRE was required for induction by cAMP. We show that both elements can function independently and contribute strongly to TH promoter basal activity in PC12 cells. We employed transient expression in the F9 teratocarcinoma cell line to vary experimentally the levels of the nuclear regulators implicated in TH control by the PC12 studies. In F9 cells, the TH promoter was strongly activated by Fos and Jun, and by PKA-stimulated CREB protein. In F9 and NIH3T3 cells, CBP, a co-activator which targets Fos-Jun and PKA-stimulated CREB, also induced the TH promoter. Immunohistochemical studies in rat brain regions enriched in dopaminergic neurons, including the midbrain and olfactory bulb (OB), suggest that Fos-Jun and CREB make differential contributions to TH gene activity in different tissues. Whereas changes in Fos protein levels parallel decreases in TH protein upon olfactory deprivation, CBP levels remain unchanged. This suggests that CRE-associated factors, including CBP, are not major regulators in the OB. In contrast, the presence of CREB and the absence of Fos immunoreactivity in midbrain dopaminergic cells suggests that the CRE is the primary regulator in this region

Nerve growth factor induces PC12 cells to differentiate from a chromaffin cell to a sympathetic neuronal phenotype. In contrast, PC12 cells, which stably express Wnt-1, a secreted signaling factor required for development of mammalian midbrain and cerebellum, fail to express differentiation-specific genes in response to nerve growth factor. Analysis of factors binding to E box-containing regulatory elements of the terminal differentiation gene encoding peripherin suggested a differentiation-specific control of expression of helix-loop-helix transcriptional regulators. Specifically, the MASH-1 (mammalian achaete-scute homologue) helix-loop-helix transcription factor, which plays a positive role in neuronal differentiation, is reduced in Wnt-1/PC12 cells, and HES-1, a negative regulator of MASH-1, is increased. These data suggest that the differentiation block may result from induction of HES-1. Wnt-1/PC12 cells also proliferate more rapidly and express increased levels of cyclin D1. Thus, Wnt-1 may block the differentiation and enhance the proliferation of PC12 cells by activating HES-1 and cyclin D1 and repressing MASH-1