In neural development, bone morphogenetic proteins (BMPs) restrict neuronal differentiation, thereby promoting the maintenance of progenitor cells or even inducing astrocytogenesis. We report that exposure of neuroendocrine lung carcinoma cells to BMP-2 leads to a rapid decline in steady-state levels of Mash1 protein and some neuron-specific markers. BMP-2 induces a post-transcriptional decrease in Mash1 levels through enhanced degradation. We demonstrate that Mash1 protein stability is tightly regulated by the E47/Id1 expression ratio. Transient induction of Id1 by BMP-2 negatively correlates with Mash1 levels. Furthermore, an ectopic increase in Id1 levels is sufficient to induce degradation of either ectopic or endogenous Mash1, whereas expression of Mash1 in Id1-deficient cells or overexpression of E47 makes Mash1 levels refractory to the addition of BMP-2. Furthermore, we show that the E47/Id1 expression ratio also regulates CK2-mediated phosphorylation of Mash1 on Ser152, which increases interaction of Mash1-E47 heterodimers. We propose a novel mechanism in which the balance between Id and E protein levels regulates not only the transcriptional function but also protein stability of the neurogenic bHLH transcription factor Mash1.

No abstract

No abstract

Patients with paraneoplastic cerebellar degeneration and Hodgkin's disease develop autoantibodies (Tr-Ab) that immunoreact with the cytoplasm of the Purkinje cells and produce a characteristic punctate pattern in the molecular layer of the cerebellum. In the present study, we analyzed the structures of the adult rat cerebellar cortex identified by Tr-Ab and the expression of the antigen recognized by Tr-Ab in the developing rat brain. By laser confocal microscopy and immunoelectron microscopy, Tr-Ab immunoreactivity was found localized in the cytosol and outer surface of the endoplasmic reticulum of the perikarya of neurons of the molecular layer and the cell body and dendrites of Purkinje cells without a particular concentration in dendritic spines. Tr-Ab reactivity was more widespread in the developing rat brain. Tr-Ab labeling of Purkinje cells was already observed at P0 (day of birth). The staining of the molecular layer followed the development of the dendritic tree. The internal and inner level of the external granule cell layer were labeled with Tr-Ab with a dotted pattern that became almost negative by the 2nd postnatal week. The staining probably corresponded to granule cells as suggested by the positive Tr-Ab labeling of cultures of embryonic granule neurons. The present findings suggest that the antigen recognized by Tr-Ab appears early and is widely expressed in the developing rat brain. In the adult cerebellum, the antigen is localized in the cell body and dendrites of the Purkinje cells but is not concentrated in the dendritic spines.