Role for RFX Transcription Factors in Non-neuronal Cell-specific Inactivation of the Microtubule-associated Protein MAP1A Promoter

Abstract

Microtubule-associated protein MAP1A is expressed abundantly in mature neurons and is necessary for maintenance of neuronal morphology and localization of some molecules in association with the microtubulebased cytoskeleton. Previous studies indicated that its complementary expression together with MAP1B during nervous system development is regulated at the transcriptional level and that the mouse Map1A gene is transcribed under the control of 5 and intronic promoters. In this study, we investigated the regulatory mechanisms that govern the neuronal cell-specific activation of the MAP1A 5 promoter. We found that two regulatory factor for X box (RFX) binding sites in exon1 of both the mouse and human genes are important for effective transcriptional repression observed only in non-neuronal cells by reporter assays. Among RFX transcription factor family members, RFX1 and 3 mainly interact with repressive elements in vitro. Cotransfection studies indicated that RFX1, which is expressed ubiquitously, down-regulated the MAP1A 5 promoter activity in nonneuronal cells. Unexpectedly, RFX3, which is abundantly expressed in neuronal cells, down-regulated the transactivity as well, when it was expressed in nonneuronal cells. Both RFX1 and 3 did not down-regulate the transactivity in neuronal cells. These results suggest that RFX1 and 3 are pivotal factors in down-regulation of the MAP1A 5 promoter in non-neuronal cells. The cell type-specific down-regulation, however, does not depend simply on which RFX interacts with the elements, but seems to depend on underlying profound mechanisms.MAP1A is a high molecular weight MAP 1 that plays an important role in determining neuronal morphology and in determining the balance between plasticity and stability of neuritis (1, 2). MAP1A and 1B are particularly abundant filamentous MAPs in the brain and possess highly similar structures and functions in their stabilization of microtubule bands.Recent studies have demonstrated that MAP1A interacts with postsynaptic density-93, a membrane-associated guanylate kinase (3), and is involved in the general attachment of mRNA to the cytoskeleton (4). Thus, MAP1A seems to act not only in stabilizing microtubule bands but also in regulating the distribution of associated molecules as a linker between them and the microtuble-based cytoskeleton. MAP1B has been shown to link ␥-aminobutyric acid, type C receptors to microtubule (5), indicating that MAP1A and 1B anchor distinct target molecules to the cytoskeleton. The different expression patterns of MAP1A and 1B, which are transcriptionally regulated (6), also support the functional dichotomy of these two filamentous MAPs. MAP1B is the earliest MAP expressed during central nervous system development; it is most highly expressed during the postneonatal period, diminishing as the animal matures to adulthood (6 -9). In contrast, MAP1A expression increases continually during the postneonatal period and is maintained at a high level throughout adulthood (6, 8 -10).Multiple promoters, cell type-specific c...

The Transcription Factor Regulatory Factor X1 Increases the Expression of Neuronal Glutamate Transporter Type 3

“…However, up until now, there is no report documenting the effects of these RFXs on gene expression in cells of central nervous system origin. Based on the results generated from cell lines of different origins, it was concluded that RFX1 and RFX3 inhibited the expression of microtubule-associated protein 1A in cells of non-central nervous system origin, such as HeLa cells, but not in cells of central nervous system origin, such as TGW and Neruo2A cells (17). We showed that RFX1 enhanced the activity of EAAT3 promoter in C6 and SH-SY5Y cells and the expression of EAAT3 proteins in C6 cells.…”

“…Positively acting regulatory elements of the X-box after binding to RFXs have been shown in most of the viral promoters and in the promoter of interleukin-5 receptor ␣ chain (18,20). However, negatively acting regulatory elements of the X-box after binding to RFXs have been shown in the promoters for genes, such as proliferating cell nuclear antigen and microtubule-associated protein 1A (17,19). Thus, the functional change of a promoter by RFXs is context-dependent.…”

Analysis of xbx genes in C. elegans

“…We analyzed the 5′-UTR region of the human TUB gene and found two X-box-like sequences that perfectly match the C. elegans consensus: GTTGCC AT GGAAAC (-296) and GTTGCT AT AGTAAC (-339). Intriguingly, microtubule-associated protein 1A (MAP1A) can modify hearing defects in tubby mice (Ikeda et al, 2002), and its expression is regulated by RFX molecules (Nakayama et al, 2003). These observations suggest that the regulation of tubby pathways by RFX transcription factors can be conserved in evolution.…”

Regulatory Factor X Transcription Factors Control Musashi1 Transcription in Mouse Neural Stem/Progenitor Cells

“…We quantified the mRNA expression of Rfx in NS/PCs; Rfx1, 3, 4 and 7 were strongly expressed in NS/PCs. Rfx1 is ubiquitously expressed in brain, however, it transcriptionally represses neuronal marker MAP1A gene in non-neuronal cells but not in neuronal cells, and Rfx3 also shows repressive regulation of MAP1A in non-neuronal cells [54]. This indicates Rfx transcription factors function redundantly and in a cell type specific manner.…”