The CAG repeat in SCA12 functions as a cis element to up-regulate PPP2R2B expression

Abstract

PPP2R2B, a protein widely expressed in neurons, regulates the protein phosphatase 2A (PP2A) activity for dephosphorylation of tau and other substrates. CAG repeat expansion at the 5'-end of the PPP2R2B gene causes autosomal dominant spinocerebellar ataxia type 12. In the present study, we investigated the roles of CAG repeats and flanking cis elements and the associated proteins in controlling PPP2R2B expression. Deletion/site-directed mutagenesis, in silico searches and cDNA overexpression revealed that CREB1 and SP1 bind to the conserved sequence upstream the CAG repeats to up-regulate PPP2R2B expression, whereas TFAP4 binds to the conserved sequence downstream the CAG repeats to down-regulate PPP2R2B expression. The binding of CREB1, SP1, and TFAP4 to the PPP2R2B promoter was further confirmed by DNA pull-down and ChIP-PCR assays. CAG repeats itself also function as a cis element to up-regulate PPP2R2B expression as AT repeat length has no effect on PPP2R2B expression. Together, our data provide evidence that CREB1, SP1, and TFAP4 play roles in modulating PPP2R2B expression, thus offering a mechanism of regulating PP2A activity as the treatment of neurodegenerative diseases associated with abnormal PP2A activity.

Neuropathology and Cellular Pathogenesis of Spinocerebellar Ataxia Type 12

“…Similar results were observed using a CAT reporter assay (data not shown). These results are consistent with previous findings in these neuroblastoma cells . The same effect of increasing repeat length on reporter activity was evident in primary cortical neurons (Fig.…”

“…First, we confirmed the strong promoter activity of the PPP2R2B repeat region previously reported in human neuroblastoma lines . In LA‐N‐1 (Fig.…”

“…The pathogenic pathways involved in SCA12 remain unknown. One possibility, based on the location of the repeat within a predicted PPP2R2B promoter, is that repeat length may influence the expression level of the PPP2R2B isoform that encodes Bβ1, a phenomenon also observed at other repeat loci . Here, we describe, for the first time, neuropathology of an SCA12 brain, and we provide evidence that this neuropathology may derive from an effect of the SCA12 repeat expansion on Bβ1 expression …”

Dysregulation of the causative genes for hereditary parkinsonism in the midbrain in Parkinson's disease

“…Considerable evidence also suggests a loss‐of‐function mutation in which unstable repeat disorder genes are knocked out, which enhances cell death . Expanded CAG repeats in PPP2R2B are not translated, although they regulate the transcription of PPP2R2B . We could not find studies that investigated the relationship between PPP2R2B and dopaminergic neuronal death.…”

Consensus Paper: Pathological Mechanisms Underlying Neurodegeneration in Spinocerebellar Ataxias

“…Unique among spinocerebellar ataxias, SCA12 has been proposed to be caused by a brain-specific regulatory subunit (Bß2) of the protein phosphatase PP2A that upon cell stress is rapidly targeted to the outer mitochondrial membrane, where it promotes apoptosis by inducing Drp1- and Fis1-dependent mitochondrial fission [317]. The SCA12 mutation is a CAG repeat expansion in the PPP2R2B 5′ untranslated region, which functions as a cis promoter element that upregulates PPP2R2B expression [318]. Therefore, the disease process would originate from an abnormally increased activity of a pro-apoptotic protein, resulting in severe fragmentation of the mitochondrial network.…”