YY1-dependent transcriptional regulation of the human GDAP1 gene.

Charcot-Marie-Tooth disease (CMT) is a heritable neurodegenerative condition, some types of which (notably CMT4A) are caused by mutations in the GDAP1 gene that encodes a protein of unknown molecular function implicated in regulation of mitochondrial fission. Here we present for the first time a functional analysis of the GDAP1 gene promoter which we found to be transcriptionally regulated by YY1, a broadly studied factor that seems to be involved in regulating many of the same cellular phenomena as GDAP1. We show that GDAP1 is broadly expressed in cancer cell lines of different tissue origin, contrasting with the restricted neuronal distribution reported by some authors. There is a consensus YY1 binding site in the GDAP1 core promoter which we show to be functional in both in vitro binding assays and in living cells. Overexpression of YY1 activated the GDAP1 promoter in a reporter gene system as well as increased the level of endogenous mRNA. RNAi-mediated knockdown of YY1 in HEK293 cells led to decreased GDAP1 expression. While YY1 is known to exert both positive and negative regulatory influences on nuclear-encoded mitochondrial proteins, as well as on neurodegeneration-related genes, in all cell lines we studied (including neuroblastoma) the effect of YY1 on GDAP1 expression is activatory. This leads to interesting conclusions about the possible clinical role of this interaction and suggests a broader regulatory network.