Genetic variant in the HSPB1 promoter region impairs the HSP27 stress response

The 27 kDa heat shock protein 1 (HSP27) is a member of the ubiquitously expressed small heat shock protein family and has pleiotropic cytoprotective functions. Since HSP27 may act as a motor neuron survival factor, we analyzed the genetic contribution of the human HSPB1 gene (HSPB1) to the etiology of amyotrophic lateral sclerosis (ALS). In a cohort of sporadic ALS patients, we identified three rare genetic variations and one of which (c.-217T>C) targeted a conserved nucleotide of the Heat Shock Element (HSE) in the HSPB1 promoter. Since binding of Heat Shock Factor 1 (HSF1) to this HSE is essential for stress-induced transcription of HSPB1, we examined the effect of the c.-217C allele on transcriptional activity and HSF binding. The basal promoter activity of the HSPB1 c.-217C mutant allele decreased to 50% as compared to the wild-type promoter in neuronal and non-neuronal cells. Following heat shock, the HSE variant attenuated significantly the stress-related increase in transcription. Electrophoretic mobility shift assays demonstrated a dramatically reduced HSF-binding to the c.-217C mutant allele as compared to the c.-217T wild-type allele. In conclusion, our study underscores the importance of the c.-217T nucleotide for HSF binding and heat inducibility of HSPB1. Therefore, our study suggests that the functional HSPB1 variant may represent a genetic modifier in the pathogenesis of motor neuron disease; however, it is necessary to confirm this HSPB1 variant in additional ALS patients.