Alcohol-Mediated Missplicing of Mcl-1 Pre-mRNA is Involved in Neurotoxicity.

BACKGROUND: Heavy and chronic ethanol (EtOH) exposure can cause significant structural and functional damage to the adult brain. The most devastating consequence of EtOH exposure is the neurotoxicity associated with the depletion of neurons. Regulation of splice variants in the brain can modulate protein functions, which may ultimately affect behaviors associated with alcohol dependence and EtOH-mediated neurotoxicity. As alcohol consumption is associated with neurotoxicity, it is possible that altered splicing of survival and pro-survival factors during the development of alcoholism may contribute to the neurotoxicity.

METHODS: Primary human neurons and a neuroblastoma cell line were exposed to different concentrations of EtOH for various time periods. Cell viability and neuronal marker expression were analyzed by MTT assay and immunoblotting, respectively. Effect of EtOH exposure on splicing regulatory protein expression and alternative splicing of candidate genes was analyzed by a biochemical approach. Transcriptional activity of serine/arginine-rich splicing factor 1 (SRSF1) gene was determined by reporter gene analysis.

RESULTS: Our results suggest that EtOH exposure to neuronal cells at 25 mM and higher concentrations are detrimental. In addition, EtOH exposure caused a dramatic reduction in SRSF1 expression levels. Furthermore, EtOH exposure led to pre-mRNA missplicing of Mcl-1, a pro-survival member of the Bcl-2 family, by down-regulating the expression levels of SRSF1. Moreover, ectopic expression of both SRSF1 and Mcl-1L isoform was able to recover EtOH-mediated neurotoxicity.

CONCLUSIONS: Our results suggest that EtOH exposure can lead to pre-mRNA missplicing of Mcl-1 in neuronal cells. Our results indicate that EtOH exposure of neurons leads to a decrease in the ratio of Mcl-1L/Mcl-1S by favoring pro-apoptotic Mcl-1S splicing over anti-apoptotic Mcl-1L isoform suggesting that Mcl-1S may play a crucial role in neurotoxicity associated with alcohol consumption.