Reduced viability of neuronal cells after overexpression of protein histidine phosphatase

Protein histidine phosphatase (PHP) has just recently been discovered in eukaryotes and ATP-citrate lyase (ACL) was shown to be one of its substrates. Since ACL is crucial for cellular energy and fat metabolism we made an attempt to study the influence of PHP on cell viability. Using an adenoviral vector PHP was overexpressed in SN56 cholinergic murine neuroblastoma cells and in primary cultures of hippocampal neurons obtained from embryonic rats (E18). Overexpression of PHP in these cells caused a decrease in ACL activity and consequently impaired viability. To be sure that the reduced cellular viability was achieved by overexpression of PHP we also downregulated ACL in SN56 cells using RNAi-technology. Downregulation of ACL was harmful to the cells similar to what was observed upon overexpression of PHP. Taken together, it is concluded that overexpression of PHP results in increased dephosphorylation with concomitant inactivation of ACL, thus finally leading to cell damage.