Protein tyrosine phosphatases are up-regulated and participate in cell death induced by polyglutamine expansion

Polyglutamine expansion is the cause of several neurodegenerative diseases. An in vitro model of polyglutamine-induced neuronal cell death was developed using truncated mutant huntingtin (Htt) and PC12 cells. Cell death was specifically observed in cells expressing a truncated mutant huntingtin-green fluorescence protein (GFP) fusion protein with 118 glutamine repeats (Gln(118)), as demonstrated by the release of lactate dehydrogenase (LDH). To gain further insights into the mechanisms of polyglutamine expansion-induced cell death, the Affymetrix rat genome array U34A was used to investigate gene expression changes associated with polyglutamine-mediated protein aggregation and cell death. Among the up-regulated genes, the increase of four protein tyrosine phosphatases (PTPs) was further confirmed by real-time quantitative reverse transcription PCR. Protein expression of mitogen activated protein (MAP) kinase phosphatase 1 (MKP1) was also increased as demonstrated by Western blot. Furthermore, phosphorylation of MAP kinase extracellular signal-regulated kinase 1/2 (ERK1/2) was substantially reduced in association with protein aggregation, and two general PTP inhibitors, sodium orthovanadate and bpV(pic), dramatically rescued the cells from polyglutamine-induced cell death. These results suggest that one or more of the PTPs are involved in the polyglutamine-induced cell death.