The destruction box is involved in the degradation of the NTE family proteins by the proteasome.

Neuropathy target esterase (NTE) and NTE-related esterase (NRE) are endoplasmic reticulum (ER) membrane-anchored proteins belonging to the NTE protein family. NTE and NRE are degraded by macroautophagy and by the ubiquitin-proteasome pathway. However, the regulation of NTE and NRE by proteasome has not been well understood. Western blotting showed that the deletion of the regulatory region of NTE and NRE led to protein accumulation compared with that of the corresponding wild-type proteins. Further, deletion and site-directed mutagenesis experiments demonstrated that the destruction (D) box was required for the proteasomal degradation of NTE and NRE. However, unlike the deletion of the regulatory region, the deletion of the D box did not affect the subcellular localisation of NTE or NRE or disrupt the ER. Moreover, the deletion of the D box or the regulatory region of NTE has similar inhibitory effects on cell growth, which are greater than those produced by the full-length NTE. Here, for the first time, we show that the D box is involved in the regulation of NTE family proteins by the proteasome but not in their subcellular localisation. In addition, these results suggest that the NTE overexpression-mediated inhibition of cell growth is related to active protein levels but not to its ER disruption effect.