In vitro study of proteolytic degradation of rat histidine decarboxylase

Mammalian ornithine decarboxylase (ODC) is a very unstable protein which is degraded in an ATP-dependent manner by proteasome 26S, after making contac t with the regulatory protein antizyme. PEST regions are sequences describe d as signals for protein degradation. The C-terminal PEST region of mammali an ODC is essential for its degradation by proteasome 26S. Mammalian histid ine decarboxylase (HDC) is also a short-lived protein. The full primary seq uence of mammalian HDC contains PEST-regions at both the N- and C-termini. Rat ODC and different truncated and full versions of rat HDC were expressed in vitro. In vitro degradation of rat ODC and rat 1-512 HDC were compared. Like ODC, rat 1-512 HDC is degraded mainly by an ATP-dependent mechanism. However, antizyme has no effect on the degradation of 1-512 HDC. The use of the inhibitors MG-132 and lactacystine significantly inhibited the degrada tion of 1-512 HDC, suggesting that a ubiquitin-dependent, proteasome 26S pr oteolytic pathway is involved. Results obtained with the different modifica tions of rat HDC containing all three PEST regions (full version, 1-656 HDC ), only the N-terminal PEST region (1-512 HDC), or no PEST region (69-512 H DC), indicate that the N-terminal (1-69) fragment, but not the C-terminal f ragment, determines that the HDC protein is a proteasome substrate in vitro .