The Production of 53–55-kDa Isoforms Is Not Required for Ratl-Histidine Decarboxylase Activity

Abstract

Post-translational processing of the histamine-producing enzyme, L-histidine decarboxylase (HDC), leads to the formation of multiple carboxyl-truncated isoforms. Nevertheless, it has been widely reported that the mature catalytically active dimer is dependent specifically on the production of carboxyl-truncated 53-55-kDa monomers. Here we use transiently transfected COS-7 cells to study the properties of carboxyl-truncated rat HDC isoforms in the 52-58-kDa size range. Amino acid sequences important for the production of a 55-kDa HDC isoform were identified by successive truncations through amino acids 502, 503, and 504. Mutating this sequence in the full-length protein prevented the production of 55-kDa HDC but did not affect enzymatic activity. Further truncations to amino acid 472 generated an inactive 53-kDa HDC isoform that was degraded by the proteasome pathway. These results suggested that processed isoforms, apart from 53-55-kDa ones, contribute toward histamine biosynthesis in vivo. This was confirmed in physiological studies where regulated increases in HDC activity were associated with the expression of isoforms that were greater than 55 kDa in size. We provide evidence to show that regulation of HDC expression can be achieved by the differential production or differential stabilization of multiple enzyme isoforms.

Activation of Histidine Decarboxylase through Post-translational Cleavage by Caspase-9 in a Mouse Mastocytoma P-815

“…On the other hand, only 74-kDa form was detected in lipopolysaccharide-activated mouse macrophages and monomeric IgE-activated immature bone marrow-derived cultured mast cells, in both of which a large increase in histamine synthesis is observed (21,22). Other variants with intermediate sizes (58ϳ64-kDa) have also been reported in the stomach, fetal liver, and testis (18,23,24). These findings have highlighted the complexity in the regulation of enzyme activity and intracellular localization of HDC through the post-translational processing.…”

“…C-terminal 20-kDa region mediates the ER-targeting of HDC and the membrane-bound 74-kDa form possesses a lower activity than that of the truncated 54-kDa form in the cytosol. Fleming and Wang (18) demonstrated that rat 74-kDa form expressed in COS-7 cells is cleaved to multiple forms and that formation of the main 55-kDa form is prevented by mutations at the residues, Ser 502 , Lys 503 , and Asp 504 , whereas these mutations had no effects on the enzyme activity. However, this putative processing site was not found in the primary sequence of mouse and human HDC, and no processed forms were detected in COS-7 cells expressing mouse 74-kDa HDC (17).…”

Kruppel-like Factor 4 (KLF4) Represses Histidine Decarboxylase Gene Expression through an Upstream Sp1 Site and Downstream Gastrin Responsive Elements

“…tion occurs at both the transcriptional and post-translational levels, the latter by proteolytic processing through the ubiquitin-proteasome pathway (6,7).…”

H3Autoreceptors Modulate Histamine Synthesis through Calcium/Calmodulin- and cAMP-Dependent Protein Kinase Pathways

“…Further work will examine which sites were phosphorylated under our conditions as well as the kinetic parameters modified by CaMKII phosphorylation. It is generally accepted that carboxyl-terminal truncation of the full-length protein yields a catalytically active form of M r 55,000, whose properties are matched closely by 1/512 HDC (Taguchi et al, 1984;Joseph et al, 1990;Engel et al, 1996;Olmo et al, 2002;Rodriguez-Caso et al, 2003), although controversy about the size of the functional forms of HDC in vivo still exists (Dartsch et al, 1999;Fleming and Wang, 2003). On the other hand, CaMKII activation of HDC does not seem to require additional proteins, because we can increase its activity in vitro using purified enzymes.…”

“…These neurons are characterized by the presence of the en-zyme-synthesizing histamine histidine decarboxylase (HDC). HDC is a pyridoxal-5Ј-phosphate-dependent decarboxylase translated as a 74-kDa precursor that undergoes carboxylterminal truncation to yield the active forms of the enzyme (Joseph et al, 1990;Dartsch et al, 1999;Fleming and Wang, 2003;Rodriguez-Caso et al, 2003). In a previous work, we showed that histamine synthesis can be stimulated by the adenylate cyclase/protein kinase A pathway in nerve endings, an effect that is inhibited by H 3 receptors (GomezRamirez et al, 2002).…”