De novo synthesis and posttranslational processing of L-histidine decarboxylase in mice

We purified L-histidine decarboxylase from mouse mastocytoma cells and cloned mouse HDC cDNA, and found that the primary translated product (74 kD) is posttranslationally processed in its C-terminal region to yield a native HDC subunit (53 kD). Recombinant 74-kD, but not 53-kD HDC species was present mainly in the particulate fraction of Sf9 cells. The particulate 74-kD recombinant HDC was cleaved by porcine pancreatic elastase, and a homodimer of a 53-kD subunit having the identical catalytic properties to those of native HDC was solubilized. The particulate HDC from mouse stomach was partially purified and it was solubilized by porcine pancreatic elastase to yield the 53-kD subunit of HDC. We identified endogenous proteolytic activity, which converts the particulate recombinant 74-kD HDC to the soluble 53-kD HDC in the supernatant of mouse stomach. In mastocytoma cells, we demonstrated that the induction of HDC activity and HDC mRNA synergistically occurred upon treatment with dexamethasone + TPA, and also with cAMP + Ca²⁺. On a genomic DNA cloning, we found that two upregulations occurred via the involvement of the regulatory elements binding to the sequences from -132 to -53 and -267 to -53, respectively.