Jr. Hwang et I. Lindberg, Inactivation of the 7B2 inhibitory CT peptide depends on a functional furin cleavage site, J NEUROCHEM, 79(2), 2001, pp. 437-444
The eukaryotic subtilisin prohormone convertase 2 (PC2) is known to require
in vivo exposure to the neuroendocrine protein 7B2 in order to produce an
enzymatically active species capable of proteolytic action on prohormone su
bstrates. In the present study, we examined the role of the pentabasic site
within 27-kDa 7B2 in this process. We prepared two His-tagged recombinant
7B2s by overexpression in bacteria: 7B2-Ser-Ser (SS), with an inactivating
mutation in the CT peptide from Lys171-Lys172 (KK) to SS, rendering the CT
peptide non-inhibitory; blockade-SS, a double mutant of both the CT peptide
as well as of the pentabasic furin cleavage site. These purified proteins
were used in a cell-free proPC2 activation assay. Both 7B2-SS as well as bl
ockade-SS were able to facilitate the activation of proPC2 (as judged by ef
ficient production of enzyme activity), suggesting that cleavage at the fur
in site is not required for 7B2s lacking inhibitory CT peptides. Plasmids e
ncoding proPC2 and various 7B2s were transiently transfected into human emb
ryonic kidney (HEK293) cells and PC2 enzymatic activity and CT forms in eac
h overnight conditioned medium were measured. Cells transfected with proPC2
and wild-type 7B2 secreted CT peptide cleavage products, but cells transfe
cted with proPC2 and the blockade mutant overwhelmingly secreted intact, 27
-kDa, blockaded 7B2. Medium obtained from HEK293 cells transfected with pro
PC2 and either wild-type 7B2, 7B2-SS, or blockade-SS exhibited PC2 activity
, but medium from cells expressing the 7B2 blockade mutant did not. We conc
lude that cleavage at the 7B2 furin consensus site is required to produce P
C2 capable of efficient proteolytic inactivation of the CT peptide.