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*
Uppsala Genetic Center, Swedish University of Agricultural Sciences, and
Department of Medical Biochemistry and Microbiology, Biomedical Center, Uppsala University, Uppsala, Sweden
Expression of human MHC HLA-DRA class II gene can be
up-regulated in B cells by Ig cross-linking as well as by phorbol
esters such as 12-O-tetradecanoyl phorbol 13-acetate
(TPA). Induced DRA expression involves activation of
restricted protein kinase C (PKC) isoforms, resulting in activated
activator protein-1-dependent transcription. In this report expression
profiles and activation of PKC were analyzed in human Raji B
lymphoblastoid cells. Transient transfection analysis with target
plasmids containing either DRA promoter (wild-type or
mutated) or TPA response elements demonstrated that pretreatment with
the selective PKC inhibitor GF 109203X repressed TPA-mediated
activation. Western analysis performed on cellular fractions of resting
cells and of TPA-activated cells revealed abundant expression of
classical PKC-
(cPKC-), cPKC-ßII, and atypical PKC-
isoforms
and identified a sustained translocation of cPKC- and cPKC-ßII
from the cytosolic compartment to membranes. As expected, the
distribution of atypical PKC- was unaffected by TPA treatment and
displayed an even distribution between cytosol and membranes. This
finding was confirmed by immunofluorescence microscopy. The
TPA-mediated translocation of cPKC- and cPKC-ßII was not
influenced by pretreatment with GF 109203X. Finally, functional
activation and translocation of PKC were investigated with a selective
in vitro kinase assay. Together, these results show that activated
HLA-DRA expression in response to TPA treatment is
strictly dependent on PKC activation acting on the X2 box of the
DRA promoter and that selective inhibition of PKC
enzymatic activity does not influence subcellular localization of
expressed PKC isoenzymes. Thus, the translocation event per se occurs
independently of PKC activation in these cells.
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