Vol.
4, 793-798,
October
1993
cell
Growth
& Differentiation
793
Transformation-sensitive
Localization
of
a-Protein
Kinase
C at Cell-Cell
Contacts
in Rat Renal
Proximal
Tubule
Epithelial
Cells1
Liqun Dong, James L. Stevens,
and Susan Jaken2
W. Alton
Jones cell
Science
center,
Inc.,
Lake Placid,
New
York 12946-1
099
Abstrad
Immunocytofluorescence
studies
were
used
to
compare
a-protein
kinase C (PKC)
localization
in primary
cultures
of renal
proximal
tubule
epithelial
cells
(RPTE) with
[lA-immortalized
and
SV4O-transformed
derivatives.
Both cytosolic and nuclear staining were apparent
in all
of the RPTE.
In primary
RPTE, Triton X-1 00-insoluble
a-PKC was also apparent
and was concentrated
in cell
jundions.
Cell
junction
a-PKC was diminished
in
El A-immortalized
and absent
from SV4O-transformed
RPTE, even
though
total
cellular
content
was not
decreased.
These
results emphasize
that subcellular
location
may
play
an
important
role
in
regulating
signal
transdudion
through
PKC-dependent
pathways.
Phorbol
ester
treatment
induced
cell membrane
ruffling
in
primary
RPTE, and a-PKC was redistributed
to
membrane
ruffles. However,
the redistributed
a-PKC
was Triton
soluble
and,
therefore,
was distind
from cell
junction
a-PKC.
The
loss of a-PKC
from cell
jundions
in
phorbol
ester-treated
and oncogene-altered
cells
suggests
that
there
are cellular
determinants
regulating
a-PKC association with
jundional
complexes.
Introdudion
PKC3 is a family
of phospholipid-dependent
kinases
impor-
tant
for
regulation
of cell
growth
and
differentiated
function
(1). The
family
can be divided
into
three
groups:
calcium-
dependent
(conventional
or Group
A) PKCs
(a,
f3, and y),
calcium-independent
(novel
or Group
B) PKCs
(, #{128},
rj, and
0), and calcium-
and phorbol
ester-independent
(Group
C)
PKCs
(i). The reasons
for PKC heterogeneity
are not yet fully
understood.
Presumably,
unique
isozyme
sequences
confer
isozyme-specific
properties
and
functions.
Phorbol
esters,
which
are potent
tumor
promoters,
bind
to and stimulate
the
catalytic
activity
o