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Pex3p-dependent peroxisomal biogenesis initiates in the endoplasmic reticulum of human fibroblasts.
[zellweger syndrome]
The
mechanisms
of
peroxisomal
biogenesis
remain
incompletely
understood
,
specially
regarding
the
role
of
the
endoplasmic
reticulum
(
ER
)
in
human
cells
,
where
genetic
disorders
of
peroxisome
biogenesis
lead
to
Zellweger
syndrome
(
ZS
)
.
The
Pex
3
p
peroxisomal
membrane
protein
(
PMP
)
required
for
early
steps
of
peroxisome
biogenesis
has
been
detected
in
the
ER
in
yeast
but
not
in
mammalian
cells
.
Here
,
we
show
that
Pex
3
p
-
GFP
expressed
in
a
new
ZS
cell
line
(
MR
)
,
which
lacks
peroxisomes
due
to
a
mutation
in
the
PEX
3
gene
,
localizes
first
in
the
ER
and
subsequently
in
newly
formed
peroxisomes
.
Pex
3
p
bearing
an
artificial
N-
glycosylation
site
shows
an
electrophoretic
shift
indicative
of
ER
targeting
while
en
route
to
preformed
peroxisomes
in
normal
fibroblast
.
A
signal
peptide
that
forces
its
entry
into
the
ER
does
not
eliminate
its
capability
to
drive
peroxisome
biogenesis
in
ZS
cells
.
Thus
,
Pex
3
p
is
able
to
drive
peroxisome
biogenesis
from
the
ER
and
its
ER
pathway
is
not
privative
of
ZS
cells
.
Cross-expression
experiments
of
Pex
3
p
in
GM
623
cells
lacking
Pex
16
p
or
Pex
16
p
in
MR
cells
lacking
Pex
3
p
,
showed
evidence
that
Pex
3
p
requires
Pex
16
p
for
ER
location
but
is
dispensable
for
the
ER
location
of
Pex
16
p
.
These
results
indicate
that
Pex
3
p
follows
the
ER-
to
-peroxisomal
route
in
mammalian
cells
and
provides
new
clues
to
understand
its
function
.