et a!., 1983;Klausneretal.,. 1983a,b). Iron transfer from the general circulation to the ...... Randall. RJ,. 1951. Protein measurements with the. Folin phenol reagent. .... NJ, Kester. HCM,. Noordeloos. PJ, Leijnse. B, 1979. Comparative studies on.
BIOLOGY
OF
35, 1227-12
REPRODUCTION
Transferrin
34 (1986)
Receptors Both
of Isolated Rat Seminiferous Rat and Human Transferrin
J. J.
PAULETTE
and
WAUBEN-PENRIS,’ HANS
Department
DER
of Cell
School
J.
GER
A. VAN
Tubules
Bind
STROUS,
DONK
Biology
of Medicine
University
of
Utrecht,
The
Utrecht
Netherlands
ABSTRACT The
binding
and
During the isolation Iron-saturated but
the
uptake and
and
dissociation
The affinity binding sites
of
rat
incubation iron-free
constant
and
human
transferrin
of the tubules, (apo-) transferrin is about
two
by
the blood-testis use the same
times
higher
for
isolated
rat
barrier binding
apotransferrin
of the receptors is equal for rat and human transferrin, but (2.6 x 1010 per 10 cm tubule length) than rat transferrin
seminiferous
remained sites on than
tubules
intact. the surface
for
was
studied.
the
tubules,
of
iron-saturated
human transferrin (1.1 x 1010 per
transferrin.
binds to more surface 10cm tubule length) at
0#{176}C. At 33#{176}Cequal numbers of human and rat transferrin molecules are taken up (about 8 x 1010) per 10 cm tubule length. The quantitative difference between 0#{176}C and 33#{176}Cis caused by the fact that at 33#{176}Creceptormediated endocytosis and recycling occur. As a consequence, both surface and intracellular transferrin receptors are
detected
at
330 C. The
dissociation
constants
are
not
temperature-dependent.
INTRODUCTION
Sertoli cells control within the seminiferous for spermatogenesis complexes between barrier
and
the (Fritz, Sertoli
exclude
electrolytes
from
tubule,
unless
Sertoli Gladwell,
cells
all the
they
composition tubule, which 1973). Tight cells create the
macromolecules luminal
pass
through
(Setchell and 1982; Russell
compartment the
role of transferrin in iron transport and to cells is well established (Baker and Morgan, Aisen and Listowsky, 1980; Perez-Infante and
several
Mather, 1982; Klausner require iron as a constituent and other heme-containing
of
physiological
junctional blood-testis and
cytoplasm
Wallace, 1972; and Peterson,
The delivery 1969;
of the fluid is important
the
of the
Waites 1985).
and In
conditions
et
al., 1983a). All cells of respiratory enzymes proteins; but, under
free
and Listowsky, function for
1980). Cells iron utilization,
(hemoglobin
synthesis)
iron
can
be toxic
expressing such as
and
syncytial
(Aisen
a specialized reticulocytes trophoblasts
addition to their function as a selective barrier, Sertoli cells contribute actively to the composition of the tubular content (Skinner and Griswold, 1980; Wright et al., 1981; Kissinger et a!., 1982; Waites and Gladwell, 1982). The glycoprotein transferrin is a major Sertoli cell product (Skinner and Griswold,
(iron transport across the placenta to the fetus), are exceptionally rich in transferrin receptors (Enns et al., 1981; Harding et a!., 1983). The transferrin receptor is also expressed in significant amounts in mitotically active cells, both normal and neoplastic
1980),
and
1981;
under 1982)
hormonal control and dependent on
(Perez-Infante
the
rate
et al.,
of
its synthesis
1982;
is reported
(Skinner and the surrounding Ritzen,
to
be
Griswold, germ cells
(Karin high
and
Mintz,
Klausner
1981;
et al.,
concentration
of
Trowbridge
1983a),
and
transferrin
and the
receptor
Omary,
presence
of a
molecules
on the cell surface is believed to be a specific marker for cellular proliferation (Larrick and Cresswell, 1979; Karin and Mintz, 1981; Sutherland et al., 1981; Trowbridge and Omary, 1981). Iron bound to transferrin (FeTf) enters the cell by receptor-mediated endocytosis. The iron then dis-
1983).
Accepted May 12, 1986. Received February 20, 1986. ‘Reprint requests: Paulette J. J. Wauben-Penris, Department of Cell Biology, School of Medicine, University of Utrecht, Nic. Beetsstraat 22, 3511 HG Utrecht, The Netherlands.
sociates from prelysosomal CURL 1227
transferrin, compartment
(Compartment
probably previously of
Uncoupling
in a low designated Receptor
pH as and
1228
WAUBEN-PENRIS
Ligand) Yamashiro unknown
(Ciechanover et al., way to
Listowski,
1980;
ferrin recycles
(apoTf), back
et al., 1983; Geuze et al., 1983; 1984), and is delivered in a yet iron storage proteins (Aisen and Klausner
et
the
medium
to
and
Mintz,
1981;
a!.,
1983;Klausneretal.,
be reutilized
1983b).
iron
et al.,
carrier
Bucks,
(Karin
Harding
et
1983a,b). from be iron
cross
the
the general a continuous is lost from
pool.
To
taken ported
up by the Sertoli cells through the cytoplasm
blood-testis
germ
cells.
which
the
There
are
several
seminiferous It could
barrier,
possible
tubules be
that
iron
must
iron,
be
transto the
mechanisms
could
accomplish
once
delivered
stages
review, possibility
see
Sertoli transferrin niferous
cells,
of
spermatogenic
by this
(for
are
be internalized round spermatids
further secreted Evidence
transported by Sertoli into the lumen of the exists that transferrin
by pachytene (Holmes et al.,
by using
and
lodo-beads
IL).
rat
transferrin
(Pierce
Unbound
fungizone, amino Scotland)
Darmstadt,
Chemical
was
125
mM
L-glutamin
acids, and
West
15
laboratory a
cell semican
spermatocytes 1983; Steinberger
MO),
and et
a!.,
(2
vitamins NaHCO3
Germany)
HEPES
removed
mM),
non-
(all from (0.85 g/l,
and
buffered
(Merck).
were of the highest available Male Wistar rats were
Russell and Peterson, 1985). Another is that iron ions, after being released in the
and tubule.
Louis,
Rockford,
streptomycin,
with
to the
cells
England)
Company,
essential Paisley,
Sertoli cells via serum diferric-transferrin and transferrin receptors, proceeds to the germ cells by gapjunctions that exist between Sertoli cells and some maturation
(St.
by gel filtration through a Sephadex G-25 column (Pharmacia, Uppsala, Sweden). Incubation medium was Eagles Minimum Essential Medium (MEM), supplemented with penicillin,
circulation to the process because the testicular iron
at the basal side, and forwarded
Co.
from Jackson Laboratories (Avondale, PA). These were made iron-free according to Aisen (1966) or were saturated with iron according to Klausner et al. (1983b). Proteins were iodiated with 125 I-Na (Amersham,
Apotrans-
1983;
AL.
Chemical
transferrin receptor, and is released into
as an
Ciechanover
Iron transfer germ cells must sperm-associated
transport.
al.,
bound to the to the cell surface
ET
All
Gibco, Merck,
to
other
quality. kept under
pH
7.4
chemicals standardized
conditions.
Isolation and Incubation Testes incubated
from with
of Seminiferous
mature 10 mg
rats were collagenase
decapsulated and (CLS II; Worthing-
ton, Malvern, PA) in 20 ml Hanks’ Solution (HBSS) for 5 mm in a shaking 33#{176}C(150
cycles
three
times
with
and
incubated
per
mm).
HBSS, for
The
teased
mm
30
Balanced waterbath
tubules
apart at
Tubules
were
with
fine
33#{176}Cto
Salt at
washed tweezers,
release
any
1984; Sylvester and Griswold, 1984). We have developed a system to study the binding and uptake of transferrin by intact, isolated rat seminiferous tubules wherein cell associations within
transferrin bound to the receptors 1983). After cooling on ice the ferred to the incubation medium. about 10-5 0 cm in length.
(Ciechanover tubules were The tubules
the tubules have not been disturbed testis barrier is intact. If we could use a heterologous
Tubular cubation
after 4 h of inblue exclusion test.
iron
donor,
secretion
we would route
be able
of transferrin
antibodies against (rat) transferrin.
uptake isolated
the
bloodas the
uptake
using
and the transferrin
and
specific
AND
rat
autologous is reported
transferrin
to
transferrin
was
purchased
from
tubules
I-FeTf
binding excess method Mendel albumin up by Wallace, incubation,
METHODS
Materials Human
The 125
integrity was at 33#{176}C with the or
33#{176}C(the ular cells,
donor for nonhuman cells et al., 1979; Perez-Infante compared the binding and
of human transferrin with rat seminiferous tubules. MATERIALS
the
transferrin
to study separately,
the heterologous Since human
to be an efficient iron (Messmer, 1973; Verhoef and Mather, 1982), we
and
Sigma
ice-cold amount counter.
125
checked Trypan
were
incubated
I-apoTf
for
2 h at 0#{176}C, or for
et
for al.,
best temperature Rommerts
was determined of unlabeled of Hamilton
with
rat
or
et al., transwere
human 4 h at
the culture of testic1980). Nonspecific
by incubation with a 20-fold protein, or according to the et al. (1984) and Mendel and
(1985).
Furthermore, the binding of 125 was studied, a molecule which is not taken seminiferous tubules in vivo (Setchell and 1972, the
Christensen tubules were
HBSS and of bound
et al., 1985). washed three times
lysed in 1 N NaOH, I was measured in
125
After with
and the a gamma
TRANSFERRIN
The
amount
of
to Lowry et protein content Values The
were results
(1949)
for
protein
was
al. (1951) of tubules expressed were
the
BINDING
determined
according
and compared of different known
per plotted
10 cm of according
determination
of
BY
with the lengths.
tubule length. to Scatchard
the
only
experiments
characteristic
examples
dissociation
of the
described
described
resulted in associations histologically; Figure the
method
blue) between microscopy
of spermatozoa
which
from the
isolation
and
prevented
entering Sertoli cells (not shown).
formed
at the
substances
the
tubule. were
1229
We studied the binding transferrins to such tubules concentration
in the
excess
of
unlabeled
or, according and Mendel plot above
of
different 125 I-labeled as a function of the
medium.
The nonspecific binding Fig. 2; 2a is the total method of Klausner
by
incubation
intact seminiferous tubules, where cell had not been disturbed (as checked results not shown). As can be seen in
1, a plug tubules,
for
TUBULES
was determined binding plot): et al. (1983b),
transferrin
to Hamilton (1985), the 4 izg/ml was
was
as follows according to a 20-fold
added
et al. (1984) slope of the extrapolated
(Fig.
2b),
and Mendel total binding back through
the origin (Fig. 2c). These methods gave comparable results. In addition, we studied the binding of 125 I.. albumin, which shows no specific binding or uptake
are shown. RESULTS
The
SEMINIFEROUS
(see the
constant (Kd) and the number of binding sites per 10 cm of tubule length (R0). The Student’s t-test was used for statistical analyses of the results. In the figures,
RAT
still
(e.g., Tight
visible
end
seminiferous
Christensen
tubules et al.,
(Setchell
1985;
Fig.
and
Wallace,
1972;
2d).
of
Trypan junctions
by electron 5
0
4
a 3 E U 0
C 2
2
4
6
8 nglml
FIG. 1. After 4 h of incubation at 33#{176}C,seminiferous tubules were transferred to a Trypan blue solution (1% in PBS). Trypan blue did not enter the tubules. At the open end of the tubule, a plug of spermatozoa formed, preventing substances from entering the tubules from this side.
10
12
14
16
F
FIG. 2. Comparison of different methods to determine the nonspecific binding: (a) O-O: total binding of ‘“I-human FeTf for 2 h at 0#{176}C as a function of the concentration in the medium; (b) t--t,: binding of 135 I-human FeTf for 2 h at 0#{176}Cwith a 20-fold excess of unlabeled human FeTf; (c) #{163}-#{149}#{149} -A: slope of the total binding curve extrapolated through the origin; and (d) #{149}-------S: binding of Ialbumin for 2 h at 0#{176}C.
1230
WAUBEN-PENRIS
ET
AL.
determined in Table
a
of
A
according 1. Rat FeTf
binding
length),
sites but
about
to Scatchard (1949), are shown and apoTf used the same number
(about
the
2 times
1010
Kd for
apoTf
higher
than
Mol/l) (p