J. Cell Sci. 42, 169-182 (1980)
Printed in Great Britain © Company of Biologists Limited igSo
ROLE OF CELL SURFACE RECEPTOR
MOBILITY IN CONCANAVALIN A-INDUCED
AGGLUTINATION OF NOVIKOFF HEPATOMA
AND NORMAL RAT LIVER CELLS
PAOLA MASTROMARINO, GIOVANNI NERI,* ANGELO SERRA
AND EARL F. WALBORG, jRf
Department of Human Genetics, Catholic University School of Medicine,
00168 Rome, Italy, and fThe University of Texas System Cancer Center,
Science Park-Research Division, Smithville, Texas 78957, U.S.A.
SUMMARY
The relationship between Con A-receptor mobility and Con A-induced agglutination of
Novikoff hepatoma and normal rat liver cells was investigated. Novikoff cells, incubated with
fluorescein-labelled Con A at 3 °C displayed uniform, ring-like surface fluorescence. Increasing
the temperature of the cells to 37 °C caused capping of Con A receptors in approximately 65 %
of the cells, a phenomenon that could be prevented by prefixing the cells with glutaraldehyde.
In spite of these variations in Con A-receptor distribution, Con A-induced agglutination was
remarkably constant over a temperature range from 3 to 37 °C. In contrast to NovikofF cells,
normal hepatocytes displayed a uniform, ringlike surface fluorescence at both 3 and 37 °C. No
capping was observed. However, hepatocytes, similar to Novikoff cells, were agglutinable by
low concentrations of Con A. These findings indicate that, in this model system, Con A-induced
cytoagglutination is not dependent upon long-range lateral mobility of Con A receptors. The
qualitative differences in the lateral mobility of cell-surface Con A leceptors of normal and
malignant rat liver cells may represent a marker for neoplastic transformation during hepatocarcinogenesis, adaptation to growth in ascitic form, or progression of a tumour to a more
malignant state.
INTRODUCTION
Since the first report by Aub, Sanford & Cote (1965) and subsequently by others
(Burger & Goldberg, 1967; Inbar & Sachs, 1969; Sela, Lis, Sharon & Sachs, 1970;
Nicolson & Blaustein, 1972) that malignantly transformed cells are more readily
agglutinated by plant lectins than their normal counterparts, a large effort has been
directed toward elucidation of the factors responsible for preferential lectin-induced
cytoagglutination of malignant cells (reviewed by Nicolson, 1974). In a very simplified
way, lectins can be viewed as acting like molecular bridges extending between
neighbouring cells and causing agglutination by a mechanism analogous to that
responsible for antibody-induced cell agglutination.
To determine whether alterations of cell-surface lectin receptors are responsible for
the increased agglutinability of tumour cells, investigations have focused mainly on
* To whom correspondence and reprint requests should be addressed at: Istituto di
Genetica Umana, Universita Cattolica, Via Pineta Sacchetti, 644-00168 Rome, Italy.
12
CEL42
170
P. Mastromarino, G. Neri, A. Sena and E. F. Walborg, Jr
cell-surface saccharide-containing components, particularly glycoproteins. Several
differences have been reported between normal and malignant cells with respect to
the number, structure, topography and dynamics of cell-surface lectin receptors
(reviewed by Smith & Walborg, 1977). Several hypotheses have been advanced to
explain the increased lectin-induced agglutination of tumour cells (Rapin & Burger,
1974; Smith & Walborg, 1977). To date, none of these hypotheses has proved of
general applicability, possibly because different mechanisms are operating in different
cell types. Moreover, the concept that increased agglutinability is a distinctive
property of cancer cells is no longer tenable. A number of studies on various mouse
tumours failed to show positive correlation between malignancy and lectin-induced
agglutinability (Gantt, Martin & Evans, 1969; Friberg, 1972; Dent & Hillcoat, 1972).
More recently Starling, Capetillo, Neri & Walborg (1977) showed that Novikoff
hepatoma cells and normal rat hepatocytes are both agglutinable by low concentrations of concanavalin A (Con A) and wheat germ agglutinin. In this same model
system, it was found that glutaraldehyde-fixed Novikoff cells were still agglutinable
by Con A, suggesting that Con A-induced agglutination of these cells is independent
of cell-surface receptor mobility (Walborg et al. 1975). Moreover, microfilamentactive drugs, such as cytochalasins b and d, proved capable of inhibiting Con Ainduced agglutination of Novikoff cells, but did not have any apparent effect on the
topography of Con A receptors (Glenney, Hixson & Walborg, 1979). The present
study was undertaken to clarify the relationship between Con A-induced cytoagglutination and the mobility of Con A receptors on Novikoff hepatoma and normal
rat liver cells.
MATERIALS AND METHODS
Cells
Novikoff hepatoma cells (Novikoff, 1957) were maintained in 6- to 10-week-old female
Sprague-Dawley rats (Charles River Italia, Calco, Italy) by weekly intraperitoneal transplantation. Normal hepatocytes were obtained as a suspension of cells (largely single cells)
from the liver of 6- to 10-week-old female Sprague-Dawley rats by the collagenase perfusion
method of Starling et al. (1977). Papain digestion and control incubation of Novikoff hepatoma
cells were performed as previously described (Neri, Smith, Gilliam & Walborg, 1974). Cell
viability was assessed on the basis of vital dye exclusion test, using nigrosine (Kaltenbach,
Kaltenbach & Lyons, 1958).
Labelling of Con A with fluorescein
Con A (Grade III Sigma Chemical Co., St Louis, Missouri) was conjugated with fluorescein
isothiocyanate component A (Serva Feinbiochimica, Heidelberg, West Germany) by direct
mixing at pH 90, as described by Mallucci (1976). The conjugate was purified by affinity
chromatography on a column of Sephadex G-50 (Pharmacia Fine Chemicals, Uppsala,
Sweden). Material that did not bind to the column or that could be removed by elution with
001 M glucose was discarded. The active fraction, eluted from the column with o-i M glucose,
was concentrated by ultrafiltration on Amicon PM 10 membrane (Amicon B.V., Costerhout,
Holland) to a volume of approximately 3-0 ml, and dialysed exhaustively against standard
salt solution, pH 7^4 (Mallucci, 1976) to remove glucose. The ratio of the optical densities at
495 and 280 nm, a measure of the degree of conjugation, was 0-5. The concentration of Con A
in the conjugate (53 mg/ml) was calculated from the extinction coefficient of the lectin
Con A receptor mobility and cytoagglutination
171
(E ascii'm = '3)> corrected for the absorption of fluorescein at 280 nm. A virtually identical
estimate of the concentration of Con A was obtained by an independent method, i.e. by
measuiing the haemagglutinating activity of fluorescein-labelled Con A (Fl-Con A) using the
haemagglutination assay of Smith, Neri & Walborg (1973). This assay also showed that
Fl-Con A had the same specific activity as freshly prepared, unlabelled Con A.
Assay of Con A receptor mobility
Untreated, control-incubated and papain-treated Novikoff cells or untreated normal
hepatocytes were washed three times in Ca3+- and Mg2+-free phosphate-buffered saline
(CMF-PBS) prepared according to Dulbecco & Vogt (1954), resuspended in the same buffer
at a concentration of 5 x io6 cells/ml and submitted to the following procedure. To a 4-ml
aliquot of cell suspension a specified amount of Fl-Con A was added, and the mixture allowed
to incubate for 30 min (unless otherwise specified) at either 3 °C, over crushed ice, at 23 °C,
in a temperature-regulated waterbath, or at 37 °C in a metabolic water incubator. Cell
suspensions were then chilled to 3 °C and washed 3 times with cold CMF-PBS in a refrigerated
centrifuge. The cells were resuspended in 4 ml of buffer and fixed for 30 min at 3 °C by
addition of glutaraldehyde to a final concentration of 2 %. The cells were subsequently washed
3 times in CMF-PBS, resuspended in 0-5 ml of the same buffer and observed under a coverslip
with a Leitz Orthoplan ultraviolet photomicroscope equipped with epi-illumination and
specific filters for fluorescein. In a few experiments the cells were fixed with glutaraldehyde
prior to incubation with Fl-Con A. The specificity of binding of Fl-Con A to the cell surface
was assessed by incubating the cells with Fl-Con A in presence of 0-5 M methyl-a-Dmannopyranoside (a-MM), a specific inhibitor of Con A (Poretz & Goldstein, 1970). Alternatively, cells incubated with Fl-Con A were washed 3 times in CMF-PBS and post-incubated
twice for 15 min at 37 °C in CMF-PBS containing of 02 M a-MM. Visual scoring of Fl-Con
A-labelled cells allowed their assignment to 1 of 3 classes of cells with different patterns of
fluorescence: ringlike, caplike and patchlike. The proportions of cells belonging to the 3 classes
were then estimated for the various experimental conditions, and the trend of these proportions
was analysed.
Cytoagglutination assays
Untreated, control-incubated or papain-treated Novikoff cells were washed 3 times in CMFPBS and assayed for Con A-induced agglutination following the procedure of Neri et al. (1974).
Con A, purchased from Pharmacia Fine Chemicals, was dissolved in CMF-PBS. Protein
concentration was determined spectrophotometrically using the extinction coefficient,
E 28<tam = X3- The cytoagglutination assays were performed at 3, 23 and 37 °C, with different
concentrations of Con A. For the assay at 3 °C, the cytoagglutination plates were set on a thin
metal sheet lying over a pan filled with crushed ice. After pipetting the cells and the lectin into
the wells, and mixing with a toothpick, the plates were transferred to the cold room, and
removed 30 min later for microscopic scoring. For the assay at 23 °C, all operations were
performed at room temperature. For the assay at 37 °C, pipetting of the lectin and cells and
mixing were performed at room temperature. The plates were then immediately transferred
to an incubator at 37 °C, covered with Petri dishes to minimize evaporation, and removed
30 min later for scoring. All agglutination assays were repeated on different days using fresh
reagents. The degree of agglutination was scored visually on a serological scale from o to 4
(Wray & Walborg, 1971). Then, the least square regression lines of agglutination on the log
of the Con A concentration at the 3 temperatures were fitted.
RESULTS
Con A receptor mobility of Novikoff cells
Incubation of Novikoff cells with Fl-Con A resulted in labelling of the cell surface
in a ringlike or in a caplike pattern. Caps could take the form of either a protruding
fluorescent mass at the uropod of the cell, or a condensation of fluorescence at one
172
P. Mastromarino, G. Neri, A. Serra and E. F. Walborg, Jr
Con A receptor mobility and cytoagglutination
173
pole of the cell. Cell-surface labelling was specific, and could be completely inhibited
by the presence of 0-5 M a-MM. Discrete patches of fluorescence were also observed
in some of the cells scored. The location of these patches at the surface of the cells
seems unlikely since they could not be removed by postincubation of the cells with
a-MM. Examples of these fluorescence patterns are illustrated in Fig. 1 (panels
A-E). The cells shown in the plate were incubated with Fl-Con A (66/tg/ml) for
30 min at 37 °C (except for panel A, showing a cell incubated at 3 °C). These experimental conditions yielded maximal capping as shown in Figs. 2 and 3. Fig. 2, where
the percentage of cells with cap is plotted against the concentration of Con A, shows
that at 66 /<g of Con A/ml the proportion of cells with cap was maximal. This concentration of Con A is sufficient for maximal cell agglutination (Neri et al. 1974). In
receptor-mobility experiments, however, cytoagglutination was largely prevented by
using conditions, such as low cell concentration and repeated pipetting of the cell
suspension, that would minimize cell-cell contacts. The incubation time (30 min)
was chosen to render receptor mobility data directly comparable to cytoagglutination
data, previously standardized on a 30-min incubation (Neri et al. 1974), and was
optimal in terms of allowing maximal capping. This is shown in Fig. 3, where the
percentage of cells with cap is plotted against time.
50
75
100
125
150
[Con A ] , /jg/ml
Fig. 2. Cap formation in Novikoff cells incubated with various concentrations of
Fl-Con A for 30 min at 37 °C.
Fig. 1. Patterns of fluorescence in Novikoff cells (A-E) and normal hepatocytes (F)
treated with Fl-Con A (66 fig Con A/ml) for 30 min at 37 CC (except for A, showing
a cell incubated with Fl-Con A at 3 °C). x 540. A, ringlike pattern; B, cap; c, uropodal
cap; D, patchlike pattern; E, absence of cell-surface fluorescence in Novikoff cells
treated with Fl-Con A in presence of 0-5 M a-MM; F, ringlikefluorescencein normal
hepatocyte.
174
P- Mastromarino, G. Neri, A. Serra and E. F. Walborg, Jr
The proportions of Novikoff cells showing ring, cap or patch fluorescence at the
3 temperatures tested, and at a Con A concentration of 66/tg/ml, are reported in
Table i. In untreated cells, incubation with Fl-Con A at 3 °C resulted in the
appearance of ringlike fluorescence in 95 % of the cells, and of caps (all non-uropodal)
40
60
Incubation time, min
Fig. 3. Cap formation in Novikoff cells incubated with Fl-Con A (66 fig Con A/ml)
for different times at 37 °C.
Table 1. Pattern offluorescence'1of Novikoff cells at different temperatures
Temperature, °C
A
3
23
A
Treatment
of cells
Untreated"
Incubatedd
Papain treated"
N6
216
223
211
37
A
R,
%
c,
%
95
87
5
3
70
19
P, N"
%
R,
%
c,
%
P,
R,
%
c,
%
P,
/n
227
84
90
79
16
442
6 496
10 4Si
31
27
36
65
68
31
4
5
33
0
10
11
677
825
4
11
O
N"
0/
/o
" The pattern of fluorescence was designated: R = ringlike; C = caplike; P = patchlike.
6
Total no. of cells scored.
c
Cells washed 3 times in PBS.
d
Cells incubated for 40 min in Buffer II (Wray & Walborg, 1971) at 37 °C.
" Cells incubated as in d above, but in presence of 2 units of papain (Worthington Biochemical
Co., Freehold, N J . ) per ml of cell suspension containing io 7 cells/ml.
in 5%. Increase in temperature was accompanied by a significant shift in the pattern
of surface fluorescence from ringlike to caplike. The increase in the percentage of
capped cells from 3 to 37 °C was about 13-fold. The trend analysis of proportions of
capped cells showed that the observed increase with the temperature is not linear.
Con A receptor mobility and cytoagglutination
175
The appropriate statistics (Armitage, 1971; Snedecor & Cochran, 1971) indicated
that the deviation of proportions from their linear regression on the temperature is
highly significant (Xi = 23-485; P < o-ooi), suggesting that a sudden change
probably occurs at 37 CC. Patchlike fluorescence was absent at 3 or 23 °C, and present
in only 6% of the cells incubated at 37 °C. Control-incubated cells behaved in an
apparently identical way. Here also, the deviation from linearity was highly significant
Cd = J64"47o; P < o-ooi). Treatment of Novikoff cells with papain resulted in the
appearance of a relevant proportion of cells with caplike fluorescence at 3 °C. The
percentage of capped cells increased further upon raising the temperature to 37 °C,
at which, however, their proportion was only 31%, significantly lower than that
observed in the untreated or control-incubated cells. This effect is clearly correlated
with a significant increase in the number of cells displaying patchlike fluorescence.
Nevertheless, the deviation from linearity, suggesting a sudden change at 37 °C, was
evident also in this experimental condition (xt = 44' 1 1 2 ! P < o-ooi). Fixation of
Novikoff cells with glutaraldehyde prior to incubation with Fl-Con A under any of
the experimental conditions employed, resulted in a pattern of surface fluorescence
comparable to that observed at 3 °C under those same conditions.
Con A-receptor mobility of normal hepatocytes
Isolated normal rat hepatocytes were incubated with Fl-Con A under experimental
conditions identical to those described for Novikoff cells. Only untreated cells, i.e.
cells that had not undergone papain treatment or control incubation, were tested.
Surface fluorescence had a ringlike form in 100% of the viable cells at all 3 temperatures tested, and at Con A concentrations ranging from 1-3 to 66/tg/ml. The latter
concentration was routinely used, because it gave more distinct and visible rings. A
normal hepatocyte is illustrated in Fig. I F .
Effect of temperature upon cytoagglutination of Novikoff cells
The fitted least-square lines of regression of Con A-induced agglutination of
Novikoff cells upon Con A concentration at 3, 23 and 37 °C are reported in Fig. 4.
It clearly appears, on inspection, that agglutination is dependent on the concentration
of Con A. The intercept of each agglutination line with the abscissa represents the
concentration of Con A required for threshold agglutination at that particular
temperature. The point on the abscissa corresponding to the score value of 2 on the
ordinate represents the concentration of Con A necessary for half-maximal agglutination. Threshold and half-maximal values are reported in Table 2. The untreated
cells show at 37 °C a slight increase in agglutinability, since a smaller concentration
of Con A is required for threshold and half-maximal agglutination. Although a
constant enhancement of agglutinability at 37 °C is also suggested by the parallelism
of the regression lines (Fig. 4A) the approximate standard error of the estimated line
(sy_x = + 0-485) indicates, however, that such increase cannot be considered significant.
The behaviour of the control-incubated cells was virtually superimposable on that of
the untreated cells. Treatment of the cells with papain caused an increase in agglutinability by Con A, an effect that had been previously observed (Neri et al. 1974). At
176
P. Mastromarino, G. Neri, A. Serra and E. F. Walborg, Jr
the same mean concentration of Con A (log x = 1-32) the mean agglutinability at
37 °C was 3-13 + 0-27 for papain-treated cells against 2-48 + 0-12 for incubated cells
or 2-27±o-io for untreated cells. A test for the difference of means shows that this
increase is significant both with respect to untreated cells (t = 2-938; P < o-ooi)
and to incubated cells (t = 2-667; P < o-ooi).
37° 3° 23°
5
25
100
[Con A],
Fig. 4A For legend see page 178.
DISCUSSION
Interest in lectin-induced cell agglutination was greatly stimulated by the observation that neoplastic cells are usually agglutinated by lower concentrations of lectins
than their normal counterpart. The molecular mechanisms responsible for the
differential lectin-induced cytoagglutination of normal and malignant cells has been
the subject of numerous investigations (Nicolson, 1974; Smith & Walborg, 1977).
Much of this research focused on the role of lectin receptor mobility as a determinant
of lectin-induced cytoagglutination. From work of Rosenblith, Ukena, Berlin &
Karnowski (1973), of Nicolson (1973) and of Guerin et al. (1974) it might be con-
Con A receptor mobility and cytoagglutination
177
eluded that clustering of lectin receptors in discrete areas of the cell surface is a
prerequisite for the increased agglutination of transformed cells. The evidence,
however, is only circumstantial, since, as pointed out by Smith & Walborg in their
comprehensive review (1977), these authors did not investigate the agglutinabihty of
cells carrying clustered sites (e.g. transformed cells incubated with Con A at 37 °C)
37"
Z- 2
S1
/
I
5
25
100
[Con A], /jg/ml
Fig. 4B For legend see page 178.
as compared with the same cells carrying uniformly distributed sites (transformed
cells incubated with Con A at o °C). More direct evidence was provided by Inbar
et al. (1973), who showed that aldehyde fixation of mouse lymphoma cells inhibited
agglutination by Con A. Similarly, Noonan & Burger (1973) reported that Py3T3 or
SV3T3 cells, that were not agglutinable by Con A at o °C, became agglutinable
when the temperature was raised to 22 °C. On the other hand, Schnebli et al. (1977),
in a series of detailed studies utilizing human erythrocytes as well as cells from normal
and malignant tissues, came to the conclusion that cell agglutination by Con A was
not blocked at o °C, a temperature at which mobility of receptors in the plane of the
membrane was inhibited. Rutishauser & Sachs (1974), in a study utilizing normal
178
P. Mastromarino, G. Neri, A. Serra and E. F. Walborg, Jr
mouse lymphocytes and lymphoma cells attached to nylon fibres, provided evidence
that cell-cell binding induced by Con A required short-range lateral movements of
cell-surface lectin receptors, and that clustering of the receptors was not necessary and
seemed to hinder cell-cell binding.
The purpose of the present report was to clarify the relationship between the
I
25
[Con A], jug/ml
100
Fig. 4. Estimated regression lines of the degree of agglutination upon Con A concentration at temperatures of 3, 23 and 37 °C respectively, A, untreated cells; B,
control-incubated cells; C, papain-treated cells. Abscissa: Con A concentration on
a logarithmic scale. Ordinate: agglutination scores. The dotted lines represent the
approximate standard error of the estimated regression line at 37 °C.
topography and dynamics of Con A receptors at the cell surface and Con A-induced
cytoagglutination of normal and malignant rat liver cells. These studies utilized
Novikoff hepatoma cells and normal rat hepatocytes, cells that are agglutinable by
low concentrations of Con A (Neri et al. 1974; Starling et al. 1977). We took advantage
of the fact that lectin-induced receptor movement is a temperature-dependent
phenomenon and can be blocked at 0-4 °C, when the membrane lipid bilayer is
Con A receptor mobility and cytoagglutination
179
'frozen' (Reinert & Steim, 1970). Con A receptor movements were monitored at
various temperatures utilizing fluorescein-conjugated Con A, and were compared
with Con A-induced agglutination, scored under the same experimental conditions,
using a modification of a previously described method (Neri et al. 1974). We found
that temperature variations had profound effects on the distribution pattern of Con A
Table 2. Con A concentration (/<g/ml)fcr threshold and half-maximal agglutination
of Novikoff cells at different temperatures
Temperature, °C
23
Treatment of cells
Untreated"
Incubated"
Papain-treated"
Thresh." i/2Max
45
31
0-45
250
190
60
4
Thresh." 1/2M1K'
4-0
30
0-75
250
220
ic-6
37
*
Thresh." i/2Max 6
28
2-1
014
i6'3
125
36
" Threshold agglutination.
b
Half-maximal agglutination.
<=•*•• As in Table 1.
receptors on Novikoff cells. At 3 °C the distribution was uniform over the entire cell
surface as indicated by the ringlike shape of the membrane fluorescence in 95 % of
the cells examined. This uniform distribution probably represents the inherent
topographical pattern of the Con A receptors, since an identical pattern was observed
when the cells were fixed with glutaraldehyde, prior to incubation with Fl-Con A.
Upon shifting the temperature to 37 °C, the Con A receptors underwent a redistribution, as indicated by the appearance of caps in 65% of the cells scored. In a few
cells the fluorescence appeared clustered in discrete patches over the cell. However
appropriate controls in presence of a-MM, indicated that the fluorescence could not
be removed by post-incubating the cells with a-MM, suggesting that the fluorescent
patches were intracellular and probably represented pynocytosed material. The
situation at 23 °C was similar to that observed at 3 °C. This accounts for the nonlinearity of the increase of the proportion of capped cells with temperature, but seems
rather surprising, since the transition temperature of the membrane lipids is below
23 °C (Reinert & Steim, 1970). At the latter temperature the lipid bilayer should be
in a fluid state and should allow lateral diffusion of membrane macromolecules. If
this does not happen, the most likely explanation is that the process of cap formation
requires energy and is therefore partially inhibited at 23 °C. The previous observation
of Glenney et al. (1979) that at 22 °C ferritin-labelled Con A was uniformly distributed
over the surface of Novikoff cells, is in agreement with the present finding.
In spite of these variations in Con A-receptor distribution, Con A-induced cell
agglutination was remarkably stable over the temperature range from 3 to 37 °C.
This observation suggests that Con A-induced agglutination of Novikoff cells does
not depend upon diffusion and capping of the lectin receptors. It was previously
180
P. Mastromarino, G. Neri, A. Sena and E. F. Walborg, Jr
demonstrated that Novikoff cells become more agglutinable by Con A after papain
treatment (Neri et al. 1974). This finding was quantitatively confirmed in the present
report, and additional evidence was provided, showing that the papain effect was of
the same magnitude at each of the 3 temperatures tested. On the other hand,
temperature-dependent Con A-receptor diffusion could still be observed in the
papain-treated cells, indicating once more that capping of receptors and cytoagglutination varied independently. The only significant effect of papain treatment upon
Con A-receptor dynamics, especially apparent at 37 °C, was an enhanced internalization of Fl-Con A, as indicated by the increased percentage of cells with patchlike
fluorescence, that could not be removed by post-treatment with a-MM. A less
marked effect was the appearance of caps in a small percentage of cells incubated with
Fl-Con A at 3 °C.
Additional evidence that cytoagglutination is not dependent upon receptor
clustering was provided by a study of normal rat hepatocytes. These cells are also
agglutinable by low concentrations of Con A (Starling et al. 1977). Yet, when assayed
for receptor mobility using Fl-Con A, all of the viable cells scored invariably displayed
a ring of surface fluorescence with no evidence of receptor diffusion and redistribution
into caps or patches, even at 37 °C. The molecular basis for the observed difference
in Con A-receptor mobility between normal hepatocytes and hepatoma cells is
presently unclear. At any rate, it may be concluded that Con A-induced cytoagglutination and long-range Con A-receptor mobility vary independently in normal
hepatocytes and Novikoff hepatoma cells. Furthermore Con A-receptor mobility
may represent another marker of neoplastic transformation during hepatocarcinogenesis, adaptation to growth in the ascitic form, or progression of a tumour to a more
malignant state.
This work was supported in part by grant NCT 75 00699.04 from the Consiglio Nazionale
delle Ricerche of Italy.
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(Received 17 July 1979)