[CANCER RESEARCH 37, 1618-1623, June 1977]
Immunofluorescent Characterization of Rat Kidney Tumors
According to the Distribution of Actin as Revealed by
Specific Antiactin Antibody1
Gordon C. Hard2 and B. H. Toh
Baker Medical Research Institute (G. C. HI, and Department of Pathology and Immunology, Monash university Medical School, Commercial Road, Prahran,
Victoria 3181, Australia (B. H. T.j
SUMMARY
A series of 15 mesenchymal and 10 cortical epithelial
tumors induced in the rat kidney by dimethylnitrosamine
was investigated for immunofluorescent reactivity with a
human antiactin antibody. Cells of epithelial tumors showed
staini ng restricted to peripheral sites, corresponding to the
brush border region. All various neoplastic cell forms corn
prising renal mesenchyrnal tumor were characterized by
cytoplasmic staining in patterns that varied with cell type.
Epithelial profiles in the form of tubules and islands of
epitheliurn showed staining patterns, or absence of them,
consistent with their identity as sequestered segments of
preexisting nephrons. It is suggested that the difference in
actin distribution within the cytoplasm of cells of the two
types of renal neoplasm, mesenchymal and epithelial, might
reflect their difference in local invasive growth.
INTRODUCTION
Renal tumors may be induced in rats with a broad range
of chemicals including nitroso compounds such as DMN3
and rnethylnitrosourea (for review, see Ref. 3). Most corn
monly, the induced neoplasms are either cortical epithelial
tumors conforming to adenoma, adenocarcinoma, or carci
noma, or they are connective tissue mesenchymal tumors.
The former display the usual spectrum of histological pat
terns seen in humans, ranging from papillary to lobular and
solid, and take origin in the tubule elements, particularly
proximal tubules of the cortex (4, 8, 9). On the other hand,
the mesenchymai tumors have proved more difficult to in
terpret, and their characteristic cellular heterogeneity has
resulted in such diverse classifications as renal sarcoma,
hemangioendothelioma , and neph roblastoma or Wilrns' tu
rnor. Light and electron microscopic studies of these flea
plasms (4, 7) and their genesis (5, 6) indicate that they are
mesenchymal in nature, deriving from a mesenchymal cell
type resident in the interstitial space of the outer kidney
zones. Histologically, the tumors consist of an admixture of
fibroblast-like spindle cells, smooth muscle fibers, primitive
or embryonic mesenchyrne, and areas of neoplastic vascu
lar tissue. On occasion, straited muscle, cartilage, and os
teoid are present also (4, 7). Cqnfusion with true nephro
blastoma leading to error in nomenclature arises from 2
aspects (10). First, in proliferating between the tubules of
the parenchyrna, neoplastic rnesenchymal cells progres
sively incorporate preexisting epithelial elements into the
tumor tissue. Many of the engulfed tubules remain intact
but show such pathological alteration as dilation to form
cystic spaces, collapse with lumenal obliteration, and hy
perplastic proliferation of the lining cells. Where neoplastic
mesenchyme invades the hilus, tongues or islands of hyper
plastic transitional epitheliurn derived from the urothelial
lining of the pelvis become incorporated into the tumor
mass. A 2nd source for misinterpretation lies in the predi
lection for mesenchymal tumor cells to condense around
sequestered epithelial profiles in concentric layers, thus
resembling the disposition of cells in nephroblastorna (10).
in a previous study (16), we have demonstrated that cells
in renal rnesenchymal tumors induced by a single injection
of DMN showed strong cytoplasmic staining with a human
AAA in contrast
to the weak, nondescript
staining
of the
resident interstitial cells from which the tumors are believed
to be derived. This enhanced reactivity of tumor over nor
mal cells with AAA has also been observed with tumors
originating in skin (17), glial tissue (18), and liver (14).
In this study, we have examined the AAA staining patterns
that characterize the common renal tumors of the rat, corn
paring, in particular, the difference between cortical epithe
hal and mesenchymal tumors and describing the reactivity
of the heterogeneous cell forms which comprise the latter,
including their epithelial profiles.
MATERIALS AND METHODS
IThis
research
was
supported
bytheA.A.Thomas
Fellowship
oftheAnti
Characterization of Human AAA. The AAA serum ob
tamed from a patient with active chronic hepatitis was char
acterized by reactivity with the following tissues: smooth
muscle (11), skeletal muscle (12), liver parenchymal cells
University of Melbourne Medical Centre, Grattan Street, Parkville, Victoria
3052, Australia. To whom requests for reprints should be addressed.
(2), thymic medulla, renal glorneruli (19), brush border and
3Theabbreviations
used
are:DMN,
dimethylnitrosamine;
AAA,
antiactinperitubular fibrils of renal tubules (16), and central nervous
antibody.
Received December 30, 1976; accepted March 1, 1977.
system synaptic endings (15).
Cancer Council of Victoria and grants from the Anti-Cancer Council and the
National Health and Medical Research Council.
2 Arthur
1618
A.
Thomas
Fellow.
Present
address:
Department
of
Pathology,
CANCER RESEARCHVOL. 37
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Reactivity
of Rat Kidney Tumors with AAA
outlined by positively staining supporting stroma. In 1 solid
Immunohistology. Six-pm cryostat sections of tumor tis
carcinoma consisting of an intermixture of areas of clear
sue were stained with AAA by the standard “sandwich―
immunofluorescence test (13), using sera at a dilution of and eosinophilic cells, the latterdisplayed the characteristic
peripheral staining pattern while the clear cells were nega
1:8. The conjugate for immunofluorescent tracing of bound
tive. The larger tumors contained frequent foci of necrosis
immunoglobulin was a fluorescein isothiocyanate-labeled
which were always totally lacking in reactivity. Adenomas
goat anti-human y-globulin with a fluorescein:protein molar
were generally typified by fluorescence patterns similar to
ratio of 4.0 and a protein content of 0.8 g/100 ml. Before
use, the conjugate was absorbed with homogenates of rat the larger epithelial tumors but the staining could also be
weak or mainly negative (Fig. 8).
liver, kidney, and gastrointestinal tract, and smooth muscle
Mesenchymal Tumors. In contrast to the epithelial neo
of pig stomach, until there was no staining reaction on test
plasms, the complete range of mesenchyrnal tumor cell
sections of normal kidney and tumor tissue. After immuno
types was characterized by positive cytoplasmic staining
fluorescent staining, the tissue preparations were examined
with AAA serum. Spindle or fibroblast-like cells forming the
by dark ground UV fluorescence microscopy using a con
invading edge of the tumors (Figs. 9 and 10), swirling in
denser fitted with a colorless barrier filter and toric lens.
concentric layers around engulfed tubules (Figs. 11 and 12)
Specificity of the tests was established by failure to obtain
or forming fibrosarcoma-like sheets, showed brightly fila
staining with parallel control sections treated with normal
mentous cytoplasmic staining. Areas consisting of smooth
human serum or AAA serum neutralized with actin derived
muscle (Fig. 13) were thrown into strong relief from the
from smooth (16) or skeletal muscle (1, 15).
Induction of Renal Tumors. A series of 15 mesenchymal surrounding mesenchyrne by intense staining of a compact,
sheet-like nature. Rhabdomyoblasts and mature striated
tumors and 10 cortical epithelial tumors were characterized
muscle were typified by an intense fibrillar or swirling pat
by their immunofluorescent reactivity with AAA. The neo
tern of staining (Fig. 14). Stellate cells forming areas that
plasms were induced in rats of Porton albino Wistar stock
by the i.p. administration of a single dose of 60 mg/kg. The resembled embryonic mesenchyme (Figs. 15 and 16) re
rats had been treated for 3 to 5 days previously with a diet of acted positively with a filamentous or stippled staining pat
sugar and water, a regimen which leads to a 100% renal tern. In islands of cartilage (Figs. 17 and 18), the chrondro
cytes showed a coarsely granular to diffuse cytoplasmic
tumor incidence (4). Neoplasms were excised from anesthe
tizedratsat intervals
rangingfrom 6 to 12 months after staining, with the matrix remaining negative. Likewise, neo
plastic bone-forming cells stained positively but the osteoid
carcinogen treatment. Tumor specimens were snap-frozen
in an isopentane:Iiquid nitrogen slurry at —170°
for tests was negative. Acellular myxoid zones and tufts and sheets
of collagen did not react with the AAA serum.
with AM serum. Companion histological samples were pre
At the invading edges of rnesenchymal tumors, where
pared by staining cryostat and paraffin-embedded sections
neoplastic cells infiltrated between preexisting nephrons,
with hematoxylin and eosin.
the recently surrounded tubule profiles of the outer kidney
zones usually retained bright staining restricted to the lu
menal surfaces, indicative of brush border reaction (Fig. 9),
RESULTS
whereas those of the inner, medullary zones were lacking in
reactivity (Fig. 10). With progressive engulfment, cortical
The general morphology of DMN-induced renal mesen
tubules frequently became partially or entirely negative
chyrnal and cortical epithelial tumors has been described
and comprehensively depicted in earlier publications (4, 7, (Figs. 12 and 13), including some of those in which hyper
plasia occurred. Where tumor cells invaded the hilus, long
8). To avoid unnecessary duplication of illustrative material,
tongues of transitional epithelium from the urothelial lining
the reader is referred for details of histology and ultrastruc
were engulfed by the proliferating mesenchyrne. These of
ture to those previous reports in this journal.
ten appeared as isolated islands of epithelium surrounded
Cortical Epithelial Tumors. In each neoplasm examined,
by condensations of neoplastic spindle cells or primitive
the cytoplasm of constituent tumor cells was consistently
mesenchyme (Fig. 15). Such elements were characteristi
negative for AAA staining reactivity. Characteristically, how
cally negative, contrasting with the positive staining of the
ever, there was a linear staining in epithelial cells conform
surrounding malignant mesenchyme (Fig. 16).
ing to the peripheral location and incidence of brush bor
der. Additionally, the supporting stroma, consisting of fi
brocytes and cells of blood vessel walls, stained positively.
DISCUSSION
Thus, in papillary adenocarcinoma (Figs. 1 and 2), col
urnns of epithelial cells supported by central spines of posi
Comparative studies on the immunofluorescence reactiv
tively staining stroma showed bright linear staining re
ity of renal tumors with AAA show distinctive differences in
stricted to the outer edge of their free surfaces. In tubular
the staining patterns between cortical epithelial tumors and
adenocarcinoma (Figs. 3 and 4), tumor cells displayed sirni
lar staining along the internal apical or lurnenal borders. In mesenchymal tumors of the rat kidney. The cytoplasm of
epithelial tumor cells is essentially negative, the reaction
the lobular (Figs. 5 and 6) and solid (Fig. 7) forms of adeno
carcinoma-carcinoma,
a substantial proportion of cells zone being restricted to peripheral borders or free edges,
sites ultrastructurally associated with brush border forma
showed a thin line of fluorescence around the entire periph
ery of individual cells or encircling small groups of 2 or tion (8). The localization of reactivity to sites indicative of
brush border in almost all of the epithelial tumors examined
more cells. Lobules and larger solid areas were themselves
JUNE 1977
1619
Downloaded from cancerres.aacrjournals.org on July 28, 2017. © 1977 American Association for Cancer Research.
G.
C@
Hard
and
B.
H.
Toh
is in agreement with the proposed derivation of many of
these neoplasrns from the proximal segment of the nephron
(8, 9).
In contrast, all of the cell forms that comprise renal mes
enchyrnal tumor, excluding epithelial profiles, are char
acterized by reactivity throughout their cytoplasm, in pat
terns that vary with the cell type. This is a predictable result
in keeping with the belief that the neoplasrns are essentially
of connective tissue nature and derived from a resident in
tertubular, rnesenchymal cell (4-7). The variations in stain
ing pattern that occur within the heterogeneous range of
cell forms enable various components of the tumors, namely
smooth muscle, to be recognized easily. As has been
pointed out in a previous study (16), the staining reactivity
of mesenchymal tumor cells is enhanced beyond the weak
reaction typical of the original, resident fibrocyte-like cells
of normal interstitiurn. The staining characteristics of epi
thelial profiles incorporated within the mesenchyrnal tumor
tissue are consistent with their origin from preexisting
nephrons which have become sequestered by the infiltrat
ing tumor cells. Staining restricted to the brush border of
proximal tubules often becomes lost with progressive en
gulfrnent and pathological alteration.
The specificity of the AAA serum used in this study per
mits the conclusion that epithelial cells of rat kidney contain
actin only at the cell periphery, presumably in microvillous
structures, whereas all neoplastic cells in mesenchyrnal
tumors possess actin distributed throughout the entire cy
toplasm. This morphological difference in actin content
may reflect a basic difference in the growth behavior of the
2 neoplasrns. Mesenchymal tumor cells are locally very
invasive, infiltrating and proliferating between the nephrons
without a capsular reaction. On the other hand, growth of
cortical epithelial tumors (with the exception of the infre
quent anaplastic type not represented in this study) is
largely a passive process occurring by slow outward expan
sion of the cell aggregate and stimulating a distinct capsule
like reaction. Thus, local invasiveness of mesenchymal tu
mor cells and the sessile nature of the epithelial cells may
be functions of the cytoplasmic distribution of actin.
The observed differences noted in cytoplasmic distribu
tion of actin may provide an additional basis for distinction
between kidney tumor and cell types. Although there is
usually little problem in distinguishing between mesenchy
mal and cortical epithelial tumors by conventional histologi
cal methods, some additional aid is necessary in those
cases of mixed tumors where the epithelial cell components
lose their cohesive growth properties. Furthermore, in cell
culture, differentiation on morphological grounds between
mesenchyrne and epitheliurn can be difficult, and it is antici
pated that the technique described here may be of value in
establishing cell identity under such conditions. The induc
ing carcinogen used in this study is not associated with the
production of nephroblastornas, the neoplasm with which
renal mesenchyrnal tumor is most likely to be confused.
Fresh tissue specimens of rat nephroblastoma were not
available for comparison due to the infrequency of the
1620
neoplasm's occurrence (reviewed in Ref. 10). Conse
quently, differential staining reactivity with AAA of the rnes
enchyrnal and epithelial components of a range of human
Wilms' tumors is presently under investigation.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the technical assistance of Vivian
Randell and John Lee.
REFERENCES
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Troponin: Evidence for Multiple Forms of Troponin-T. Biochim. Biophys.
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2. Farrow, L. J., Holborow, E. J., and Brighton, W. D. Reaction of Human
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3. Hard, G. C. Experimental Tumours. In: D. I. Williams and G. C. Chisholm
(eds.), Scientific Foundations in Urology, Vol. 2, pp. 255-264. London:
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4. Hard, G. C., and Butler, W. H. Cellular Analysis of Renal Neoplasia:
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Johnson, G. D., Holborow, E. J., and Glynn, L. E. Antibody to Smooth
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12. Lidman, K., Biberfield, G., Fagraeus, A., Norberg, R., Torstensson, R.,
Utter, G., Carlsson, L., Luca, J., and Lindberg, U. Anti-Actin Specificity
of Human Smooth Muscle Antibodies in Chronic-Active Hepatitis. Clin.
Exptl. lmmunol., 24: 266—272,
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13. Nairn, A. C. Fluorescent Protein Tracing, pp. 373-377. Edinburgh:
Churchill-Livingstone, 1976.
14. Toh, B. H., Cauchi, M. N., Muller, H. K., and Hard, G. C. The Relevance
of Smooth Muscle-Associated Antigens in Cancer. In: H. E. Nieburgs
(ed), Detection and Prevention of Cancer, in press.
15. Toh, B. H., Gallichlo, H. A., Jeffrey, P. L., Livett, B. G., Muller, H. K.,
Cauchi, M. N., and Clarke, F. M. Anti-Actin Stains Synapses. Nature, 264:
648-650, 1976.
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Associated Contractile Protein in Renal Mesenchymal Tumour Cells and
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CANCER RESEARCHVOL. 37
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Fig. 1. Adenocarcinoma with papillary form. H & E, x 150.
Fig . 2. Papillary adenocarcinoma. Staining by AAA is restricted to the free borders of the cords of epithelial cells. The central columns of supporting stroma
are also positive. Indirect immunofluorescence, x 320.
Fig. 3. Adenocarcinoma with tubular differentiation. H & E, x 290.
Fig. 4. Tubular adenocarcinoma. Staining by AAA is restricted to the stroma at bottom left and the internal or Iumenal borders of epithelial cells. Indirect
immunofluorescence, x 320.
Fig. 5. Adenocarcinoma with lobular pattern. H & E, x 200.
Fig. 6. Lobular adenocarcinoma. Interlobular stroma shows bright immunofluorescence with AAA while small groups of epithelial cells within lobules are
outlined by thin, peripheral staining. Indirect immunofluorescence, x 320.
JUNE 1977
Downloaded from cancerres.aacrjournals.org on July 28, 2017. © 1977 American Association for Cancer Research.
1621
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Fig . 7. Adenocarcinoma of solid pattern . Individual epithelial cells or small groups of cells are clearly outlined by peripheral staining with AM, but the main
area of cytoplasm is negative. Indirect immunofluorescence, x 500.
Fig. 8. Small adenoma shows weak peripheral staining by AAA in a few epithelial cells but is largely negative. Indirect immunofluorescence, x 320.
Fig. 9. Mesenchymal tumor. Spindle cells swirling between proximal tubules at the invading edge show brightly filamentous staining of cytoplasm by AAA.
The engulfed tubules show staining of the apical brush border region. Indirect lmmunofluorescence, x 320.
Fig. 10. Mesenchymal tumor. Invading edge of tumor in the inner kidney zones shows spindle cells with bright cytoplasmic staining by AAA, infiltrating
between negative medullary tubules. Indirect immunofluorescence, x 160.
Fig. 11. Mesenchymal tumor. Characteristically, spindle cells become stratified in concentric layers around some sequestered tubules, an arrangement
that mimics rat nephroblastoma. H & E, x 625.
Fig. 12. Mesenchymal tumor. Concentric layers of spindle cells stain brightly with AAA contrasting with the surrounded tubule which is negative but for
partial staining of the brush border zone. Indirect immunofluorescence, x 260.
1622
CANCER RESEARCH VOL. 37
Downloaded from cancerres.aacrjournals.org on July 28, 2017. © 1977 American Association for Cancer Research.
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Fig. 13. Mesenchymal tumor. Smooth muscle surrounding engulfed tubules shows compact, sheet-like staining of the cytoplasm by AAA. Some residual
tubules show weak staining of the brush border zone; others are negative. The pooriy cellular myxoid areas beyond the smooth muscle are also negative.
Indirect immunofluorescence, x 320.
Fig. 14. Mesenchymal tumor. Rhabdomyoblasts show bright fibnillary staining by AAA. Indirect immunofluorescence, x 320.
Fig. 15. Mesenchymal tumor. Tumor cells in the pattern of embryonic mesenchyme condense around islands of engulfed urothelial cells where invasion
of the pelvis has occurred. H x E, x 200.
Fig. 16. Mesenchymal tumor. Tumor cells In the pattern of embryonic mesenchyme show bright cytoplasmic staining by AAA which outlines the negative
islands of transitional epithelium derived from the urothelial lining of the pelvis. Indirect immunofluorescence, x 200.
Fig. 17. Mesenchymal tumor. Islands of neoplastic cartilage within a spindle cell area. H x E, x 200.
Fig. 18. Mesenchymal tumor. The matrix of the cartilage is negative, while the chondrocytes show a coarsely granular or diffuse cytoplasmic staining by
AAA. Indirect
immunofluorescence,
JUNE 1977
x 200.
1623
Downloaded from cancerres.aacrjournals.org on July 28, 2017. © 1977 American Association for Cancer Research.
Immunofluorescent Characterization of Rat Kidney Tumors
According to the Distribution of Actin as Revealed by Specific
Antiactin Antibody
Gordon C. Hard and B. H. Toh
Cancer Res 1977;37:1618-1623.
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