Expression of platelet-derived growth factor (PDGF)-B
and PDGF-receptor b is associated with lymphatic
metastasis in human gastric carcinoma
Michiyo Kodama,1Yasuhiko Kitadai,1,4Tomonori Sumida,1Mayu Ohnishi,1Eiji Ohara,1Miwako Tanaka,1
Kei Shinagawa,1Shinji Tanaka,2Wataru Yasui3and Kazuaki Chayama1
1Department of Medicine and Molecular Science, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima;2Department of Endoscopy,
Hiroshima University Hospital, Hiroshima;3Department of Pathology, Hiroshima University Graduate School of Biomedical Sciences, Hiroshima, Japan
(Received March 15, 2010 ⁄Revised May 25, 2010 ⁄ Accepted May 28, 2010 ⁄ Accepted manuscript online June 7, 2010 ⁄Article first published online July 7,
Recent study of murine fibrosarcoma has revealed that platelet-
derived growth factor (PDGF) plays a direct role in promoting lym-
phangiogenesis and metastatic spread to lymph nodes. Thus, we
investigated the relation between PDGF and PDGF receptor (PDGF-
R) expression and lymphatic metastasis in human gastric carci-
noma. We examined PDGF-B and PDGF-Rb expression in four
human gastric carcinoma cell lines (TMK-1, MKN-1, MKN-45, and
KKLS) and in 38 surgical specimens of gastric carcinoma. PDGF-B
and PDGF-Rb expression was examined by immunofluorescence in
surgical specimens and in human gastric carcinoma cells (TMK-1)
implanted orthotopically in nude mice. Groups of mice (n = 10,
each) received saline (control) or PDGF-R tyrosine kinase inhibitor
imatinib. PDGF-B and PDGF-Rb mRNA expression was significantly
higher in patients with lymph node metastasis than in those with-
out and was also significantly higher in diffuse-type carcinoma
than in intestinal-type carcinoma. In surgical specimens, tumor
cells expressed PDGF-B, but PDGF-Rb was expressed predominantly
by stromal cells. Under culture conditions, expression of PDGF-B
mRNA was found in all of the gastric cell lines, albeit at different
levels. In orthotopic TMK-1 tumors, cancer cells expressed PDGF-B
but not PDGF-Rb. PDGF-Rb was expressed by stromal cells, inclu-
ding lymphatic endothelial cells. Four weeks of treatment with
imatinib significantly decreased the area of lymphatic vessels.
Our data indicate that secretion of PDGF-B by gastric carcinoma
cells and expression of PDGF-Rb by tumor-associated stromal cells
are associated with lymphatic metastasis. Blockade of PDGF-R
signaling pathways may inhibit lymph node metastasis of gastric
carcinoma. (Cancer Sci 2010; 101: 1984–1989)
which relies on de novo formation of blood and lymphatic ves-
sels.(1)Although induction of tumor angiogenesis is known to be
a complex process that involves the interplay of a dozen or more
tumor-derived growth factors,(2)how tumors induce lymphan-
giogenesis is poorly understood.
Among known lymphangiogenic factors, the best-character-
ized growth factors are vascular endothelial growth factor C
(VEGF-C) and VEGF-D.(3–8)Fibroblast growth factor-2 pro-
motes lymphatic vessel growth in the mouse cornea, but this
effect is believed to occur indirectly, via induction of VEGF-
C expression and activation of VEGF receptor 3 (VEGFR-3)
signaling.(9)It is unlikely that VEGF-C and -D and VEGFR-3
are the sole factors regulating such processes. A range of
lymphangiogenic factors produced by tumor cells, endothelial
cells, and stromal cells has recently been identified. These
include VEGF-A, and members of the hepatocyte growth fac-
tor (HGF) and angiopoietin (Ang) families.(10–12)Additionally,
interesting preclinical studies have indicated that platelet-
astric cancer is one of the most frequent malignancies in
the world. The major cause of mortality is metastasis,
derived growth factors (PDGFs) and PDGF receptors (PDGF-Rs)
not only promote hemangiogenesis and direct tumor cell
growth but are important players in lymphangiogenesis.(13)
Members of the PDGF family are often expressed at high lev-
els in many malignant tissues.(14)The PDGF family consists of
five isoforms, -AA, -AB, -BB, -CC, and -DD, usually referred to
as PDGF-A (AA), PDGF-B (AB and BB), PDGF-C (CC), and
PDGF-D (DD).(15)Their biological activities are mediated by
three forms of the tyrosine kinase receptor encoded by two gene
products, PDGF-Ra and -Rb. PDGF-Ra binds all possible forms
of PDGF except PDGF-DD, whereas PDGF-Rb preferentially
binds PDGF-BB.(16)PDGFs have been found to induce tumor
growth by directly stimulating growth of certain types of tumor
cells,(17)to stimulate angiogenesis,(18)to recruit pericytes(19)and
to control the interstitial fluid pressure in stroma, influencing
transvascular transport of chemotherapeutic agents in a para-
crine manner.(20)Recently, Cao et al.(13)showed that expression
of PDGF-B in murine fibrosarcoma cells induced tumor lym-
phangiogenesis, leading to enhanced lymph node metastasis.
However, there is no report concerning the relation between
PDGF-B and PDGF-Rb expression and lymphatic metastasis
in human gastric carcinoma. Thus, we examined the expression
profile of PDGF-B and PDGF-Rb in human gastric carcinoma,
and we examined whether blocking PDGF-R can inhibit lym-
phangiogenesis of gastric cancer in vivo.
Materials and Methods
Patients and tumor specimens. Endoscopic biopsy specimens
(tumor and corresponding normal mucosa) of gastric tissue from
38 patients with gastric carcinoma who later underwent surgical
resection at Hiroshima University Hospital were snap-frozen in
liquid nitrogen and stored at )80?C until RNA extraction for
quantitative RT-PCR. Informed consent was obtained from all
patients for participation in the study according to the Declara-
tion of Helsinki. Pathology reports and clinical histories were
reviewed for accurate staging at the time of surgery. Criteria for
staging and histologic classification were those proposed by the
Japanese Research Society for Gastric Cancer.(21)Lymph node
status was determined by routine pathological examination with
the surgical specimens. Two groups of patients, those with
lymph node metastasis (node-positive group, n = 21) and those
without (node-negative group, n = 17), were closely matched
for histologic type and depth of invasion. The patient group
comprised 34 men and four women with a median age of
4To whom correspondence should be addressed.
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low levels of PDGF-B (data not shown). In general, tumor cells
in a neoplasm are biologically heterogeneous, and their pheno-
type can be modified by the organ microenvironment.(30)Our
data indicate that tumor-associated lymphatic vessels are also
biologically heterogeneous and that interplay between lymphatic
vessels and tumor cells may have a more significant effect on
the endothelial phenotype than previously anticipated. Addition-
ally, blockade of PDGF-Rb signaling by oral administration of
the PDGF-R tyrosine kinase inhibitor imatinib significantly
reduced the area of lymphatic vessels in our orthotopic mouse
model of gastric cancer. In our experiment, lymph node metasta-
sis was not inhibited by treatment with imatinib alone (control,
8⁄10 vs imatinib treatment, 7⁄10). To inhibit lymph node metas-
tasis, reduction of the lymphatic vessel area seems to be
insufficient. Combination therapy of imatinib with cytotoxic
chemotherapeutic drugs may be needed to inhibit lymph node
metastasis. Together, these findings indicate that PDGF-Rb is
preferentially expressed by activated, proliferating lymphatic
endothelium but not by quiescent lymphatic vessels in normal
tissue, a finding with important implications for the potential
therapeutic use of targeted PDGF-Rb-blocking strategies.
In conclusion, we found PDGF-B secreted by tumor cells and
PDGF-Rb expressed by stromal cells including lymphatic endo-
thelial cells to be associated with lymphatic metastasis in gastric
carcinoma. Thus, blockage of PDGF-induced lymphangiogene-
sis may be a reasonable approach to prevention and treatment of
This work was carried out with the kind cooperation of the Analysis
Center of Life Science, Hiroshima University, Hiroshima, Japan, and we
thank Novartis Pharma K.K. (Basel, Switzerland) for providing the
imatinib used in the study. This work was supported, in part, by Grants-
in-Aid for Cancer Research from the Ministry of Education, Culture,
Science, Sports and Technology of Japan and from the Ministry of
Health, Labor and Welfare of Japan.
The authors have no conflict of interest.
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