Abstract:
This study investigated molecules expressed by tumor cells used for evasion of
host immune system during the steps of colorectal tumorigenesis. These molecules
included a Receptor-binding Cancer Antigen expressed on SiSo cells 1 (RCAS1),
FasL, Transforming growth factor- (TGF)-β, Interleukin- (IL)-10, p53 mutation
protein and Human Leukocyte Antigen- (HLA)-G. Specimens from colorectal cancer
were examined for proteins and mRNA expressions by immunohistochemistry and
RT-PCR techniques. In addition, RNA in situ hybridization was performed to identify
the site of RCAS1 mRNA in the colorectal cancer specimens. The sandwich ELISA
was measured for the presence of RCAS1 protein in the serum samples. The
immunostaining and RT-PCR of RCAS1 were found in good correlation with the
clinical stages of colorectal cancer. The in situ hybridization for RCAS1 mRNA
demonstrated that RCAS1 was transcribed from the tumor cells. Positive serum
RCAS1 concentration was found at 47.5% in stage II and 37.5% in stage III and IV,
but was not found in stage I. The expression of FasL was detected in all (100%)
specimens of colorectal cancer as well as its premalignant lesions. The expression of
TGF-β was demonstrated in 41.67% (25/60 cases) of colorectal cancer specimens. IL-
10 expression was increased in the early stage of colorectal cancer but decreased in the
late stage. Although p53 mutation was positive in most cases (71.67%), the expression
was not correlated with FasL expression. Surprisingly, no expression of HLA-G was
determined in all colorectal specimens (0/85).
These results indicated that several proteins produced from colorectal cancer
play independent roles in tumor progression and tumor evasion of the immune system.