Tumorigneesis has long been thought to be a multistep process, however recently it become possible to identify the molecular events as genetic and hereditery alterations that underlying the initation and progress in human colorectal cancers. The
genetic
and hereditery alterations such as gene amplication, point mutation, allelic loss of tumor suppressor gene, change of oncogene products have been studied and reported recently. Among those genetic alterations, the point mutation of ras oncogene
is
thought to be one of the most important event during colorectal tumorigenesis.
There are reports that about 11 kinds of ras oncogene pint mutation codon 12, 13 and 61 are detected. The frequency of mutation is 40%-50% in colorectal cancers and is related with metastatic acquisition, location of tumors, stage of disease but
not
with tumor cell differentiation. Detection of ras oncogene point mutation has been known that it is very complicated and difficult procedures. But after using polymerase chain reaction(PCR), procedures are simplified and less time consumed.
In order to detect ras oncogene point mutation in colorectal cancers, authors developed new methods using paired PCR of DNA samples following agarose gel electrophoresis after conforming by dot blot test of PCR-DNA with synthetic oligonucleotide
probe
tailing with digoxigenin-11-dUTP and terminal transferase. With this method, 30 cases of colorectal cancer tissues and 10 cases of normal colonic mucosa were examined the frequency of point mutations on codon 12 of ras oncogene and analysed the
relation
with stage of disease, location of tumors, lymph node metastasis and tumor cell differentiation.
@ES The obtained results were as follows:
@EN 1) The dot blot test for PCR-DNA which were positive by gel-electrophoresis by synthetic oligonucleotide probe-I and II revealed positive results in each 5 cases of primer-I and primer-II positive PCR-DNA from colorectal cancer tissues.
2) The DNA labeling method with nonradioacive dignoxigenin-11-dUTP by tailing with terminal transferase and dot blot by digoxigenin detection method are considered relatively simple, less time consumed and sensitive methods.
3) The incidence of four point mutation of ras oncogene in colorectal cancer tissues was 66.7%(20/30 cases ) and distribution was GGT GAT 26.7%, GGT-AGT 23.3%, GGT-TGT 23.3%, GGT-GTT 30.0%.
4) The frequency of point mutation by Dukes' stage was 81.8% in Dukes' B, 60.0% in Dukes'C and 50.0% in Dukes' D which revealed more frequent detection in early stage of disease. But there was no relation with tumor cell differentiation On the
other
hand, the incidence by location was 90% form above sigmoid olon, 72.7% from sigmoid colon and 33.3% in rectum which revealed decreasing frequency from proximal colon to distal rectum.
With above results authors concluded that the point mutation of ras oncogene is considered to be an important genetic event during colorectal tumorigenesis and the paired PCR and gel electrophoresis method to detect mutations is relatively
simple,
less
time consumed and sensitive method.
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