Related Experiment Videos
Restriction digest PCR (RD-PCR) for the analysis of gene mutations. Application to Ki-ras
K R Huber1, J Bittner, K Bauer
1Ludwig-Boltzmann Institute for Moleculargenetic Laboratory Diagnostics, Donauspital, SMZ-Ost, Vienna, Austria. Klaus.Huber@smz.magwien.gv.at
Abstract:
The Kirsten-ras (onco)gene codes for a GTP-binding membrane protein that is involved in signal transduction. Activated ras triggers a cascade of protein-phosphorylations that ultimately lead to cell proliferation. Ras-mutations are the main cause for adenocarcinomas of the pancreas besides some mutations in the tumor suppressor gene p53 and the c-erbB-2 oncogene. The site of ras mutations in pancreatic cancer is restricted to codon 12 that normally encodes a glycine. For analysis of codon-12 mutations, DNA is extracted from cells in pancreatic fluid and amplified by PCR. Because most of these cells originate from normal tissue with only a few tumor cells in the fluid, "enrichment PCR" must be utilized: In a first round of the PCR, ras sequences from all cells are amplified. By utilizing an appropriate restriction enzyme, wild-type sequences can be digested and the remaining fragments containing mutated sequences be amplified again. An artificial restriction site must be introduced by the 5'primer (...GGA CCT GGT...) for an enzyme (BstNI) (5'CC!WGG 3') to differentiate between wild-type sequence (...GGA GCT GGT...) (during amplification, the G is replaced by a C) and mutated sequences (_...GGA GCT (GTT), (CGT), (CCT), etc.). The necessary manipulations pose a considerable risk for contamination for the second round of the PCR procedure. Therefore, we considered whether it would be feasible to perform the restriction digest simultaneously with the first PCR reaction, and avoiding the second round altogether. The results of our experiments demonstrate that one tumor cell in 1000 normal cells can be determined readily, paralleling the results with the original two step-assay. The restriction enzyme used to enrich mutated sequences is stable long enough to be included into the PCR procedure. By this, wild-type sequence amplicons are digested while they are formed and mutated sequences can be enriched selectively.
Insights
This study introduces a streamlined PCR method to detect Kirsten-ras (onco)gene mutations in pancreatic cancer. The enhanced assay efficiently identifies rare tumor cells, improving diagnostic accuracy for pancreatic adenocarcinomas.
Area of Science:
- Molecular Biology
- Oncology
- Genetics
Background:
- Kirsten-ras (onco)gene mutations, particularly at codon 12, are key drivers of pancreatic adenocarcinoma.
- Detecting these mutations in clinical samples is challenging due to the low abundance of tumor cells.
- Conventional enrichment PCR requires multiple steps, increasing contamination risk and complexity.
Purpose of the Study:
- To develop a simplified, single-step PCR assay for detecting Kirsten-ras codon 12 mutations.
- To improve the sensitivity and reduce contamination risk in mutation detection for pancreatic cancer diagnostics.
Main Methods:
- A novel 'enrichment PCR' approach was designed, integrating restriction digestion with the initial amplification.
- An artificial restriction site was introduced via a 5' primer for BstNI enzyme digestion of wild-type sequences.
- The method was validated by assessing its ability to detect mutated ras sequences in a mixture of normal and tumor cells.
Main Results:
- The single-step assay successfully detected one tumor cell among 1000 normal cells.
- Results paralleled the sensitivity of the original two-step enrichment PCR method.
- The integrated restriction enzyme remained stable and effective within the PCR reaction.
Conclusions:
- A single-step PCR assay is feasible and effective for enriching mutated ras sequences.
- This streamlined method enhances the detection of Kirsten-ras mutations in pancreatic cancer.
- The approach offers a more efficient and less contamination-prone diagnostic tool for early cancer detection.