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A submicroscopic homozygous deletion at the D3S3 locus in a cell line isolated from a small cell lung carcinoma
P Rabbitts1, J Bergh, J Douglas
1MRC Clinical Oncology and Radiotherapeutics, MRC Centre, Cambridge, UK.
Abstract:
We have used 14 DNA probes, which detect 19 different restriction enzyme length polymorphisms, to search for heterozygosity on chromosome 3 in five cell lines isolated from patients with small cell lung carcinoma. The cell lines on karyotype analysis did not show the deletion in chromosome 3 characteristic of this disease. Our objective was to determine if allelic loss had occurred by some chromosomal mechanism other than deletion. Two of the cell lines are consistent with allelic loss having occurred by whole chromosome loss and reduplication. The third may have lost only the short arm due to i(3q) formation. The fourth cell line has an i(3q) chromosome, together with a translocation product involving the distal portion of the short arm of chromosome 3. Lack of evidence of heterozygosity for this distal portion of 3p suggests that a copy of the 3p homologue is involved in the translocation and therefore does not explain allelic loss of of the other homologue. The fifth, while also likely to have lost one chromosome homologue, has a submicroscopic deletion on all chromosome 3s, only detectable by RFLP analysis. Such homozygous deletions have recently proved useful in the isolation of tumour suppressor genes.
Insights
Small cell lung carcinoma cell lines show chromosome 3 allelic loss through mechanisms beyond deletion, including whole chromosome loss, partial arm loss, and submicroscopic deletions. These findings are crucial for identifying tumor suppressor genes.
Area of Science:
- Oncology
- Human Genetics
- Molecular Biology
Background:
- Small cell lung carcinoma (SCLC) is often associated with characteristic deletions on chromosome 3.
- Previous analyses did not reveal these deletions in the studied SCLC cell lines.
- Investigating alternative mechanisms of allelic loss on chromosome 3 is essential.
Purpose of the Study:
- To investigate allelic loss on chromosome 3 in SCLC cell lines using restriction enzyme length polymorphism (RFLP) analysis.
- To identify chromosomal mechanisms of allelic loss other than deletion in SCLC.
- To explore the potential role of these alterations in tumor suppressor gene identification.
Main Methods:
- Utilized 14 DNA probes to detect 19 restriction enzyme length polymorphisms (RELP).
- Analyzed five SCLC cell lines lacking characteristic chromosome 3 deletions via karyotype analysis.
- Applied RFLP analysis to assess heterozygosity and allelic status on chromosome 3.
Main Results:
- Two cell lines exhibited allelic loss consistent with whole chromosome loss and reduplication.
- One cell line showed potential loss of the short arm due to isochromosome 3q (i(3q)) formation.
- Another cell line presented an i(3q) and a translocation involving the distal 3p, suggesting allelic loss through translocation.
- The fifth cell line displayed submicroscopic deletions on all chromosome 3s, detectable only by RFLP.
Conclusions:
- Allelic loss on chromosome 3 in SCLC can occur through diverse mechanisms beyond simple deletion.
- Isochromosome formation and translocations are significant contributors to allelic imbalance on chromosome 3.
- Submicroscopic homozygous deletions identified via RFLP analysis offer a promising avenue for isolating novel tumor suppressor genes in SCLC.