Y chromosome loss and rearrangement in non-small-cell lung cancer

While loss of the Y chromosome from the karyotype of tumor cells has frequently been found in a number of human malignancies of different types, structural alterations are a much less common finding. Prompted by the high frequency of cytogenetic Y chromosome loss found in primary non-small-cell lung cancer (NSCLC), and the fact that NSCLC karyotypes usually contain marker chromosomes of unidentified origin, we have determined the Y chromosome status of 12 NSCLC samples (7 cell lines and 5 primary tumors) at a molecular level. Of the 9 cases which did not have a cytogenetically detectable Y chromosome, 4 were negative for all the Y sequences tested. The other 5, in contrast, retained some Y chromosome sequences. In 1 case (H520), only Yq heterochromatic sequences were detected, whereas in the remaining 4 (L162, L93, L125 and L71) both Yq heterochromatic sequences and Y euchromatic sequences were retained. The region of common overlap for loss of Y euchromatin was Yp distal to the Y centromere. We hypothesize that deletion of Yp sequences may play a role in tumor progression in NSCLC due to loss of a tumor-suppressor gene.

Co-amplification of the gene for parathyroid hormone-related protein (PTHRP) and KRAS2 in a human lung cancer cell line

Parathyroid hormone-related protein (PTHRP) is expressed in a large number of tumors and is the mediator of parathyroid hormone-like effects seen in humoral hypercalcemia of malignancy. The gene coding for PTHRP has been localised to the short arm of chromosome 12. This is at the same region as the oncogene KRAS2, and amplification of KRAS2 has previously been found in human lung cancer. The BEN cell line which is known to express PTHRP was established from a patient who had squamous cell carcinoma of the lung with hypercalcemia. Cytogenetic analysis of the BEN cell line revealed a very complex karyotype with many marker chromosomes. Chromosomal in situ hybridization with biotinylated DNA probes visualized by a biotin-streptavidin-polyalkaline-phosphatase complex was used to analyse two dicentric marker chromosomes containing homogeneously staining regions (hsr) in BEN. The hsr were found to contain amplified PTHRP and KRAS2 at levels of 30-fold and 14-fold per cell, respectively. The higher level of amplification of the PTHRP gene would suggest that PTHRP is the target gene of amplification in the amplicon. This is the first report of gene amplification of PTHRP and in addition its co-amplification with KRAS2.

Molecular deletion of 9p sequences in non-small cell lung cancer and malignant mesothelioma

Previously we have reported non-random cytogenetic abnormalities involving the short arm of chromosome 9 (9P) in the majority of primary non-small cell lung cancer (NSCLC) patient samples, which indicated loss of DNA sequences. In another lung tumor, pleural malignant mesothelioma (MM), cytogenetic changes also include apparent deletions of 9p. To define the location and extent of deletions of 9p in NSCLC and MM, Southern blot analyses on six NSCLC and five MM cell lines using molecular probes to 9p loci (IFNA, IFNB1, D9S3, and D9S19) were performed, and DNA dosage was determined by densitometry. Our data demonstrated reduced dosage of 9p sequences in three of six NSCLC and four of five MM lines. A homozygous deletion of D9S3 was found in one NSCLC and one MM cell line. The region of common loss overlapped the D9S3 locus and was flanked by the IFNB1 and D9S19 loci. IFNB as previously been localized to 9p22, and the D9S3 and D9S19 loci have been mapped in this study by in situ hybridization to 9p21 and 9p13, respectively. We hypothesize the existence of one or more tumor suppressor genes on 9p with a role in the development or progression of NSCLC and MM.