Allelic imbalance at the 5q14 locus is associated with decreased apoptotic rate in non-small cell lung carcinomas (NSCLCs). Possible synergistic effect with p53 gene alterations on apoptosis
Introduction
A number of genetic alterations have been identified by means of various cytogenetic and allelotyping methods in non-small cell lung cancer (NSCLC), which include gains and/or losses at multiple chromosomal regions [1]. Regions such as 1q, 2q, 3p, 5q, 8q, 9p, 13q and 17p exhibit a high frequency of genetic alterations in NSCLC [1], [2], [3], [4], [5], [6], [7], [8], [9], [10].
The long arm of chromosome 5 (5q) harbors two known tumor suppressor genes, the adenomatous polyposis coli (APC) and mutated in colorectal cancer (MCC) genes, located at 5q21 [11], [12], as well as a number of putative oncosuppressor genes [10], [13], [14]. The APC and MCC genes have been found frequently altered in colon cancer [2], [10], [11], but evidence indicates that alterations of these genes are also a common event in NSCLC [2], [3], [4], [6]. Fine mapping of the 5q deleted areas in lung [10], ovarian [14], gastric [15], [16] cancers and testicular germ cell tumors [17] has identified two frequently deleted loci at 5q13–14 and 5q34, besides 5q21.
Wild type (wt) p53, on the other hand, is a well established inducer of apoptosis and a major G1/S, G2/M and mitosis surveillance factor. Its expression is stimulated by various stress signals, including among others DNA damage, hypoxia and nucleotide deprivation [18], [19]. The failure of such a ‘checkpoint’ is reasonable to lead to deregulation of the cell cycle machinery. Defects of the p53 protein represent one of the most common phenomena in human malignancies including NSCLCs [1], [18].
In the present study we sought to characterize the 5q14 chromosome region by employing the D5S644 microsatellite marker in a series of 56 NSCLCs. Next, we examined the possible relationship between allelic imbalance (Alm) at this region, the kinetic parameters (proliferation activity and apoptosis) and the ploidy status of the tumors. Finally, the association of Alm at 5q14 with altered p53 status and their mutual impact on the above parameters was investigated. Our data indicate the existence of a putative TSG(s) mapped at the 5q14 chromosome locus.
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Tissue samples
A total of 56 NSCLCs and adjacent normal lung tissue were analyzed. These tumors were part of a panel of 68 NSCLCs previously investigated for a G1 phase protein network including p53 [5] (Table 1).
Ki-67
- 1.
Antibodies: for immunohistochemical analysis of Ki-67 nuclear antigen the following antibody (Abs) was used: MIB-1 (class: IgG1, mouse monoclonal, epitope: Ki-67 nuclear antigen) (Oncogene Science, Biodynamics, Greece).
- 2.
Method: immunohistochemistry was performed according to the indirect
D5S644 analysis
Alm analysis and relationship with clinicopathological parameters: LOH at D5S644 was observed in 21 out of 41 informative cases (51.2%). No significant association was noticed between the various clinicopathological data and D5S644 status (Table 2, Fig. 1).
p53 analysis
- 1.
IHC and relationship with clinicopathological parameters: expression of p53 was observed in 33 out of 55 informative cases (60%). The association of p53 with the clinicopathological parameters of the patients is summarized in Table 2. A
Discussion
The long arm of chromosome 5 (5q) represents a common target for genetic alterations in NSCLC [1]. Chromosomal deletions are frequent at 5q21, where two known TSGs APC and MCC are located [11], [12]. However, cytogenetic analysis has clearly dictated that 5q14 and 5q34 comprise two additional hot spot regions for deletion [13], [14], [15], [17]. In the present study, we have chosen the D5S644 microsatellite marker, which is ascribed to the 5q14.2–14.3 region according to the Genome Data Base
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Equally contributed.