Frequency of homozygous deletion at p16/CDKN2 in primary human tumours.

Many tumour types have been reported to have deletion of 9p21 (refs 1-6). A candidate target suppressor gene, p16 (p16INK4a/MTS-1/CDKN2), was recently identified within the commonly deleted region in tumour cell lines. An increasing and sometimes conflicting body of data has accumulated regarding the frequency of homozygous deletion and the importance of p16 in primary tumours. We tested 545 primary tumours by microsatellite analysis with existing and newly cloned markers around the p16 locus. We have now found that small homozygous deletions represent the predominant mechanism of inactivation at 9p21 in bladder tumours and are present in other tumour types, including breast and prostate cancer. Moreover, fine mapping of these deletions implicates a 170 kb minimal region that includes p16 and excludes p15.

Evidence for two bladder cancer suppressor loci on human chromosome 9.

Most carcinomas of the bladder show loss of heterozygosity for markers on human chromosome 9, which suggests that one or more tumor suppressor genes are located on this chromosome. Several observations suggest that such alterations are an important early step in tumorigenesis. We analyzed the pattern of allelic loss in 46 primary carcinomas of the bladder using 19 polymorphic markers from chromosome 9. While most tumors with allelic loss showed loss of heterozygosity for all informative markers that were tested, six tumors demonstrated only partial loss of chromosome 9. Two tumors with partial loss contained deletions that predominantly involved the q arm, as shown by previous studies. The other four tumors contained deletions that predominantly or exclusively involved the p arm, with a common region of loss between D9S161 (9p21) and the telomere. The results show that there is no single common region of loss on chromosome 9 and identify two distinct regions of loss that may contain bladder tumor suppressor loci.

Localization of tumor suppressor loci on chromosome 9 in primary human renal cell carcinomas.

To investigate the potential loss of tumor suppressor gene loci on chromosome 9 in human renal cell tumorigenesis we analyzed 42 paired normal and tumor DNAs with 18 polymorphic microsatellite markers spanning this chromosome. Fourteen of 42 (33%) tumors showed partial or complete deletion of chromosome 9. Deletion mapping provided evidence for the presence of a suppressor locus on both the short and long arm of chromosome 9. Homozygous deletion at 9p21-22 in one renal tumor and a selective deletion of distal 9q in another tumor localized the critical regions. The CDKN2/p16 gene was further investigated as a candidate suppressor locus on 9p21-22 by multiplex PCR, Southern analysis, and exon sequencing. We found no additional cases of homozygous deletion nor any rearrangements or point mutations of CDKN2/p16. This is the first report of 9p loss of heterozygosity, homozygous deletion of 9p21-22 and selective deletion of 9q in primary renal cell carcinomas. Understanding the molecular genetic basis of renal cell progression will require the isolation and characterization of additional tumor suppressor genes on chromosome 9.

Homozygous deletions of 9p21 in primary human bladder tumors detected by comparative multiplex polymerase chain reaction.

Deletion mapping studies of primary bladder tumors have identified nonoverlapping areas of loss on each arm of chromosome 9, indicating that two distinct tumor suppressor loci are located on this chromosome. The deleted region on the p arm overlaps an area of 9p previously reported to be lost in a variety of neoplasms. Detailed loss of heterozygosity analysis of 9p in 112 primary bladder tumors using 12 microsatellite markers identified a minimal area of loss around the alpha-interferon locus at 9p21-22. Frequent homozygous deletions of the alpha-interferon locus were then identified in these tumors by a novel, comparative, multiplex polymerase chain reaction assay and were subsequently confirmed by Southern analysis. Based on these deletions, a putative tumor suppressor gene locus involved in bladder tumorigenesis was localized to a 10 cM region (flanked by D9S162 and D9S171), previously implicated in the progression of many neoplasms. Application of the multiplex polymerase chain reaction-based assay will allow rapid identification of homozygous deletions in many neoplasms and thus aid in mapping studies of critical suppressor genes.

Frequent loss of chromosome 9p21-22 early in head and neck cancer progression.

In order to define more clearly the role of chromosome 9 loss in head and neck squamous cell carcinoma (HNSCC), 29 invasive carcinomas and 17 preinvasive lesions were analyzed for loss of heterozygosity (LOH) on chromosome 9. We found LOH in 21 of 29 (72%) HNSCC tumors using highly polymorphic microsatellite markers. In 17 of 21, LOH was found at all informative sites on the p arm with no LOH of the q arm. Further mapping in tumors, with partial LOH of the 9p arm, localized a common region of loss between markers D9S165 and D9S156. Deletion of this region on chromosome 9 has been found in several other tumor types implying the presence of a tumor suppressor gene at this locus. The inactivation of a tumor suppressor gene on chromosome 9p may represent the most commonly described genetic alteration in HNSCC. A similar incidence of allelic loss on chromosome 9p was identified in 12 of 17 (71%) preinvasive lesions. The identical frequency of loss in preinvasive and invasive lesions suggests that loss of 9p is an early event in HNSCC progression.

Progression of basal cell carcinoma through loss of chromosome 9q and inactivation of a single p53 allele.

Basal cell carcinoma (BCC) of the skin represents a unique group of tumors strongly associated with exposure to UV light. Unlike squamous carcinoma of the skin, BCC is generally indolent, noninvasive, and rarely metastatic. To study the involvement of tumor suppressor genes in these neoplasms, we analyzed 36 BCCs for p53 mutations and a subset of these tumors for loss of chromosomes 17p and 9q. Sixty-nine % of sporadic BCCs had lost a 9q allele, with the common area of loss surrounding the putative gene for nevoid BCC or Gorlin's syndrome. Forty-four % (16 of 36) of BCCs had a mutated p53 allele, usually opposite pyrimidine tracts, which is consistent with UV-induced mutations. Surprisingly, only one tumor had lost a 17p allele, and in all BCCs only one p53 allele was inactivated. This is in direct contrast to other epithelial tumors, which usually progress by the inactivation of both p53 alleles.

Microsatellite instability in bladder cancer.

Somatic instability at microsatellite repeats was detected in 6 of 200 transitional cell carcinomas of the bladder. Instabilities were apparent as changes in (GT)n repeat lengths on human chromosome 9 for four tumors and as alterations in a (CAG)n repeat in the androgen receptor gene on the X chromosome for three tumors. Single locus alterations were detected in three tumors, while three other tumors revealed changes in two or more loci. In one tumor we found microsatellite instability in all five loci analyzed on chromosome 9. The alterations detected were either minor 2-base pair changes or larger (> 2 base pairs) alterations in repeat length. All six tumors were low stage (Ta-T1), suggesting that these alterations can occur early in bladder tumorigenesis.