Overexpression of p53 in prostate carcinoma is associated with improved overall survival but not predictive of response to radiotherapy

p53 gene mutations are among the most common specific genetic alterations in human cancer. Inactivation of p53 and subsequent protein accumulation has been implicated in a variety of human malignancies and associated with prostate cancer progression. In this study, we assessed p53 protein overexpression and gene mutations in prostate carcinoma and investigated associations between p53 alterations and clinicopathological parameters, survival, and response to radiotherapy. We evaluated 58 archival formalin-fixed, paraffin-embedded prostate carcinomas to detect abnormal p53 nuclear protein accumulation using immunohistochemistry. p53 mutational status of tumor DNA was evaluated using polymerase chain reaction-single-strand conformation polymorphism analysis of exons 5-9 and confirmed by direct DNA sequencing. Univariate and multivariate statistical analysis was used to determine the association of p53 status with clinical characteristics and response to radiotherapy. Overexpression of p53 was detected in 42 (72%) of 58 primary prostate carcinomas, but was undetectable in 7 samples of benign prostatic hyperplasias or 5 samples of normal prostate tissue. p53 exon 5-9 mutations were detected in 8 (14%) of 58 patient specimens. p53 mutational status, but not overexpression, was associated with higher Gleason scores (p=0.0145). Neither p53 overexpression nor mutation was associated with clinical stage, biochemical disease-free probability, or predictive of response to radiotherapy. p53 protein accumulation was inversely associated with improved overall survival (p=0.0108). Our studies demonstrate that p53 protein accumulation is a frequent alteration in prostate cancer. The disparity between p53 protein overexpression and p53 exon 5-9 mutations suggests the possibility of mutations outside this region or stabilization of wild-type p53 by alternative mechanisms. In our patient population, p53 protein overexpression or mutational status was not predictive of outcome in patients treated with radiation therapy. Additional studies are needed to further evaluate the association between p53 protein overexpression and improved overall survival.

Amplification and expression of EMS-1 (cortactin) in head and neck squamous cell carcinoma cell lines

Amplification of chromosome 11q13 DNA sequences is detected in approximately 30% of primary head and neck squamous cell carcinomas (HNSCC). The amplified region includes genes for cyclin D1, hst-1, int-2, and more recently, ems-1. Ems-1 encodes an 80/85kd cytoskeletal associated protein termed cortactin, which has been shown to bind F-actin and is a pp60src substrate. We investigated 16 HNSCC cell lines for ems-1 DNA amplification and gene expression by western blotting and immunofluorescence using mAb 4F11. Amplification of ems-1 DNA was detected in 8/16 (50%) cell lines and was related directly to over-expression of cortactin by western blotting and immunofluorescence. Western blotting detected both forms of cortactin, p80 and p85, at equal intensity. Immunofluorescent staining revealed low levels of cortactin localized to the cytoplasm and surface membrane in normal bronchial epithelial cells and tumor cell cultures with single copy ems-1 DNA. In contrast, tumor cell cultures with ems-1 DNA amplification demonstrated intense, homogeneous cortactin cytoplasmic staining. These results suggest that overexpression of p80/85 may be a useful marker to identify 11q13 amplification, a molecular alteration correlated with the presence of lymph node metastasis in head and neck cancer.

Frequent p53 mutations in head and neck cancer

Squamous cell carcinomas of the head and neck (SCCHN) are associated strongly with the use of tobacco and alcohol, but little is known about the molecular pathogenesis of these tumors. In the present study, we analyzed SCCHN for mutations in the tumor suppressor gene p53 by immunocytochemistry and complementary DNA sequencing. Overexpression of p53 protein was detected in 13 (100%) of 13 SCCHN cell lines and in tumor cells cultured directly from 10 (77%) of 13 patients with SCCHN. Direct evidence for p53 mutations was obtained by sequencing p53 complementary DNA from eight SCCHN cell lines and two tumor xenografts. The genetic alterations included seven missense mutations resulting in single amino acid substitutions, a mutation encoding a stop codon, one 10-base pair deletion, and one 2-base pair addition. All seven missense mutations were G to T transversions, five of which were clustered at codons 245 and 248. A similar high frequency of G to T transversions predominates in lung cancer, another tobacco-related disease. Mutation of the p53 gene is the most common genetic alteration detected in SCCHN and implicates this gene locus as a critical site of specific damage by mutagenic carcinogens in tobacco, one of the important risk factors in the etiology of this disease.