Promoter deletion and loss of retinoblastoma gene expression in human prostate carcinoma.

Abstract

Mutational inactivation of the retinoblastoma gene (RB) is found in all retinoblastomas and in a subset of other human neoplasms, including sarcomas of bone or soft tissue and carcinomas of lung or breast. Exogenous copies of wild-type RB have been shown to suppress the tumorigenicity of several types of tumor cells with endogenous RB mutations, including a previously described human prostatic carcinoma cell line. To further support a role for RB inactivation in the genesis ofprostate cancer, seven primary or metastatic prostate carcinoma specimens were examined for evidence of RB mutation. By the use of immunoblot analysis and immunostaining of histologic sections, RB-encoded protein was readily detected in tumor cells offive specimens, was equivocally detected in one specimen, and was apparently absent from tumor cells of one specimen. RB mutations in the latter case were precisely characterized as (I) a deletion of 103 nucleotides containing transcriptional start sites and (it) loss of the second RB allele.The 103-base-pair deletion was sufficient to abolish the promoter activity of upstream DNA sequences in a heterologous expression system. These results (i) demonstrate thatRB can be inactivated in vivo by mutation of its promoter, (ii) confirm the existence ofRB mutations in some human prostate carcinomas, and (iii) suggest the use of immunohistochemical methods to screen for RB mutations in clinical samples of common adult neoplasms. mutations, as predicted by Knudson (9). RB mutations are also found in a subset of osteosarcomas, soft-tissue sarcomas, and carcinomas of breast and lung, suggesting a broad role for RB inactivation in the genesis of human tumors (8).Finally, restoration of the normal RB gene product, ppllORB, into pp11ORB-deficient (RB-) tumor cells alters several aspects of their neoplastic phenotype, including suppression of tumorigenicity in nude mice (10, 11). Because of these properties, RB is a model for studying other candidate tumor suppressor genes.In a previous study of three human prostate carcinoma cell lines, one was found to express a mutated RB mRNA and an abnormally small RB protein that was functionally inactive in tumor suppression (11). To establish the existence of RB mutations in native prostate carcinomas, primary or metastatic tumor specimens were screened for loss of RB protein expression. Two tumors were found to have severely reduced or undetectable amounts of RB protein by immunoblot analysis and by immunostaining of histologic sections. Direct detection of mutated RB alleles is hindered by the large size (';200 kilobases) and structural complexity (27 exons) of this gene (12). Nevertheless, a detailed genetic analysis of one tumor revealed both mutations leading to RB inactivation: (i) a 103-base-pair (bp) deletion that abolished activity of the RB promoter and (ii) loss of the second normal RB allele. Prostate carcinoma is the most common cancer in men (1).

Suppressive effects of antiandrogens, finasteride and flutamide on development of prostatic lesions in a transgenic rat model

“…The SV40 Tag acts as an oncoprotein through interaction with both retinoblastoma (Rb) 28 and p53 tumor-suppressor gene products. 29,30 Loss of p53 and Rb genes has been implicated in the development of prostate cancer 31,32 and in the TRAP model, SV40 Tag expression leads to abrogation of p53 and Rb functions, predisposing these cells to genetic instability. Although the TRAP model significantly differs from human prostate cancers regarding the status of p53 and Rb until late stages, it provides a very sensitive system to measure the consequence of hormone ablation in an in vivo model and assess the efficacy of potential androgen analogs because carcinogenesis in this model is primarily androgen driven.…”

Infrequent involvement of p53 gene mutations in the tumourigenesis of Japanese prostate cancer

“…Inactivation of tumour suppressor genes by the deletion of one copy of the gene and mutational inactivation of the other can lead to uncontrollable cellular proliferation characteristic of cancer. The retinoblastoma gene (Cavenee et al, 1983;Bookstein et al, 1990), Wilms's tumour gene (Gessler et al, 1990), DCC gene (Fearon et al, 1990), neurofibromatosis I gene (Wallace et al, 1990), and p53 gene on chromosome 17p ) are among known tumour suppressor genes. Cytogenetic analysis of prostate cancer has yet to consistently show chromosomal deletions.…”

Identification of two distinct deleted regions on chromosome 13 in prostate cancer

“…The Rb1 locus is frequently deleted, and in one prostate cancer cell line a 103 bp deletion of the promoter region was observed with concomitant loss of the wild type allele, suggesting inactivation of this TSG by a two-hit mechanism (Bookstein et al, 1990;Riley et al, 1994). Furthermore, immunostaining studies have revealed that the Rb1 expression is frequently decreased or absent in a signi®cant proportion of sporadic prostate cancers (Phillips et al, 1994).…”