Background: CYCLIN D1, a cell-cycle control gene, recently has been shown to be identical to an oncogene alternatively known as BCL-1 and PRAD1 and implicated in centrocytic lymphomas and parathyroid adenomas, respectively. PRAD1 complexes to the product of the retinoblastoma (Rb) tumor suppressor gene, an event followed by Rb inactivation. Squamous cell carcinomas of the cervix and vulva are gynecologic tumors in which human papillomaviruses have been implicated as an initiating event, and proteins derived from these viruses also complex with an inactivate Rb. Because of the overlap in some of the molecular processes mediated by human papillomaviruses and by the PRAD1 oncogene, the authors analyzed the PRAD1 (CYCLIN D1/BCL-1) genomic structure and expression in vulvar and cervical squamous cell carcinoma cell lines.
Methods: PRAD1 DNA and PRAD1 mRNA expression were assessed by Southern and Northern blotting, respectively, in 13 squamous cell carcinoma cell lines of gynecologic origin (10, cervical cancer; 3, vulvar cancer).
Results: We found low baseline levels of a 4.5-kb PRAD1 transcript in a series of control cell lines, which were derived from normal fibroblasts, various hematologic malignancies, and a choriocarcinoma. PRAD1 mRNA overexpression (> or = 10-fold greater than that in control lines) was seen in all three vulvar carcinoma cell lines, two of which also showed amplification (5-fold and > 10-fold) of PRAD1 genomic sequences. Abnormalities of PRAD1 also were seen in 4 of the 10 cervical cancer cell lines and included overexpression of PRAD1 transcripts (3-9-fold) in 3 lines and rearrangement of PRAD1 DNA in an additional line that, however, did not shown any aberration in PRAD1 mRNA as discernible by Northern blotting. PRAD1 abnormalities were observed in three of the four cervical cell lines derived from metastatic sites and in one of the six cervical lines derived from primary tissue.
Conclusions: Seven of 13 squamous cell lines of gynecologic origin showed abnormalities of PRAD1. These abnormalities included amplification and rearrangement of DNA and overexpression of mRNA. The role of PRAD1 as a cell-cycle regulatory gene and its interactions with the Rb tumor suppressor gene suggests that PRAD1 deregulation may be a significant molecular event in the evolution of these tumors.