Genome Scanning Detects Amplification of the Cathepsin B Gene ( CtsB ) in Transformed Rat Ovarin Surface Epithelial Cells

Objective TO isolate a portion of the amplicon inferred to be present in a malignant rat tumor cell line, NuTu 26, by the presence of a homogeneously staining chromosomal region (hsr) and identify genes embedded within it. Methods Genome scanning was used to identify an EcoRI fragment (8.6 kbp) within the amplified region of the NuTu 26 genome using a recently identified rat repetitive sequence, OST 17 as a probe. The 8.6 kbp amplified fragment was sequenced and used as starting material to obtain additional sequence information by screening a P1 clone-derived DNA library to identify any genes likely embedded in the amplicon. Use of the microdissected hsr as a probe for fluorescence in situ hybridization (FISH) and application of Southern, Northern, and Western blot analysis confirmed the amplification of this region in the NuTu 26 genome. Results The cathepsin B gene was within the amplicon of the hsr-containing marker chromosome of NuTu 26. FISH analysis and chromosomal banding further revealed that the marker chromosome was a derivative of chromosomes 4 and 15, ie, der(15)t(4;15). Conclusion Cathepsin B gene amplification may contribute to some aspect of the biology of ovarian cancer. This concept is strengthened by the finding that the gene is overexpressed frequently in independently transformed rat ovarian surface epithelial cells. (J Soc Gynecol Invest 1999;6:32–40)