The BCSC-1 locus at chromosome 11q23-q24 is a candidate tumor suppressor gene

Abstract

Frequent allelic loss at human chromosome 11q23-q24 occurs in a wide variety of cancers, suggesting that this region may harbor a tumor suppressor gene. By constructing a physical map of the LOH11CR2 minimal region of loss on 11q23-q24 associated with lung and breast carcinomas, we were able to clone a hereditary translocation, t(11;12)(q23;q24), in a patient with early-onset breast cancer and family history of cancer. The breakpoint was found within 6 kb of the BCSC-1 candidate tumor suppressor gene located in the LOH11CR2 region whereas additional loss of heterozygosity (LOH) analysis in breast and ovarian tumors, including that of the patient with the t(11;12)(q23;q24), implicated the BCSC-1 locus as the primary target of deletion. Northern analysis of the BCSC-1 mRNA revealed a lack of expression in 33 of 41 (80%) tumor cell lines, and its ectopic expression led to the suppression of colony formation in vitro and tumorigenicity in vivo. These data suggest that BCSC-1 may exert a tumor suppressor activity and is a likely target of the LOH observed on 11q23-q24 in cancer.

Fig. 1.

Cloning and characterization of the constitutional translocation, t(11;12)(q24;q23), in a family with breast and brain cancer. (A Left) The constitutional t(11, 12)(q24;q23) in an individual with early onset breast cancer (III:1). Karyotype analysis was performed by using standard GTG-banding techniques and the der(11) t(11;12)(q24;q23) and der(12) t(11;12)(q24;q23) are designated by arrows. (Right) Pedigree of a family with early onset breast cancer and brain cancer with onset of 69 years of age. The proband (III:1) is indicated by an arrow whereas individuals available for molecular and cytogenetic testing are indicated with a plus sign. Identified constitutional translocation carriers are designated with t(11;12), and the obligate carriers are marked with a filled black circle. (B) Fluorescence in situ hybridization analysis of the t(11;12)(q24;q23) using the BAC clone 44d21. FITC-labeled BAC44d21 spans the translocation as shown by the presence of signals (green) present on both der(11) t(11;12)(q24;q23) and der(12) t(11;12)(q24;q23). Rhodamine-labeled (red) chromosome 12 whole chromosome probe and chromosome 11 alpha-satellite probe were used as a reference. (C) Southern blot analysis of the t(11;12)(q24;q23). A 3.2-kb aberrant EcoRI fragment (asterisks) was identified by using the 5′BRKPT probe. Confirmation of the sequence obtained from cloning of the 3.2-kb EcoRI fragment was performed by using a chromosome 12-specific probe, BRKPT12.1, derived from the aberrant sequence. (D) Northern analysis of the BCSC-1 gene. (E) LOH analysis of 11q23-q24 in an individual with early onset breast cancer and a constitutional t(11;12)(q24;q23). Six microsatellite markers from the LOH11CR2 region were used to analyze microdissected normal/tumor and peripheral blood lymphocytes (PB) DNA from individual III:1 and the somatic cell hybrid clone KCI 221 CL1 DNA. Noninformative loci are indicated by open circles, retention of heterozygosity by gray circles, and loss of heterozygosity by a filled circle. Results of the marker D11S1328 are shown and loss of the normal chromosome 11 allele is indicated by an arrow.

Fig. 2.

Molecular characterization of the BCSC-1 gene at human chromosome 11q23-q24. (A) Transcription map of the human BCSC-1 gene located within the LOH11CR2 critical region on 11q23-q24 (see Supporting Data). (B) LOH analysis of chromosome 11q23-q24 in breast and ovarian cancer. Summary of informative cases with LOH in at least one of the six loci examined. Filled black circles, loss of heterozygosity; filled gray circles, retention of heterozygosity; open circles, not informative (homozygous).

Fig. 3.

Northern blot analysis of the human BCSC-1 gene in normal and cancer-derived tissues. (A) BCSC-1 expression in normal human tissues. A probe containing the entire coding region of the BCSC-1 gene was used to detect its expression in a panel of normal tissues by Northern blotting. (B) BCSC-1 gene expression in human tumor-derived cell lines. Representative Northern blots are shown, and expected transcripts are indicated by each dash. β-Actin was used as a control.

Fig. 4.

In vivo effects of ectopic BCSC-1 expression. In vivo tumorigenicity of H460, A549, and ES-2 cells in athymic (nu/nu) mice infected with BCSC-1. Tumor volumes (mm³) of xenografts from uninfected (WT) cells or cells transduced with either EGFP alone or BCSC-1 lentiviral particles.