Mice deficient in the candidate tumor suppressor gene Hic1 exhibit developmental defects of structures affected in the Miller-Dieker syndrome

Cloning, structure, and expression of the mouse Ovca1 gene

We report the isolation of the mouse Ovca1 gene, the orthologue of human OVCA1/DPH2L1, a putative tumor suppressor associated with ovarian cancer. Mouse Ovca1 contains at least 13 exons and spans approximately 17 kb. Northern analysis showed that Ovca1 is expressed in most adult mouse tissues. The most predominant Ovca1 transcript is 2.1 kb. RT-PCR analysis demonstrated Ovca1 expression in embryos from 8.5 days postcoitum (d.p.c.) to 10.5 d.p.c., and various organs of 14.5 d.p.c. embryos. Mouse Ovca1 encodes a protein of 438 amino acids and has high identity with human OVCA1. Western blot and immunohistochemistry revealed that mouse OVCA1 is a 50-kDa protein that is predominately localized in a punctate pattern in the nucleus. Based on gene homology, structure, and expression patterns, these findings indicate that mouse Ovca1 is the orthologue of human OVCA1/DPH2L1. This study will facilitate experiments to elucidate the in vivo role of Ovca1 in cancer.

Allelic imbalance and fine mapping of the 17p13.3 subregion in sporadic breast carcinomas

Chromosome arm 17p is frequently altered in a variety of human cancers, especially in breast cancer, and allelic imbalances (AIs) in the region 17p13.1 do not always coincide with mutations in the TP53 gene. A second interval that frequently shows AIs at 17p is the chromosomal band 17p13.3. This region is suspected to harbor another tumor suppressor gene. In order to get more information concerning the pattern of AIs in 17p13.3, we performed analysis of AI of 49 breast carcinomas at 6 polymorphic loci in 17p13.3. Eighty-six percent of the tumors present AI at least at one marker in 17p13.3. Among all loci tested, the highest percentage of Al was observed at loci D17S5 (77%) and D17S1528 (72%). According to these results, a minimal region of deletion could be determined between the markers D17S28 and D17S5. Fine mapping of this region revealed that the size of the deleted region is about 100-150 kb. Furthermore, a subset of the patients shows two other areas with AI close to the markers D17S1574/D17S513 and D17S849, respectively.

Identification in the human candidate tumor suppressor gene HIC-1 of a new major alternative TATA-less promoter positively regulated by p53

HIC-1 (hypermethylated in cancer 1), a BTB/POZ transcriptional repressor, was isolated as a candidate tumor suppressor gene located at 17p13.3, a region hypermethylated or subject to allelic loss in many human cancers and in the Miller-Dieker syndrome. The human HIC-1 gene is composed of two exons, a short 5'-untranslated exon and a large second coding exon. Recently, two murine HIC-1 isoforms generated by alternative splicing have been described. To determine whether such isoforms also exist in human, we have further analyzed the human HIC-1 locus. Here, we describe and extensively characterize a novel alternative noncoding upstream exon, exon 1b, associated with a major GC-rich promoter. We demonstrate using functional assays that the murine exon 1b previously described as coding from computer analyses of genomic sequences is in fact a noncoding exon highly homologous to its human counterpart. In addition, we report that the human untranslated exon is presumably a coding exon, renamed exon 1a, both in mice and humans. Both types of transcripts are detected in various normal human tissues with a predominance for exon 1b containing transcripts and are up-regulated by TP53, confirming that HIC-1 is a TP53 target gene. Thus, HIC-1 function in the cell is controlled by a complex interplay of transcriptional and translational regulation, which could be differently affected in many human cancers.

Physical and transcriptional mapping of the 17p13.3 region that is frequently deleted in human cancer

Studies of chromosomal losses at 17p13 have suggested the presence of at least two distinct regions for tumor suppressor genes, the TP53 region at 17p13.1 and a more distal region at 17p13.3. Within the latter region, Hypermethylated in Cancer 1 (HIC1) is located, a likely candidate for a tumor suppressor gene that has also been suggested to play a role in the pathogenesis of Miller-Diecker syndrome (MDS). However, single-gene isolation efforts have retrieved additional genes from 17p13.3 that could play a role in tumorigenesis. This indicates that the full potential of this chromosomal region with respect to disease-related genes has not yet been exhausted and that there may exist still unknown genes that contribute to tumorigenesis or to the complex MDS phenotype. To provide a basis for the systematic isolation and evaluation of such genes, we established a physical map over 1.5 Mb of 17p13.3 and assigned 29 transcriptional units within this region.