To understand the relevance of p53 missense mutations in vivo, we generated a mouse containing an arg-to-his substitution at p53 amino acid 172, which corresponds to the R175H hot-spot mutation in human tumors by homologous recombination. Inadvertently, this mouse contains the additional deletion of a G nucleotide at a splice junction that attenuates levels of mutant p53 to near wild-type levels. Mice heterozygous for the mutant allele differed from p53 ؉͞؊ mice in tumor spectrum, with a significant increase in the number of carcinomas and a slight decrease in the number of lymphomas. More importantly, the osteosarcomas and carcinomas that developed in these mutant mice frequently metastasized (69% and 40%, respectively). In contrast, metastasis is rare in osteosarcomas of p53 ؉͞؊ mice. Loss of heterozygosity studies of tumors indicated loss of heterozygosity in only 1 of 11 tumors. These data indicate clear differences between a p53 missense mutation and a null allele in tumorigenesis in vivo and suggest that the p53R172H⌬g mutant represents a gain-of-function allele. M utations in the p53 tumor suppressor are common in the etiology of many tumors and disrupt the ability of p53 to induce growth arrest or apoptosis. In particular, the R175H mutation corresponds to one of six hot spot mutations in p53 and accounts for Ϸ6% of the missense mutations identified in human cancers (1).Mutant p53 proteins containing missense mutations have been studied in various assays, leading to suggestions that some may yield gain-of-function or dominant negative phenotypes. For example, expression of mutant p53 in p53 null cells yields tumors in syngeneic mice (2) and makes established cells highly tumorigenic (3). When assayed in comparison to other mutants, the p53R175H mutant was always the most detrimental (4-7). The p53R175H mutant cooperates better than any other mutant in ras-mediated transformation (4, 5). Cells expressing the p53R175H mutant are the most tumorigenic, as measured by growth in soft agar (6). In another experiment, genomic instability was measured in fibroblasts derived from Li-Fraumeni syndrome patients heterozygous for the p53R175H mutant (8). These cells exhibited a disrupted spindle checkpoint control and accumulated a polyploid DNA content as compared with cells with other p53 missense mutations, which arrest with a 4n DNA content. These data, coupled with the fact that most p53 mutations (Ͼ80%) occurring in human tumors are missense mutations, suggest that cells with p53 missense mutations have a growth advantage.These in vitro experiments, however, cannot assay the effect of mutant p53 on tumor growth rate, survival, and tumor spectrum in vivo. The generation of mice null for p53 (9, 10) has yielded a plethora of data as to the importance of p53 in vivo. Mice heterozygous or homozygous for a p53 null allele are predisposed to multiple tumor types such as lymphomas, sarcomas, and other tumors resembling to some extent the types of tumors seen in the Li-Fraumeni syndrome. Thymocytes from mice lacking p53...

Adolescent idiopathic scoliosis is a genetic disorder of unknown etiology. Scoliosis is a clinical feature of inherited connective-tissue disorders including Marfan syndrome. Mutations within the gene of FBN1 (fibrillin 15), a component of the extracellular matrix, are now linked to Marfan syndrome and similar clinical phenotypes. This study investigated the potential association of structural genes encoding for extracellular matrix components of FBN1, elastin, and one of the polypeptides of type-I collagen (COL1A2) with familial adolescent idiopathic scoliosis. Eleven pedigrees, including 96 individuals, were identified in which adolescent idiopathic scoliosis segregated in an apparent autosomal dominant pattern. Fifty-two individuals were determined to be affected with scoliosis. Genomic DNA was analyzed by genetic linkage utilizing four intragenic markers for the structural genes of FBN1, elastin, and COL1A2. Collectively, our results exclude the structural genes of FBN1, elastin, and COL1A2 as candidate genes within these families. However, when viewed individually, specific markers cannot be excluded within all of the families. This information complements previously reported data that fibrillin production and matrix incorporation from scoliotic fibroblasts in vitro are normal in more than 80% of patients studied.

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