Smad4 haploinsufficiency in mouse models for intestinal cancer.

The Smad4(+/E6sad) mouse carries a null mutation in the endogenous Smad4 gene resulting in serrated adenomas and mixed polyposis of the upper gastrointestinal (GI) tract with 100% penetrance. Here, we show by loss of heterozygosity (LOH) analysis and immunohistochemistry (IHC) that, although the majority of the tumors appear at 9 months of age, somatic loss of the wild-type Smad4 allele occurs only at later stages of tumor progression. Hence, haploinsufficiency underlies Smad4-driven tumor initiation in the GI tract. As both the Apc and Smad4 tumor suppressor genes map to mouse chromosome 18, we have bred Smad4(+/E6sad) with the Apc(+/1638N) model to generate two distinct compound heterozygous lines carrying both mutations either in cis (CAS) or in trans (TAS). Strikingly, both models show increased tumor multiplicities when compared with the single mutant littermates, although CAS mice are more severely affected and became moribund at only 5-6 weeks of age. Phenotypic and molecular analyses indicate that Smad4 haploinsufficiency is sufficient to significantly affect tumor initiation and progression both prior to and upon loss of Apc function. Moreover, complete loss of Smad4 strongly enhances Apc-driven tumor formation.

The role of the APC tumor suppressor in chromosomal instability.

Colorectal cancer (CRC) still represents the model of choice to study the mechanisms underlying tumor initiation and progression. Accordingly, CRC has been central in the analysis of the role played by chromosomal instability (CIN) in tumor initiation and progression. Although loss of APC tumor suppressor function initiates the adenoma-carcinoma sequence in the vast majority of CRCs through constitutive activation of Wnt/beta-catenin signaling, the APC gene also represents a candidate CIN gene in CRC. Accordingly, two studies published in 2001 showed that truncating Apc mutations can lead to both quantitative and qualitative ploidy changes in primary mouse cell lines, mainly due to kinetochore and centrosome abnormalities. Here, we review and discuss the more recent literature on APC's functional activities possibly related to its role in eliciting CIN in tumor initiation and progression. We propose a model where loss and/or truncation of APC cause mitotic spindle defects that, upon somatic inactivation of other putative CIN genes (e.g. spindle and cell cycle checkpoint genes, DNA repair, telomere maintenance, etc.) underlie aneuploidy as observed in the majority of CRCs.

The human ROX gene: genomic structure and mutation analysis in human breast tumors.

We have recently isolated a human gene, ROX, encoding a new member of the basic helix-loop-helix leucine zipper protein family. ROX is capable of heterodimerizing with Max and acts as a transcriptional repressor in an E-box-driven reporter gene system, while it was found to activate transcription in HeLa cells. ROX expression levels vary during the cell cycle, being down-regulated in proliferating cells. These biological properties of ROX suggest a possible involvement of this gene in cell proliferation and differentiation. The ROX gene maps to chromosome 17p13.3, a region frequently deleted in human malignancies. Here we report the genomic structure of the human ROX gene, which is composed of six exons and spans a genomic region of less than 40 kb. In an attempt to identify possible inactivating mutations in the ROX gene in human breast cancer, we performed a single-strand conformation polymorphism analysis of its coding region in 16 sporadic breast carcinomas showing loss of heterozygosity in the 17p13.3 region. No mutations were found in this analysis. Five nucleotide polymorphisms were identified in the ROX gene, three of which caused an amino acid substitution. These nucleotide changes were present in the peripheral blood DNAs of both the patients and the control individuals. In vitro translated assays did not show a significant decrease in the ability of the ROX mutant proteins to bind DNA or to repress transcription of a driven reporter gene in HEK293 cells. Despite experimental evidence that ROX might act as a tumor suppressor gene, our data suggest that mutations in the coding region of ROX are uncommon in human breast tumorigenesis.

The influence of indomethacin and sulindac on some pharmacological actions of atenolol in hypertensive patients.

Indomethacin and sulindac were used as tools to study the role of renal and/or systemic prostaglandins in the pharmacological response to atenolol. Patients receiving chronic treatment with atenolol 100 mg received indomethacin 50 mg twice daily or sulindac 200 mg twice daily in a randomised crossover trial. Indomethacin significantly reduced the antihypertensive action of atenolol while sulindac had no effect. The role that systemic and/or renal prostaglandins may play in the antihypertensive action of atenolol is discussed with reference to renal PGI2 production and inhibition of platelet cyclo-oxygenase.