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A Balmain

Publications and source records attributed to A Balmain.

At least 55 records · Page 3Linked to original sources
PubMed1995

Regulatory elements in the first intron of the mouse Ha-ras gene.

The Ha-ras gene is one of the three oncogenes (Ha-ras, Ki-ras, and N-ras) of the ras superfamily of small G proteins. The p21ras proteins encoded by the ras genes are key proteins involved in the transduction of signals from membrane receptor-tyrosine kinases to downstream targets. The ras genes seem to play a ubiquitous role in the control of cell proliferation and cell differentiation. At the same time, ras genes may perform specific differentiated functions in certain cell types. Little is known about the regulation of expression of the Ha-ras gene. The first intron of the Ha-ras gene has been reported to be highly conserved between human and rodent. We investigated the role that this intron may play in the regulation of expression of Ha-ras. The promoter region of the Ha-ras gene exhibits characteristics of a housekeeping gene. Deletion analysis shows the existence of an enhancer-type element in the 5' region of the first intron (intron 0). DNase 1 footprinting experiments reveal five sites that interact with nuclear proteins from fibroblast and epithelial cell lines. Deletion and site-directed mutagenesis of three of these sites show that two are involved in a positive effect and one in a negative effect on the regulation of expression of the mouse Ha-ras gene.

3T3 Cells↗
PubMed1995

Transgenic mice and squamous multistage skin carcinogenesis.

The use of animals models of human cancers has proved useful in the elucidation of molecular events which occur during tumour development. Mouse skin has been used as a model for human squamous cancer for a number of decades, and analysis of this model has identified a number of changes important for the evolution of malignancy. Transgenic mice offer a further avenue of advancement, allowing refinement of the model, and the ability to examine the consequences of individual events in vivo in greater detail. This article reviews the impact of transgenic approaches to our understanding of multistage squamous carcinogenesis in mouse skin.

Animals↗
PubMed1995

Transgenic approaches to understanding the mechanisms of chemical carcinogenesis in mouse skin.

The use of animal models for human cancer has proved effective in the elucidation of those molecular events which are responsible for the various stages of tumour development. Chemical carcinogenesis in mouse skin has been studied as a model for human squamous cancer for several decades, and analysis of this model has led to the identification of a number of the changes which are involved in the evolution of malignancy. The use of transgenic and knockout mice offers a further avenue of advancement, allowing refinement of the model, and the ability to examine the consequences of individual events in vivo in greater detail. Additionally, crossing different transgenic or knockout animals represents a powerful tool to study the cumulative effects of several genetic alterations acting in concert.

Animals↗
PubMed1995

Distinct genetic loci control development of benign and malignant skin tumours in mice.

Genetic susceptibility to chemically induced skin cancer in mice is controlled by multiple unlinked genetic loci. Mus spretus mice have dominant resistance genes which confer resistance to interspecific F1 hybrids with susceptible Mus musculus strains. We have mapped three major resistance loci using a combination of Mapmaker/QTL analysis and multiple regression analysis to mouse chromosomes 5 and 7. At least two independent loci on chromosome 7 exert their effects primarily during benign tumour development and have very little influence on tumour progression. On the other hand, probably a single locus on chromosome 5 affects both early and late stages of malignancy. The results indicate that benign and malignant tumours are largely under independent genetic control.

Animals↗
PubMed1994

Lack of transforming growth factor-beta 1 expression in benign skin tumors of p53null mice is prognostic for a high risk of malignant conversion.

Expression of transforming growth factor beta 1 (TGF beta 1) protein was examined in chemically induced benign skin tumors with genetically defined empirical risks for malignant conversion. Benign tumors induced in mice which have both alleles of the p53 gene deleted have a malignant conversion frequency of approximately 50%, whereas similar tumors induced in wildtype and heterozygous p53 mice have conversion probabilities of 3 and 8%, respectively (Kemp et al., Cell, 74: 813-822, 1993). The TGF beta 1 antibody, anti-CC (1-30-1), was shown to stain either the proliferative keratinocyte compartment of the tumor or the tumor stroma, whereas another TGF beta 1 antibody, anti-LC (1-30-1), stained highly differentiated granular cells of the tumors. A strong correlation was found between staining of the proliferative keratinocyte compartment of tumors with the anti-CC (1-30-1) antibody and tumor genotype. Only 18% (6 of 32) of homozygous p53 null tumors showed any basal keratinocyte staining with this antibody, whereas over 80% (32 of 38) of heterozygous and wild-type tumors showed positive staining. Additionally, in most tumors examined, the spatial distribution of staining for the proliferating cell nuclear antigen appeared to be mutually exclusive with that of TGF beta 1 on adjacent serial sections. This suggests that, in these cases, tumor keratinocytes are sensitive to negative growth regulation by TGF beta. TGF beta 1 protein staining in benign tumors is thus prognostic for a low probability of malignant conversion, and its expression may be mechanistically involved in limiting malignant conversion since, at the benign tumor stage examined, keratinocytes are still sensitive to growth inhibition by TGF beta 1.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1994

An allelotype of squamous carcinoma of the head and neck using microsatellite markers.

The detection in tumors of genomic regions with a high frequency of loss of heterozygosity has led to the localization and subsequent cloning of a number of tumour suppressor genes. To identify such regions involved in the development of squamous carcinoma of the head and neck we have analyzed 28 paired normal and tumor DNA samples. Using the polymerase chain reaction to amplify 50 simple sequence repeats or microsatellite markers we have studied all 22 q limbs and 17 of the p limbs in 21 patients. In informative cases we observed a high incidence of loss of heterozygosity at five specific chromosomal regions: 3p (44%); 5q (43%); 9q (35%); 11q (45%); and 17p (31%). In addition, further analysis of tumors showing loss of heterozygosity at 5q suggests that a gene at or near the APC locus is involved in squamous carcinoma of the head and neck.

Carcinoma, Squamous Cell↗
PubMed1994

The role of p53 in spontaneous and radiation-induced apoptosis in the gastrointestinal tract of normal and p53-deficient mice.

Three h after whole-body irradiation (8 Gy) of C57BL x DBA/2 F1 mice, p53 protein was expressed strongly in the stem cell compartment of the small intestine but at lower levels in the colon. At this time, apoptotic cells were also observed in the stem cell position of the small intestine, with fewer in the colon. In mice without copies of the p53 gene (nulls), the levels of spontaneous apoptosis, in both the small intestine and the colon, were not different from wild-type. Irradiation of the nulls with 8 Gy of gamma-rays failed to induce any further apoptosis: the loss of p53 essentially rendered the epithelial cells, from both the small intestine and the colon, radioresistant. The response of the epithelial stem cells of the small intestine suggests that p53 may play a role in the deletion of damaged cells with carcinogenic potential, whereas this process is limited in the colon.

Animals↗
PubMed1994

A switch from stromal to tumor cell expression of stromelysin-1 mRNA associated with the conversion of squamous to spindle carcinomas during mouse skin tumor progression.

We previously reported that the expression of stromelysin-1 (ST-1), a matrix-degrading metalloproteinase, correlates with tumor progression in the mouse skin model of carcinogenesis. Using in situ hybridization techniques, we confirmed in this study the expression of ST-1 mRNA in mouse skin keratinocytes treated with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate and also observed dramatic expression of ST-1 message in underlying fibroblastic cells. Benign tumors formed by an initiation/promotion protocol expressed low levels of ST-1 mRNA, which was localized exclusively to stromal tissue surrounding the tumor cells. Squamous cell carcinomas, produced either by chemical carcinogenesis or by injection of cultured cells derived from chemically initiated squamous cell tumors, expressed high levels of ST-1 mRNA, which was also localized to adjacent stromal tissues. In contrast, aggressive, highly metastatic spindle cell tumors expressed ST-1 mRNA in the tumor cells as well as in normal, adjacent stroma. These results suggest that the change from ST-1 expression in surrounding stromal cells to its expression in the tumor cells themselves is associated with the conversion of squamous to spindle carcinomas and may play a causal role in the ability of these cells to invade and metastasize.

Animals↗
PubMed1994

Induction of different genetic changes by different classes of chemical carcinogens during progression of mouse skin tumors.

By analysis of skin tumors from F1 hybrid mice we demonstrated that the genetic events that occur during tumor progression depend on the type of chemical carcinogenesis protocol used to induce tumor growth. More than 95% of tumors induced by initiation with 7,12-dimethylbenz[a]anthracene (DMBA) and promotion with 12-O-tetradecanoyl-phorbol-13-acetate (TPA) exhibited mutations in Ha-ras and trisomy of chromosome 7. Carcinomas induced with multiple DMBA treatments had a lower frequency of alterations on chromosome 7 (50%), but only in tumors with Ha-ras mutations, and had a much wider spectrum of alterations, including trisomy, mitotic recombination, deletion, and gene duplication. Carcinomas induced with multiple N-methyl-N'-nitro-N-nitrosoguanidine treatments only rarely exhibited alterations on chromosome 7 (8%), even if they contained mutant Ha-ras. More frequent numerical alterations of chromosome 11 were also seen in TPA-promoted tumors (23%) than in tumors induced by multiple carcinogen treatments (8%). These results show that postinitiation events are nonrandom and fit a model in which promoting agents induce numerical chromosomal alterations but in which mutagens cause more directed mutational events.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1994

p53-deficient mice are extremely susceptible to radiation-induced tumorigenesis.

Mice constitutively lacking alleles of the p53 tumour suppressor gene spontaneously develop lymphomas and sarcomas. We report here that a single dose of 4 Gy radiation dramatically decreases the latency for tumour development in p53 heterozygous mice. The pattern of genetic alterations at the remaining wild type allele in these tumours differs substantially from spontaneous tumours from similar mice indicating that p53 itself may have been a target for radiation-induced alterations. Lower dose irradiation (1 Gy) of preweanling p53 null mice also significantly decreases tumour latency, suggesting that there are additional genetic targets involved in radiation-induced malignancy. Thus p53-deficient mice provide a sensitive model system for studies of the consequences of radiation exposure.

Animals↗
PubMed1993

Allelotype analysis of mouse skin tumors using polymorphic microsatellites: sequential genetic alterations on chromosomes 6, 7, and 11.

Allelotype analysis of human tumors has been instrumental in the effort to discover and clone novel tumor suppressor genes. However, this approach has not been systematically applied to animal models of carcinogenesis. We describe here the first attempt to allelotype a nonhuman tumor, i.e., chemically induced mouse skin tumors, using a panel of polymorphic microsatellite markers. The results indicated that markers on chromosomes 6 and 7 were imbalanced, consistent with trisomy in both benign and malignant skin tumors. A proportion of carcinomas also showed loss of heterozygosity on chromosome 11, where the p53 gene is located, and more rarely, on chromosomes 4, 6, and 15. The significance of these alterations is highlighted by the observations of no allelic imbalance for markers on 12 other chromosomes.

Alleles↗
PubMed1993

Reduction of p53 gene dosage does not increase initiation or promotion but enhances malignant progression of chemically induced skin tumors.

The availability of p53 knockout mice generated by gene targeting has enabled us to investigate the functional role of the p53 tumor suppressor gene in initiation, promotion, and progression of carcinogenesis in vivo, using mouse skin as a model system. The number, size, and growth rate of benign papillomas were not increased in the p53 heterozygous mice in comparison with wild type. The p53 null mice showed a reduced yield of papillomas, but these underwent much more rapid malignant progression, with some poorly differentiated carcinomas developing after only 10 weeks of promotion. Progression rate was also greater in heterozygous than in wild-type mice and was associated with loss of the remaining wild-type allele. Most tumors from all groups had activating mutations in the H-ras gene. Absence of p53, therefore, does not augment the frequency of initiation or the rate of promotion but greatly enhances malignant progression.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

A revised map position for the Ha-ras gene on mouse chromosome 7: implications for analysis of genetic alterations in rodent tumors.

The mouse Ha-ras gene has previously been mapped to the central region of chromosome 7, 31 cM from the centromere, using an interspecific Mus musculus/Mus spretus backcross (Saunders AM, Seldin MF, Genomics 8:525-535, 1990). However, analysis of mitotic recombinations in mouse skin tumors from intraspecific F1 hybrid mice suggested a more distal location for the Ha-ras gene on chromosome 7 (Bremner R, Balmain A, Cell 61:407-417, 1990). In the study reported here, we demonstrated, by analysis of Ha-ras gene mutations in skin tumors from interspecific M. spretus/M. musculus F1 hybrids, the existence only in M. spretus of a pseudogene or other Ha-ras-related sequence that is probably the sequence originally mapped by Saunders and Seldin. The functional Ha-ras gene maps to the distal region of chromosome 7, and it is this sequence that acquires mutations in chemically induced tumors.

Animals↗
PubMed1993

The conversion of mouse skin squamous cell carcinomas to spindle cell carcinomas is a recessive event.

Squamous carcinomas of both human and rodent origin can undergo a transition to a more invasive, metastatic phenotype involving reorganization of the cytoskeleton, loss of cell adhesion molecules such as E-cadherin and acquisition of a fibroblastoid or spindle cell morphology. We have developed a series of cell lines from mouse skin tumors which represent different stages of carcinogenesis, including benign papillomas, and clonally related squamous and spindle carcinomas derived from the same primary tumor. Some spindle cells continue to express keratins, but with a poorly organized keratin filament network, whereas in others no keratin expression is detectable. All of the spindle cells lack expression of the cell adhesion molecule E-cadherin and the desmosomal component desmoplakin. Loss of these cell surface proteins therefore appears to precede the destabilization of the keratin network. At the genetic level, it is not known whether such changes involve activation of dominantly acting oncogenes or loss of a suppressor function which controls epithelial differentiation. To examine this question, we have carried out a series of fusion experiments between a highly malignant mouse skin spindle cell carcinoma and cell lines derived from premalignant or malignant mouse skin tumors, including both squamous and spindle carcinoma variants. The results show that the spindle cell phenotype as determined by cell morphology and lack of expression of keratin, E-cadherin, and desmoplakin proteins, is recessive in all hybrids with squamous cells. The hybrids expressed all of these differentiation markers, and showed suppression of tumorigenicity to a variable level dependent upon the tumorigenic properties of the less malignant fusion partner. Our results suggest that acquisition of the spindle cell phenotype involves functional loss of a gene(s) which controls epithelial differentiation.

Animals↗