Inducible transgenics. New lessons on events governing the induction and commitment in mammary tumorigenesis

p21-Activated kinase 1 coordinates aberrant cell survival and pericellular proteolysis in a three-dimensional culture model for premalignant progression of human breast cancer

Overexpression of p21-activated kinase 1 (PAK1) occurs during the progression of human breast cancer. We have investigated the role of PAK1 in the premalignant progression of the MCF10 series of human breast epithelial cell lines. Levels of PAK1 expression and activation increased with premalignant progression, and expression of dominant-negative (DN) PAK1 reduced both cell proliferation and migration/invasion. In three-dimensional (3D) overlay cultures in reconstituted basement membrane, the MCF10 series produced an in vitro model for premalignant progression. MCF10AneoT cells formed a hyperplastic morphology in which some spheroids developed abnormal lumens. The MCF10.AT1 line exhibited an atypical hyperplastic morphology of abnormal spheroid clusters that did not form lumens. The MCF10.DCIS cells exhibited dysplastic growth. Expression of DN-PAK1 promoted lumen formation in 3D-cultured MCF10A, NeoT, and AT1 structures, suggesting partial reversion of the premalignant phenotype, but did not affect the atypical budding of AT1 structures or the dysplastic growth of ductal carcinoma in situ structures. Aberrant proteolysis is another important characteristic of breast cancer progression and invasion. DN-PAK1 or knock-down of PAK1 reduced pericellular proteolysis of DQ-collagen IV in the 3D cultures. Treatment of cells with an inhibitor of Rac1 also reduced pericellular proteolysis, and this reduction was reversed by the expression of activated PAK1. Our conclusion is that overexpressed and activated PAK1 may be a key coordinator of aberrant cell survival and proteolysis in breast cancer progression.

Modulation of p53 and c-myc in DMBA-Induced Mammary Tumors by Oral Glutamine

Previous studies established that oral glutamine (GLN) reduced tumor development in implantable and 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer models. This finding was associated with a decrease in tumor glutathione (GSH) levels, while maintaining normal gut, blood, and breast GSH. Alterations in GSH levels contribute to the control of apoptotic and cell cycle-regulating signaling. The aim of this study was to examine the role of dietary GLN on activation of p53 and c-myc, which play critical roles in cancer development and sensitivity to radiation and chemotherapy. Mammary gland carcinomas were induced in rats by DMBA. The rats were gavaged daily with GLN or water (controls), starting 1 wk prior DMBA-application and throughout the duration of the experiment (11 wk after DMBA). Tumor DNA was examined for mutations in p53 exons 5 and 6. Protein and mRNA levels of p53, p21(WAF1/CIP1), PTEN, IGF-IR, mdm2, and c-myc in tumors of GLN-supplemented rats were compared with those of the control rats (received water). The sequencing of p53 showed that it was wild type. Increased phosphorylation of p53, as well as higher mRNA and protein levels of p21(WAF1/CIP1), PTEN, and mdm2, and lower levels of IGF-IR were detected in tumors of GLN-supplemented rats vs. controls. Both phosphorylated c-myc and c-myc mRNA levels were reduced by GLN. The up-regulation of tumor p53 signaling and down-regulation of c-myc, in addition to previously established inhibition of Akt signaling in DMBA-breast cancer model, suggest that dietary GLN could be a useful approach for increasing the effectiveness of cancer treatment.

Loss of heterozygosity of Kras2 gene on 12p12-13 in Chinese colon carcinoma patients

AIM: To study the loss of heterozygosity (LOH) on 12p12-13 in Chinese colon carcinoma patients.

METHODS: DNA was extracted from 10 specimens of cancer tissue, 10 specimens of adjacent tissue and 10 specimens of normal tissue, respectively. LOH of Kras2 gene was analyzed by polymerase chain reaction (PCR) and denaturing polyacrylamide gel electrophoresis using 11 microsatellite markers on 12p-12-13.

RESULTS: LOH of Kras gene was detected at least on one marker of 12p-12-13 in 30% (3/10) of adjacent tissue specimens. The highest frequency of LOH was identified on D12S1034 in 28.57% (2/7) of adjacent tissue specimens. LOH was detected at least on one marker of 12p12-13 in 60% (6/10) of carcinoma tissue specimens, the most frequent LOH was found on D12S1034 and D12S1591 in 42.86% (3/7) of carcinoma tissue specimens. LOH was detected in 30% (3/10) of carcinoma tissue specimens, 30% (3/10) of adjacent tissue specimens, and no signal in 1% (1/0) carcinoma tissue specimen. The occurrence of LOH did not correlate with sex, age, tumor size and lymph node metastasis.

CONCLUSION: Genomic instability may occur on 12p-12-13 of Kras2 gene in the development and progression of colon carcinoma. The high LOH of Kras2 gene may directly influence the transcription and translation of wild type Kras2 gene.

Transgenic mouse models for the prevention of breast cancer

Breast cancer prevention research has made remarkable progress in the past decade. Much of this progress has come from clinical trials. However, in the future to test the many promising agents that are now available, pre-clinical models of breast cancer are needed. Such models are now available. Useful models include rat and mouse models, particularly, the genetically engineered mice (GEM). Many transgenic mouse models have been generated by manipulating growth factors and their receptors, cell cycle regulators, signal transduction pathways, cellular differentiation, oncogenes and tumor suppressor genes. The transgenes are induced to express in the mouse mammary glands under the control of various transgenic promoters, which have respective characteristics in expression pattern and other biological attributes. These models are providing invaluable insight on the molecular mechanisms of breast tumorigenesis. In this review, we discuss the relative relevance of the most commonly used transgenic mouse models for breast cancer prevention studies, and provide examples of how these transgenic models can be used to conduct cancer prevention research. Due to the multi-factor, multi-step nature of breast cancer, many factors should be incorporated into a valid prevention study. However, many barriers to progress must be overcome, including access to and availability of new cancer preventive drugs, and difficulties in conducting studies of combinations of preventive agents.

Novel agents for the prevention of breast cancer: targeting transcription factors and signal transduction pathways

Transformation of breast cells occurs through loss or mutation of tumor suppressor genes, or activation or amplification of oncogenes, leading to deregulation of signal transduction pathways, abnormal amplification of growth signals, and aberrant expression of genes that ultimately transform the cells into invasive cancer. The goal of cancer preventive therapy, or "chemoprevention," is to eliminate premalignant cells or to block the progression of normal cells into cancer. Multiple alterations in signal pathways and transcription factors are observed in mammary gland tumorigenesis. In particular, estrogen receptor (ER) deregulation plays a critical role in breast cancer development and progress, and targeting ER with selective ER modulators (SERMs) has achieved significant reduction of breast cancer incidence in women at high risk for breast cancer. However, not all breast cancer is prevented by SERMs, because 30-40% of the tumors are ER-negative. Other receptors for retinoids, vitamin D analogs and peroxisome proliferator-activiator, along with transcription factors such as AP-1, NF-kappaB, and STATs (signal transducers and activators of transcription) affect breast tumorigenesis. This is also true for the signal transduction pathways, for example cyclooxygenase 2 (Cox-2), HER2/neu, mitogen-activated protein kinase (MAPK), and PI3K/Akt. Therefore, proteins in pathways that are altered during the process of mammary tumorigenesis may be promising targets of future chemopreventive drugs. Many newly-developed synthetic or natural compounds/agents are now under testing in preclinical studies and clinical trials. Receptor selective retinoids, receptor tyrosine kinase inhibitors (TKIs), SERMs, Cox-2 inhibitors, and others are some of the promising novel agents for the prevention of breast cancer. The chemopreventive activity of these agents and other novel signal transduction inhibitors are discussed in this chapter.