A conditional feedback loop regulates Ras activity through EphA2.

The EphA2 receptor tyrosine kinase is frequently overexpressed in many cancers, including 40% of breast cancers. Here, we show that EphA2 is a direct transcriptional target of the Ras-Raf-MAPK pathway and that ligand-stimulated EphA2 attenuates the growth factor-induced activation of Ras. Thus, a negative feedback loop is created that regulates Ras activity. Interestingly, the expression of EphA2 and ephrin-A1 is mutually exclusive in a panel of 28 breast cancer cell lines. We show that the MAPK pathway inhibits ephrin-A1 expression, and the ligand expression inhibits EphA2 levels contributing to the receptor-ligand reciprocal expression pattern in these cell lines. Our results suggest that an escape from the negative effects of this interaction may be important in the development of cancer.

Identification of an epithelial-specific enhancer regulating ESX expression.

The Ets transcription factor, ESX, exhibits a unique pattern of epithelial-restricted expression and transactivates genes involved in epithelial differentiation and cancer. The aim of this study was to determine the underlying genetic basis for epithelial-specific expression of ESX. We have identified a 30bp ESX enhancer sequence (EES) approximately 3 kb upstream of the proximal promoter. This region displays enhancer activity in an epithelial-specific manner and deletion of this region abrogates ESX gene transcription. An EES binding protein complex (EBC) was identified through electrophoretic mobility shift assays whose degree of EES binding correlated well with endogenous ESX levels in epithelial cells and was regulated by epithelial differentiation. Understanding the regulation of this element will lend insight into mechanisms of epithelial differentiation and the etiology of breast cancer and may provide novel targets for cancer therapeutic intervention.

TBX3 and its isoform TBX3+2a are functionally distinctive in inhibition of senescence and are overexpressed in a subset of breast cancer cell lines.

TBX3 is a transcription factor of the T-box gene family. Mutations of TBX3 cause ulnar-mammary syndrome (MIM 181450) in humans, an autosomal dominant disorder characterized by the absence or underdevelopment of the mammary glands and other congenital anomalies. It recently was found that TBX3 was able to immortalize mouse embryo fibroblast (MEF) cells. In addition, TBX2, a homologue of TBX3, is active in preventing senescence in rodent cells and was found to be amplified in some human breast cancers, suggesting TBX3 plays a role in breast cancer. This study examined the function of TBX3 and its isoform, TBX3 + 2a. TBX3 + 2a differs from TBX3 in the DNA binding domain with an extra 20 amino acids produced by alternative splicing. We first examined the tissue expression and alternative splicing patterns of these two isoforms. We found that TBX3 and TBX3 + 2a are widely expressed in humans and mice, and alternative splicing could be tissue specific and species specific. Overexpression of TBX3 is able to immortalize MEF cells, whereas TBX3 + 2a shows an acceleration of senescence, a functional difference that may be explained by the fact that these two isoforms may have different downstream targets. TBX3, but not TBX3 + 2a, is able to bind to the previously identified T-box binding site in a gel shift assay. A subset of human breast cancer cell lines overexpresses TBX3. Our results indicate that TBX3 and TBX3 + 2a are functionally distinctive in inhibition of senescence of MEF cells and may play a role in breast cancer.

Genomic copy number analysis of non-small cell lung cancer using array comparative genomic hybridization: implications of the phosphatidylinositol 3-kinase pathway.

Genomic abnormalities at 348 loci encoding genes that may contribute to lung cancer transformation and progression were assessed using array comparative genomic hybridization in 21 squamous carcinomas (SqCas) and 16 adenocarcinomas (AdCas). Hierarchical clustering showed a clear pattern of gains and losses for the SqCas, whereas the pattern for AdCas was less distinct. Cross-validated classification using a K-nearest-neighbor assigned, on average, 32 of 37 samples to their proper histological subtype. The most noticeable differences between SqCas and AdCas were gain of chromosome 3q22-q26 and loss of chromosome 3p. These occurred almost exclusively in SqCas. The region of recurrent increase is approximately 30 Mb in extent, ranging from EVI1 to TFRC. PIK3CA, the alpha catalytic subunit of phosphatidylinositol 3-kinase (PI3K), is in this region. The PIK3CA copy number increase was validated using fluorescence in situ hybridization to lung cancer tissue microarrays. Activity of the downstream PI3K effector protein kinase B (PKB) was higher in SqCas than in AdCas and was correlated with PIK3CA copy number (r = 0.75), suggesting that these copy number increases contribute to activation of PI3K signaling in SqCas of the lung.