Upregulation of HER2/ErbB2/Neu occurs in 15-30% of human breast cancers and correlates with poor prognosis. Identification of ErbB2/Neu transcriptional targets should facilitate development of novel therapeutic approaches. Development of breast cancer is a multistep process; thus, to identify the transcriptomes associated with different stages of progression of tumorigenesis, we compared expression profiles of mammary tumors and preneoplastic mammary tissue from MMTV-Neu transgenic mice to expression profiles of wild-type mammary glands using Affymetrix microarrays. We identified 324 candidate genes that were unique to ErbB2/Neu-induced tumors relative to normal mammary gland tissue from wild-type controls. Expression of a subset of these genes (82) was also changed in the preneoplastic mammary glands compared to wild-type controls, indicating that they may play a pivotal role during early events of ErbB2/Neu-initiated mammary tumorigenesis. Further analysis of the microarray data revealed that expression of several known transforming growth factor (TGF)-β target genes was altered, suggesting that the TGF-β signaling cascade is downregulated in ErbB2/Neu-induced tumors. Western blot analysis for TGF-β-Receptor-I/ALK5 and immunohistochemistry for TGF-β-Receptor-I/ALK5 and phosphorylated/activated Smad2 confirmed that the Smad-dependent TGF-β signaling cascade was inactive in these tumors. Although absent in most of the tumor, phosphorylated Smad2 was present in the periphery of tumors. Interestingly, presence of phosphorylated/activated Smad2 correlated with expression of ActivinReceptor-IB/ALK4, suggesting that although Smad-dependent TGF-β signaling is absent in ErbB2/ Neu-induced tumors, Activin signaling may be active at the leading edge of these tumors. Cumulatively, these data indicate that the TGF-β pathway is intrinsically suppressed in ErbB2/Neu tumors via a mechanism involving loss of TGF-β-Receptor-I/ALK5.

A baseline pediatric patch test panel was established through working group consensus.

The LIM-only protein, LMO4, is a transcriptional modulator overexpressed in breast cancer. It is oncogenic in murine mammary epithelium and required for G2/M progression of ErbB2-dependent cells as well as growth and invasion of other breast cancer cell types. However, the mechanisms underlying the oncogenic activity of LMO4 remain unclear. Herein, we show that LMO4 is expressed in all breast cancer subtypes examined and its expression level correlates with the degree of proliferation of such tumors. In addition, we have determined that LMO4 silencing induces G2/M arrest in cells from various breast cancer subtypes, suggesting LMO4 action in the cell cycle is not restricted to a single breast cancer subtype. This arrest was accompanied by increased cell death, amplification of centrosomes and formation of abnormal mitotic spindles. Consistent with its ability to positively and negatively regulate the formation of active transcription complexes, overexpression of LMO4 also resulted in an increase in centrosome number. Centrosome amplification has been shown to prolong the G2/M phase of the cell cycle and induce apoptosis, thus we conclude that supernumerary centrosomes mediate the G2/M arrest and cell death in LMO4-deficient cells. Furthermore, the correlation of centrosome amplification with genomic instability suggests that the impact of dysregulated LMO4 on the centrosome cycle may promote LMO4-induced tumor formation.