Breast cancer. Cyr61 is overexpressed, estrogen-inducible, and associated with more advanced disease.

To identify genes involved in breast cancer, polymerase chain reaction-selected cDNA subtraction was utilized to construct a breast cancer-subtracted library. Differential screening of the library isolated the growth factor-inducible immediate-early gene Cyr61, a secreted, cysteine-rich, heparin binding protein that promotes endothelial cell adhesion, migration, and neovascularization. Northern analysis revealed that Cyr61 was expressed highly in the invasive breast cancer cell lines MDA-MB-231, T47D, and MDA-MB-157; very low levels were found in the less tumorigenic MCF-7 and BT-20 breast cancer cells and barely detectable amounts were expressed in the normal breast cells, MCF-12A. Univariate analysis showed a significant or borderline significant association between Cyr61 expression and stage, tumor size, lymph node positivity, age, and estrogen receptor levels. Interestingly, expression of Cyr61 mRNA increased 8- to 12-fold in MCF-12A and 3- to 5-fold in MCF-7 cells after 24- and 48-h exposure to estrogen, respectively. Induction of Cyr61 mRNA was blocked by tamoxifen and ICI182,780, inhibitors of the estrogen receptor. Stable expression of Cyr61 cDNA under the regulation of a constitutive promoter in MCF-7 cells enhanced anchorage-independent cell growth in soft agar and significantly increased tumorigenicity and vascularization of these tumors in nude mice. Moreover, overexpression of Cyr61 in MCF-12A normal breast cells induced their tumor formation and vascularization in nude mice. In summary, these results suggest that Cyr61 may play a role in the progression of breast cancer and may be involved in estrogen-mediated tumor development.