African-American women have a higher risk for developing triple-negative breast cancer (TNBC). Lacking the expression of receptors for estrogen and progesterone, and without human epidermal growth factor 2 receptor gene amplification, TNBC is a very aggressive type of breast cancer with a high likelihood of metastasis and recurrence. Specific therapeutic targets for this aggressive disease remain to be identified. Phosphorylation, a post-translational modification that adds one or more phosphate groups to a protein, plays a key role in the activation and deactivation of a protein's cellular function. Here we report the first systematic phosphoproteomic analysis of a benign breast tissue, a primary breast cancer tissue, and a metastatic breast cancer tissue from the same African-American woman. Differential phosphoprotein levels were measured with a reversed-phase nano-liquid chromatograph coupled to a hybrid linear quadrupole ion trap/Fourier transform ion cyclotron resonance mass spectrometer (LC-LTQ/FT-ICR MS). Five proteins are found to be highly phosphorylated in the metastasis site of a triple negative breast cancer patient, e.g. hepatoma-derived growth factor and Isoform HMG-Y of high mobility group protein HMG-I/HMG-Y. Six proteins are found to be highly phosphorylated in the primary cancer site of a triple negative breast cancer patient, e.g. isoform 2 of transcription intermediary factor 1-beta and isoform 1 of clathrin heavy chain 1. Identified phosphoproteins are known to be involved in breast cancer signal transduction pathways. For example, the decrease in sumoylation by doxorubicin of isoform 2 of transcription intermediary factor 1-beta (TRIM28) protein was reported to be essential to induce p21 expression, and thus cell growth inhibition in MCF-7 breast cancer cells. In patients with invasive breast cancers, the co-expression of heat-shock protein (HSP) 90 alpha with an overexpressed kinase, or along with the loss of a phosphatase and tensin homologue deletion on chromosome 10, is a putative molecular prognostic marker to predict early relapse. Moreover, HSP90-alpha, which is expressed extracellularly from breast cancer cells, interacts with matrix metalloproteinase-2 (MMP2). This interaction promotes MMP2 activation, which is crucial for tumor invasiveness. HSP90-alpha is also involved in several signal pathways related to breast cancer. These results may identify new diagnostic biomarkers and therapeutic targets for TNBC. (This work was supported by grant BCTR0504465 from the Susan G. Komen for the Cure Breast Cancer Foundation, grants from the Florida Breast Cancer Coalition Research Foundation, and the Florida State University to Prof. Q.-X. Sang and by NSF Division of Materials Research through DMR-0654118 and the State of Florida to Prof. Alan G. Marshall. We also acknowledge the Cooperative Human Tissue Network Southern Division, University of Alabama at Birmingham, from which we obtained the tissues for this project.)
Citation Information: Cancer Epidemiol Biomarkers Prev 2011;20(10 Suppl):A57.