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 reversed-phase nano-liquid chromatography coupled to a hybrid linear quadrupole ion trap/Fourier transform ion
cyclotron resonance mass spectrometer (LC-LTQ/FT-ICR MS). Five
proteins were found to be highly phosphorylated in the metastatic site whereas six
proteins were highly phosphorylated in the
cancer site of the TNBC patient. Identified
phosphoproteins are known to be involved in
breast cancer signal transduction pathways and these results may identify new diagnostic and therapeutic targets for TNBC.