Isolation, identification and quantification of differentially expressed proteins from cancerous and normal breast...

Infiltrating ductal carcinoma (IDCA) is the most common type of breast cancer accounting for 85% of all invasive breast cancers.

Forty tissue specimens comprising 20 pairs of normal and cancerous tissues were analysed. The tissues were homogenized and proteins were extracted using phosphate buffer. The protein extracts from each pair of cancerous and normal tissue were separated using sodium dodecyl sulphate-polyacrylamide gel electrophoresis in the same gel. The protein profiles of both the tissues were compared, and the differentially expressed proteins that were detected at >70% in one or both of the tissue types were selected for protein identification analysis. Target proteins were excised and digested in situ with trypsin prior to liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis. A protein that was present in both tissue types was further quantified using extracted ions chromatogram.

The proteins were grouped as down-regulated, up-regulated and unique proteins. Twenty-two proteins were identified and eight of the proteins were found unique to cancer. These proteins belong to various molecular classes, i.e. structural protein, hypothetical protein, cytoskeletal protein, enzyme, calcium binding protein and extracellular matrix protein. One extracellular matrix protein, namely collagen alpha-1(I) chain precursor was found unique to cancer. By virtue of its location on the cell surface and its function in cancer growth, this protein may be a biomarker candidate for breast cancer.

The proteins identified in this study were present in at least 70% of the tissues tested; therefore they should have significant roles in the development of IDCA.