S100S PROTEIN EXPRESSION IN A LARGE SAMPLE-SET OF BREAST CANCER TISSUES

Abstract

S100 proteins are low molecular weight proteins ranging in size from 9 to 13 kDa. They form homo- and heterodimers and even oligomers and are expressed in tissue and cell-specific manner [1]. It is well documented, infact, that S100 proteins have a broad range of intracellular and extracellular functions. Intracellular functions include regulation of protein phosphorylation, enzyme activity, calcium homeostasis, regulation of cytoskeletal components and regulation of transcriptional factors, so they are involved in several biological processes including cell cycle regulation, cell growth, cell differentiation, and motility [2]. Extracellularly they act in a cytokine like manner through the receptor for advanced glycation end products (RAGE). In consideration of the critical roles played by S100 proteins in such large spectrum of biological activities, is not surprising that improper expression of S100 members is correlated with many pathologies and especially with cancer. A number of S100 proteins have been shown to interact with oncogenes and various proteins involved in cancer progression, including p53, cytoskeletal proteins, MMPs, and others [3,4]. In this study we aimed to perform a large-scale proteomic investigation on breast cancer patients for the screening of multiple forms of S100 proteins. The 100 surgical tissues of ductal infiltrating breast cancer utilized were collected between 2003 and 2007 in the Breast Unit of the La Maddalena Hospital. Tissue extracts were submitted to proteomic preparations for2D-IPG and protein identification was performed by peptide mass finger printing. The S100 protein members identified in different proteomic maps were: S100A2 (protein S-100L), S100A4 (metastasin), S100A6 (Calcyclin, Prolactin receptor-associated protein), two isoforms, S100A7 (psoriasin), two isoforms, S100A8 (Calgranulin-A), S100A11 (Calgizzarin), three isoforms and S100A13 (S100 calcium-binding protein A13) (Fig. 1). Our results have shown that the majority of S100 proteins were present at very low levels, if not absent, in the nontumoral tissues adjacent to the primary tumor. Moreover, we showed that some S100 protein members were ubiquitously expressed in almost all patients, while others appeared more sporadic among the same group of patients. The Association analysis of S100 members with tumor variables (age, tumor size, nodal status, immuno-cytochemical, presence of HER-2, oestrogen receptors, progesterone receptor, and Ki67), showed no significant correlations of except for S100A6 (isoform b) and S100A13 correlating with Ki67. More interestingly, patients which developed distant metastases after a three year follow-up showed a general tendency of higher S100 protein expression, compared to the disease-free group. The most robust correlation with metastasis regarded primarily the protein S100A4, and secondly the protein S100A7. We believe that this information may substantially contribute to the progress of protein profiling of breast cancer and help to organize subclasses for clinical applications.