Solatycka et al. expressing cells. Specific-reactivity of clone 7E51C83A10 mAbs towards ST3Gal-I was also confirmed by immunoblotting. Therefore, FR 180204 our observations warrant evaluation of ST3Gal-I as a potential marker TPOR for cancer diagnosis at larger scale. 1. Introduction Glycosylation is a common posttranslational modification of proteins and lipids within a cell with covalent addition of carbohydrate side chains. Altered glycosylation is very well implicated in cancer and, due to highly complex structure of sugar moieties and oligosaccharide chains, these molecules therefore give rise to large proteomic diversity. FR 180204 In recent years different methods have been developed to characterize and analyze them but still remain in their infancy [1, 2]. Accurate and precise addition of sugars is mediated by two enzymes critical for glycosylation known as glycosyltransferases and glycosides which are precisely and differentially expressed in various cells and tissues [3, 4]. Sialic acids are neuraminic acid residues located at terminal position of sugars in glycans and are often found linked to protein or lipid molecules. These molecules play an important role in cellular signaling during tumor formation, differentiation, and progression, which is brought about by the activity of enzymes belonging to the sialyltransferase family [5, 6]. Sialyltransferases are categorized into 4 families on the basis of the carbohydrate side chain they synthesize, namely, ST3Gal (2, 3-ST), ST6Gal (2, 6-ST), ST6GalNAc, and ST8Sia (2, 8-ST) [4]. Each sialyltransferase utilizes a specific sugar moiety as a substrate to catalyze the transfer of sialic acid to the oligosaccharide. The ST3Gal-I and ST3Gal-II utilize the type 3 oligosaccharide structure Gal?13GalNAc-R whereas the ST3Gal-III, ST3Gal-IV, ST3Gal-V, and ST3Gal-VI use the oligosaccharide isomers Gal?13/4GlcNAc-R [7C9]. Aberrant glycosylation is one of the major trademarks of cancer and the most common aberrant glycosylation in cancer is described in pathway of Thomsen-Friedenreich-related antigens which includes Thomsen-nouveau antigen (Tn), Sialyl-Thomsen-nouveau antigen (STn), Thomsen-Friedenreich antigen (T), and Sialyl-Thomsen-Friedenreich antigen (ST). The Tn antigen contains one residue of GalNAc alpha-O-linked to a serine/threonine residue in the polypeptide chain. Tn antigen can be sialylated to STn by ST6GalNAc-I or can be converted to core 3 structure by C3GnT. Tn antigen is converted to T antigen by T-synthase and further T antigen is converted to ST by ST3Gal-I or core-2 structure by C2GnT [10]. With the known specificities, sialyltransferase FR 180204 ST3Gal-I mediates the sialylation of the T antigen, a key carbohydrate tumor marker. The upregulation of ST3Gal-I has been revealed to be one of the major mechanisms responsible for the sialylation of T antigen. The T antigen is a tumor-associated structure whose sialylated form (the ST antigen) is involved in the altered expression of sialyltransferases and has been usually associated with adverse outcome and poor patient survival in cancer. Cancers of the epithelial origin such as gastric, colorectal, pancreatic, breast, and ovarian often exhibit enhanced expression of Sialyl-Tn (STn) [11, 12]. Furthermore, metastatic colorectal carcinomas show characteristic reduced expression of Tn and T tumor markers with consistent elevated expression of sialylated Tn, T, and Lewis-A and Lewis-X antigens in contrast to primary tumors. It has been widely reported that these antigens can serve as good biomarkers for cancer [13, 14]. ST3Gal-I particularly plays an important role in the sialylation of the T antigen in bladder cancer [12]. In breast carcinoma, the major carrier of T antigen is Mucin 1 (MUC1) [15, 16]. MUC-1 mucin from breast cancer cell lines (MCF-7, BT-20, and T47D) has simpler glycosylation pattern and fewer carbohydrate chains than MUC-1 from normal breast epithelial cells (MMSV1-1, MTSV1-7, and HB-2) with higher ratio of GlcN/GalN. These differences, together or alone, explain the distinct tumor specificity of some T cells and MUC-1 antibodies [17]. Solatycka et al. show that, in breast carcinoma cells, the downregulation of ST3Gal-I is directly correlated with the expression of MUC1 gene and the overexpression of MUC1 affects the carbohydrate-mediated adhesion of breast cancer cells [18]. Hence, during the present study our objective was to develop and characterize monoclonal antibodies against recombinant ST3Gal-I and hence to establish the role of enzyme and confirm its increased expression in cancerous tissues relative to normal cells. The protein was characterized using SDS-PAGE, western blot, and immunohistochemistry of breast cancer FR 180204 tissues. Monoclonal antibodies were generated against the purified ST3Gal-I protein and the antibodies specifically recognized proteins expressed specifically in breast cancer tissues. However, ST3Gal-I and its mAbs need to be clinically validated, at a large platform, for them to be utilized as a.