Membranes were developed using Clearness American ECL substrate (BioRad) or SuperSignal West Femto substrate (Pierce). Immunohistochemistry IHC was conducted on tissue microarrays containing normal and malignant human bladder specimens (Biomax Inc., TMA# BL1002b, BL481b, T121b, and BL244b) as well as pancreatic tissues from mice with transgenic expression of ST6GAL1 (Schultz et?al. ZB55 antibodies have been widely used by investigators, as well as the Human Protein Atlas database, to characterize ST6GAL1 expression. Herein, we used cell and mouse models with controlled expression of ST6GAL1 to compare LN1 and ZB55 with an extensively validated polyclonal antibody to ST6GAL1. We find SC 66 that LN1 and ZB55 do not identify ST6GAL1, and furthermore, these 2 antibodies identify different targets. Additionally, we utilized the well-validated ST6GAL1 antibody to determine that ST6GAL1 is usually overexpressed in bladder malignancy, a finding that contradicts prior studies which employed LN1 to suggest ST6GAL1 is usually downregulated in bladder malignancy. Collectively, our studies underscore the need for careful validation of antibodies purported to recognize ST6GAL1. Keywords: malignancy, CD75, CDw75, sialic acid, ST6GAL1 Introduction Aberrant glycosylation, including increased cell-surface sialylation, is an important biomarker of a tumor cell (Pinho and Reis 2015; Bellis et?al. 2022). One prevalent sialoglycan enriched in tumor cells is the 2C6-linked sialic acid modification added to galactose on SC 66 (neuraminidase, which prefers 2C6-linked sialic acids but can also cleave 2C3 and 2C8 sialic acid linkages. As shown in Fig. 1E, levels of staining by the ZB55 antibody were slightly reduced by both neuraminidases. As well, the 2 2 neuraminidases experienced an equivalent effect SC 66 on ZB55 binding, suggesting that this epitope bound by SC 66 ZB55 does not require the 2C6 sialic acid linkage for acknowledgement. We also examined ZB55 binding to Suit2 EV and OE cells. The overall levels of ZB55 staining were very low for EV and OE cells and no differences were noted in staining intensity (Supplementary Fig. S1B). As mentioned previously, the immunogen used to generate the ZB55 antibody was a peptide derived from FcRIII, which is usually abundant in immune cells but not typically found on epithelial cells. Pretreatment with the neuraminidase slightly reduced staining in both EV and OE cells (Supplementary Fig. S1C). Together, the circulation cytometry data reinforce the immunocytochemistry results (Fig. 1A and B) suggesting that this LN1 and ZB55 antibodies identify different targets, neither of which is usually ST6GAL1. The validated ST6GAL1 antibody, but not ZB55 or LN1, recognizes ST6GAL1 in immunoblotting experiments Whole cell lysates from Suit2 EV and OE cells, as well as CA-46 cells, were immunoblotted using the 3 antibodies. Probing with the R&D ST6GAL1 pAb revealed a single band at ~50 kD in Suit2 OE and CA-46 cells (Fig. 1F), consistent with the expected size of the full-length ST6GAL1 protein (Weinstein et?al. 1987). However, no detectable bands were observed in Suit2 EV lysates. In stark contrast, multiple bands were observed in all 3 cell lines when immunoblotting with the ZB55 and LN1 mAbs. Immunoblotting was also performed with OV4 ovarian malignancy cells, another unusual SC 66 malignancy cell collection that lacks detectable endogenous ST6GAL1 protein expression. As with Suit2 cells, the R&D ST6GAL1 antibody acknowledged a?~50 kD protein in OV4 OE, but not EV, cells, whereas the ZB55 and LN1 antibodies bound to multiple, nonspecific bands (Fig. 1G). Immunoblotting is an important method for antibody screening because the size of the target molecule can be verified (Uhlen et?al. 2016). However, protein denaturation disrupts discontinuous epitopes that may be important for antibody acknowledgement. Immunocytochemistry, a nondenaturing approach, preserves these epitopes. Our immunoblotting results, combined with immunocytochemistry conducted on ST6GAL1 knockout cells (Fig. 1A), provide strong evidence that this R&D pAb specifically recognizes ST6GAL1 and does not cross-react with other proteins. IHC staining with the validated ST6GAL1 antibody, but not LN1 or ZB55, detects ST6GAL1 in tissues from mice with transgenic expression of ST6GAL1 IHC analyses are important for Mouse monoclonal to CD69 delineating cell type-specific expression of a target protein, relative protein levels, and aberrant expression of protein in diseased tissues. We thus conducted IHC staining using tissues from mice with transgenic expression of human ST6GAL1 (genes (and genes (and neuraminidase (Sigma, #10269611001) or 2C3-specific neuraminidase S (BioLabs, #P0743L). Cells were analyzed using an LSRII circulation cytometer and FlowJo V10 was utilized for data analysis. Immunoblotting Cells were lysed in RIPA buffer made up of protease and phosphatase inhibitors (ThermoFisher). BCA assay (Pierce) was utilized for protein quantification. PVDF membranes were blocked in 5% nonfat dry milk for 1?h in Tris-buffered saline with 0.1% Tween 20. Blots were incubated with.