In situ analysis of methylarginine

Aims: To (i) determine whether methylarginine-specific antibodies can be employed for standard immuno- histochemical analysis of paraffin-embedded tissues, (ii) analyse methylarginine expression in normal and neoplastic tissues and (iii) correlate methylarginine expression with that of protein arginine methyltrans- ferase (PRMT1), the predominant cellular arginine methyltransferase. Methods and results: Immunohistochemistry of normal and cancer tissues was performed utilizing three commercial polyclonal antibodies: anti-methylargi- nine-specific antibody (anti-mRG) raised against a methylarginine peptide, Control antibody (anti-RG), a control antiserum raised against a corresponding arginine peptide without any methylated residues and anti-PRMT1. Nuclear and ⁄ or cytoplasmic methylargi- nine expression was detected in all keratinized and non-keratinized epithelia. A preliminary survey of a series of thyroid, pancreatic, colonic and gastric can- cers identified a different pattern of methylarginine expression in comparison with normal tissue. A corre- lation between methylarginine staining and PRMT1 expression was found in all normal and cancer tissues analysed. Conclusion: Methylarginine-specific antibodies are capable of recognizing methylarginine proteins (MeRP) in paraffin-embedded tissues. Methylarginine proteins are expressed widely and show differences in subcellular localization in various organs and neo- plastic conditions. The efficient detection of methyl- proteins by standard immunohistochemistry provides a new tool to investigate the role of methylarginine proteins (MeRP) in biological processes including carcinogenesis.