MUC2 IS THE PROMINENT COLONIC MUCIN EXPRESSED IN ULCERATIVE COLITIS1

Background-It has been shown that MUC2 is the prominent mucin synthesi sed in healthy colon. Aim-To identify the predominant mucins in ulcera tive colitis (UC) and to study their biosynthesis. Methods and Results -Mucin was purified from UC resection specimens. This mucin on sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) presente d as one, high molecular weight, periodic acid/Schiff's reagent (PAS) stainable band. Amino acid composition showed a close resemblance to t hat of MUC2. Immunoprecipitation with a specific anti-MUC2 antiserum c onfirmed that this mucin was MUC2. In addition, on the mRNA level MUC2 was also the most prominent mucin expressed in UC. Polyclonal antiser um was elicited, mainly recognising mucin peptide epitopes of UC and n ormal colonic mucin. Biosynthetic studies with [S-35]amino acids showe d that the MUC2-precursor in UC displayed a molecular mass on SDS-PAGE of approximately 600 kDa. This precursor was converted into a mature MUC2 with anomalous mobility on SDS-PAGE of 550 kDa and was secreted. Only this 550 kDa band could be labelled with [S-35]sulphate and stain ed by PAS. Conclusions-This study shows that in parallel with the muci n expression in healthy controls, MUC2 is the major mucin expressed in UC. Qualitatively, MUC2 biosynthesis seems unchanged in UC.