Mucin 21 confers resistance to apoptosis in an O-glycosylation-dependent manner

Abstract

Highly glycosylated mucins protect epithelial surfaces from external insults and are related to malignant behaviors of carcinoma cells. However, the importance of carbohydrate chains on mucins in the process of cellular protection is not fully understood. Here, we investigated the effect of human mucin-21 (MUC21) expression on the susceptibility to apoptosis. MUC21 transfection into HEK293 cells decreased the number of apoptotic cells in culture media containing etoposide or after ultraviolet light irradiation. We used Chinese hamster ovary (CHO) cell variants to investigate the importance of MUC21 glycosylation in the resistance to apoptosis. When MUC21 was expressed in CHO-K1 cells, it was glycosylated with sialyl T-antigen and the cells showed resistance to etoposide-induced apoptosis. MUC21 transfection into Lec2 cells, a variant of CHO cells lacking sialylation of glycans, revealed that the presence of nonsialylated T-antigen also renders cells resistant to etoposide-induced apoptosis. MUC21 was transfected into ldlD cells and the glycosylation was manipulated by supplementation to the medium. Nonsupplemented cells and cells supplemented with N-acetylgalactosamine showed no resistance to etoposide-induced apoptosis. In contrast, these cells supplemented with N-acetylgalactosamine plus galactose expressed sialyl T-antigen and exhibited resistance to etoposide-induced apoptosis. Finally, galectin-3 knockdown in MUC21 transfectants of HEK293 cells did not significantly affect MUC21-dependent induction of apoptosis resistance. The results suggest that T-antigen with or without sialic acid is essential to the antiapoptotic effect of MUC21.

Unique Glycoform-Dependent Monoclonal Antibodies for Mouse Mucin 21

“…Furthermore, by knocking down β-galactoside α2-6-sialyltransferase ST6Gal-1, which catalyzes the addition of sialic acid to galactose, ovarian tumor cells gained cisplatin resistance [ 30 ]. Together with a recent study showing that the overexpression of human T-MUC21 and sialyl T-MUC21 confers anti-apoptotic properties to cells, whereas non-glycosylated MUC21 and Tn-MUC21 do not [ 11 ], these findings underscore the importance of glycoforms in the regulation of mucin function. The 1A4-1 and 18A11 mAbs will potentially be useful tools to elucidate this structure–function relationship in Muc21.…”

“…Recent studies have shown that MUC21 acts a negative marker for epithelioid mesothelioma [ 9 ] and that MUC21 proteins with a specific glycosylation status may be involved in the progression of EGFR-mutated lung adenocarcinomas [ 10 ]. Finally, we reported that the expression of MUC21 confers resistance to apoptosis in an O -glycosylation-dependent manner, underscoring the glycoform-dependent functions of mucins [ 11 ]. Although monoclonal antibodies specific to several glycoforms of human MUC21 have been previously established, antibodies for mouse Muc21 have not been previously obtained.…”

Tamoxifen-resistant breast cancer cells exhibit reactivity with Wisteria floribunda agglutinin

“…One important aspect is that glycosylation is known to modulate the function of molecules involved in apoptosis [ 20 ]. We recently reported that Mucin 21 confers resistance to apoptosis in an O-glycosylation-dependent manner [ 21 ]. Another aspect is that the function of drug transporters is glycosylation-dependent [ 22 – 24 ], with studies showing that different glycans influence the sensitivity to different drugs through a variety of mechanisms.…”

MUC21: a new target for tumor treatment

“…The latest research indicates that specific glycosylated MUC21 may be involved in the development of lung adenocarcinoma with EGFR mutations ( 22 ). In addition, the over-expression of human T-MUC21 and sialylated T-MUC21 confers cells with anti-apoptotic characteristics, whereas unglycosylated MUC21 and Tn-MUC21 do not possess this characteristic ( 37 , 38 ). These findings underscore the importance of glycosylation in regulating the function of mucins.…”

“…Tian et al. discovered that the anti-apoptotic capability of CHO cells expressing O-glycosylated MUC21 increased, with the expression of T-MUC21 and sialylated T-MUC21 in these cells imparting an anti-apoptotic characteristic ( 37 ). Conversely, the expression of unmodified MUC21 or Tn-MUC21 did not endow these cells with an anti-apoptotic trait ( 37 ).…”