MYO5B deficiency is associated with altered MUC13 localization and DMBT1 accumulation in intestinal epithelial cells.

Myosin 5b (MYO5B) is a motor protein that plays an essential role in trafficking proteins to the apical membrane. Recent studies have demonstrated that MYO5B traffics ion transporters, like NHE3, DRA, and SGLT1, water channels, like AQP7, and efflux transporters, like P-glycoprotein. However, the role of MYO5B in trafficking glycoproteins involved in mucosal defense remains unclear. Here, we investigate whether MYO5B is required for the apical localization of mucin 13 (MUC13) and deleted in malignant brain tumors 1 (DMBT1), two glycoproteins critical for epithelial protection and wound healing. To address the requirement of MYO5B in glycoprotein trafficking, we immunostained the small intestine and colon of neonatal germline and adult inducible intestine-specific MYO5B knockout (KO) mice and examined MUC13 and DMBT1 localization. Organoids derived from germline and inducible KO mice were analyzed to confirm findings in an epithelial-only system. In addition, staining was performed on human organoids expressing MYO5B-tail green fluorescent protein (GFP). MYO5B loss in vivo resulted in the intracellular accumulation of MUC13 and DMBT1, reducing their colocalization with the apical marker γ-actin in both models. MUC13 colocalized with the lysosomal marker lysosomal-associated membrane protein 1 (LAMP1) in adult mice after MYO5B loss, indicating that a portion of cytoplasmic MUC13 undergoes lysosomal degradation. Mislocalization of MUC13 was observed in vitro in intestinal MYO5B-deficient organoids. MYO5B-tail GFP was associated with MUC13 in human intestinal organoids. MYO5B is required for the apical delivery of MUC13 and DMBT1 in the intestinal epithelium. Disrupting this pathway may contribute to mucosal dysfunction in MYO5B-related diseases, highlighting potential therapeutic targets for restoring epithelial barrier integrity.NEW & NOTEWORTHY This work identifies MYO5B as an important regulator of the apical localization of the mucosal defense glycoprotein MUC13. Our findings suggest a link between epithelial trafficking machinery and glycocalyx organization, demonstrating that MYO5B deficiency is associated with altered localization of these proteins and increased lysosomal accumulation of MUC13. These observations provide additional insight into epithelial dysfunction in MYO5B-associated enteropathies and may have broader relevance to inflammatory bowel disease.