Compensatory endocytosis in bladder umbrella cells occurs through an integrin‐regulated and RhoA‐ and dynamin‐dependent pathway

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Abstract
Compensatory endocytosis (CE) ensures recycling of membrane components and maintenance of plasma membrane size; however, the mechanisms, regulation, and physiological functions of clathrin‐independent modes of CE are poorly understood. CE was studied in umbrella cells, which undergo regulated exocytosis of subapical discoidal/fusiform vesicles (DFV) during bladder filling, and may then replenish the pool of DFV by internalizing apical membrane during voiding. We found that voiding‐stimulated CE, which depended on β1 integrin‐associated signalling pathways, occurred by a dynamin‐, actin‐, and RhoA‐regulated mechanism and was independent of caveolins, clathrin, and flotillin. Internalized apical membrane and fluid were initially found in ZO‐1‐positive vesicles, which were distinct from DFV, classical early endosomes, or the Golgi, and subsequently in lysosomes. We conclude that clathrin‐independent CE in umbrella cells functions to recover membrane during voiding, is integrin regulated, occurs by a RhoA‐ and dynamin‐dependent pathway, and terminates in degradation and not recapture of membrane in DFV.

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