Zymogen granule (ZG) formation in acinar cells involves zymogen-cargo sorting from trans-Golgi into immature secretory granules (ISGs). ISG maturation progresses by removal of lysosomal membrane and select-content proteins which enter endosomal intermediates prior to their apical exocytosis. Constitutive and stimulated secretion through this mechanism is termed the constitutive-like (CLP) and minor-regulated (MRP) pathways, respectfully. However, the molecular components that control membrane trafficking within these endosomal compartments are unknown. We show that tumor protein D52 is highly expressed in endosomal compartments following pancreatic acinar stimulation and regulates apical exocytosis of an apically directed endolysosomal compartment. Secretion from the endolysosomal compartment was detected by cell-surface labeling of lysosome associated membrane protein LAMP1, which is absent from ZGs, and had incomplete overlap with surface labeling of synaptotagmin, a marker of ZG exocytosis. Although culturing (16-18 h) of isolated acinar cells is accompanied by a loss of secretory responsiveness, levels of SNARE proteins necessary for ZG exocytosis were preserved. However, levels of endolysosomal proteins D52, EEA1, Rab5 and LAMP1 markedly decreased. When D52 levels were restored by adenoviral delivery, the levels of these regulatory proteins and secretion of both LAMP1 (endolysosomal) and amylase was strongly enhanced. These secretory effects were absent in alanine and aspartate substitutions of serine 136, the major D52 phosphorylation site, and were inhibited by brefeldin A, which does not directly affect the ZG compartment. Results indicate D52 directly regulates apical endolysosomal secretion and are consistent with previous studies suggesting this pathway indirectly regulates ZG secretion of digestive enzymes.