Golgi apposition promotes the generation of specialized lysosomes in differentiated keratinocytes

Lysosomes, the major degradative compartments of the cell acquire unique properties upon receiving external signals. In the skin, epidermal keratinocytes follow a gradual differentiation process from the basal to the upper skin layers with consequent changes in cellular morphology and intracellular organelles. Previous studies show that keratinocyte differentiation relies on increased lysosome biogenesis. However, the mechanisms of the generation and maintenance of keratinocyte lysosomes remain unknown. Here, we show that dispersed Golgi stacks are distributed to the proximity of lysosomes in differentiated keratinocytes, facilitated by the Golgi tethering protein GRASP65 which associates with the lysosomes. Inhibition of GRASP65 results in the loss of Golgi-lysosome apposition. Further studies exploiting small molecule inhibition and gene modulation reveal a direct role of functional Golgi and its apposition in the generation and, maturation of keratinocyte lysosomes. Selective accumulation of secretory cargo and trans-Golgi enzyme in the lysosome lumen and, reversible dissociation in presence of brefeldin A or Golgicide-A suggests Golgi origin of keratinocyte lysosomes. Taken together, unique Golgi-lysosome apposition and the unconventional properties of keratinocyte lysosomes indicate their possible distinct roles in epidermis homeostasis. Key points Calcium-induced differentiation of human keratinocytes results in the dispersal of functional Golgi stacks and lysosomes Dispersed Golgi stacks remain in close apposition with the lysosomes. Golgi tether GRASP65 surrounds keratinocyte lysosomes GRASP65 depletion disrupts Golgi-lysosome apposition and results in malfunctional lysosomes Lysosomes of differentiated keratinocytes generate from trans-Golgi