Keratinocyte differentiation promotes ER stress-dependent lysosome biogenesis

Sarmistha Mahanty,Mruthyunjaya Mathapathi Swamy,Shruthi Shirur Dakappa,Amitabha Majumdar,Saloni Patel,Rezwan Shariff,Subba Rao Gangi Setty

doi:10.1038/s41419-019-1478-4

Sarmistha Mahanty, Mruthyunjaya Mathapathi Swamy + Show 5 more

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https://doi.org/10.1038/s41419-019-1478-4

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Abstract

Keratinocytes maintain epidermal integrity through cellular differentiation. This process enhances intraorganelle digestion in keratinocytes to sustain nutritional and calcium-ionic stresses observed in upper skin layers. However, the molecular mechanisms governing keratinocyte differentiation and concomitant increase in lysosomal function is poorly understood. Here, by using primary neonatal human epidermal keratinocytes, we identified the molecular link between signaling pathways and cellular differentiation/lysosome biogenesis. Incubation of keratinocytes with CaCl2 induces differentiation with increased cell size and early differentiation markers. Further, differentiated keratinocytes display enhanced lysosome biogenesis generated through ATF6-dependent ER stress signaling, but independent of mTOR-MiT/TFE pathway. In contrast, chemical inhibition of mTORC1 accelerates calcium-induced keratinocyte differentiation, suggesting that activation of autophagy promotes the differentiation process. Moreover, differentiation of keratinocytes results in lysosome dispersion and Golgi fragmentation, and the peripheral lysosomes showed colocalization with Golgi-tethering proteins, suggesting that these organelles possibly derived from Golgi. In line, inhibition of Golgi function, but not the depletion of Golgi-tethers or altered lysosomal acidity, abolishes keratinocyte differentiation and lysosome biogenesis. Thus, ER stress regulates lysosome biogenesis and keratinocyte differentiation to maintain epidermal homeostasis.

Highlights

Human epidermis is majorly composed of proliferative and differentiated keratinocytes organized into four distinct layers[1,2]
ER stress regulates keratinocyte differentiation and lysosome biogenesis To understand the mechanism of calcium-induced keratinocyte differentiation and its molecular link with lysosome biogenesis, we evaluated the role of the key components of calcium signaling and lysosome/Golgi biogenesis by using chemical inhibitors/modulators (Table 1)
Extracellular high calcium has been shown to play a key role in inducing keratinocyte differentiation[2], but its role in

Summary

Introduction

Human epidermis is majorly composed of proliferative and differentiated keratinocytes organized into four distinct layers[1,2]. These sublayers are characterized by specific gene expression and predicted to be formed due to the pre-existing calcium gradient in the layers[3,4,5,6]. Proliferative keratinocytes of stratum basale constantly undergo differentiation towards the upper layers and form stratum corneum, and maintains epidermal homeostasis. Terminally differentiated keratinocytes lose their intracellular organelles including nuclei by increasing macroautophagy[7,8]. The mechanism of calcium influence on cellular differentiation and its link to organelle homeostasis is poorly understood.

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