Autophagy in human keratinocytes: an early step of the differentiation?

Abstract

Studies have established that autophagy constitutes an efficient process to recycle cellular components and certain proteins. The phenomenon was demonstrated primarily in response to nutrient starvation, and there are increasing evidences that it is implied in differentiation. Keratinocyte differentiation was going along an activation of lysosomal enzymes and organelle clearance, and terminal steps are sometimes described as a specialized form of cell death leading to corneocytes. We examined whether initiation of the process in human keratinocyte HaCaT involves autophagy. The KSFM™ culture medium was substituted by M199, which contains a low glucose concentration but a high calcium level (known to induce differentiation). Metabolic stress reduced enhanced cell number in G(1) phase, without apoptotic features (ΔΨmt and membrane integrity are unchanged). Morphological changes were associated with a lower integrin ß1 expression and modifications of protein levels involved in keratinocyte differentiation (involucrin, keratin K10 and ΔNp63α). Whereas autophagic signalling was supported by SIRT1 and pAMPK (T172) increase according to time kinetic, which led to the disappearance of mTOR phosphorylated on S2448 residue. The significant Bcl-X(L) level reduction with stress promoted autophagy, by the release of Beclin-1, whereas ATG5-ATG12 and LC3-II that are involved in autophagosome formation were enhanced significantly. Then, the level of lysosomal protein cathepsin B rose to execute autophagy. Kinetic studies established that autophagy would constitute an early signalling process required for keratinocyte commitment in differentiation pathway.

Novel Phosphoinositide 3-Kinase/mTOR Dual Inhibitor, NVP-BGT226, Displays Potent Growth-Inhibitory Activity against Human Head and Neck Cancer Cells In Vitro and In Vivo

“…In fact, recent studies have focused on cell death that is unrelated to apoptosis or caspase activation. One route is through lysosomal dysfunction with the activation of cathepsin (43), and indeed, cathepsin is often associated with the autophagic process (44,45). Our experimental results show that the activation of cathepsin B/L in FaDu is significantly elicited in the presence of BGT226 (Supplementary Fig.…”

MCP-1-Induced Protein Promotes Endothelial-Like and Angiogenic Properties in Human Bone Marrow Monocytic Cells

“…Differentiation also involves disappearance of one set of proteins by a self-digestion process such as autophagy, which has been demonstrated to be involved in differentiation in several contexts (Aymard et al, 2011;Salemi et al, 2012). The results presented here demonstrate that enhanced expression of MCPIP induced ER stress and autophagy during the process of MCPIP-mediated EC differentiation.…”

iASPP is a novel autophagy inhibitor in keratinocytes

“…Several reports have recently described the autophagy process occurring in monolayer cultures of keratinocytes (Aymard et al, 2011;Chatterjea et al, 2011;Deruy et al, 2010;Gosselin et al, 2009;Lee et al, 2011;Silva et al, 2010;Tong et al, 2012;Wang and Levine, 2011;Zhao et al, 2013;Zhou and Münger, 2009). Autophagy is a highly conserved proteolytic mechanism that maintains the homeostasis of the cell by degrading organelles and cytoplasmic material.…”