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

• Published in: Experimental dermatology Vol. 20; no. 3; pp. 263 - 268
• Main Authors: Aymard, Elodie, Barruche, Vincent, Naves, Thomas, Bordes, Sylvie, Closs, Brigitte, Verdier, Mireille, Ratinaud, Marie-Hélène
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.03.2011; Blackwell; Wiley
• Subjects: Adaptor Proteins, Signal Transducing - metabolism; Adenine - analogs & derivatives; Adenine - pharmacology; Adenylate Kinase - metabolism; apoptosis; Apoptosis Regulatory Proteins - metabolism; Autophagy - drug effects; Autophagy - physiology; Autophagy-Related Protein 12; Autophagy-Related Protein 5; Autophagy-Related Protein 8 Family; bcl-X Protein - metabolism; Beclin-1; Biological and medical sciences; Calcium - pharmacology; Cathepsin B - metabolism; Cell Cycle - drug effects; Cell Cycle - physiology; Cell Differentiation - drug effects; Cell Differentiation - physiology; Cell Line, Transformed; Culture Media, Serum-Free - pharmacology; Dermatology; HaCaT line; Human health and pathology; Humans; Integrin beta1 - metabolism; Keratin-10 - metabolism; Keratinocytes - cytology; Keratinocytes - drug effects; Keratinocytes - metabolism; Life Sciences; Medical sciences; Membrane Proteins - metabolism; Microfilament Proteins - metabolism; Microtubule-Associated Proteins - metabolism; Phosphorylation - drug effects; Protein Precursors - metabolism; Sirtuin 1 - metabolism; Small Ubiquitin-Related Modifier Proteins - metabolism; Stress, Physiological - physiology; Transcription Factors - metabolism; Tumor Suppressor Proteins - metabolism; Human; Keratinocyte; HaCaT line; Dermatology; Apoptosis
• ISSN: 0906-6705; 1600-0625; 1600-0625
• DOI: 10.1111/j.1600-0625.2010.01157.x

:  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 G1 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‐XL 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.