Combined regulation of mTORC1 and lysosomal acidification by GSK-3 suppresses autophagy and contributes to cancer cell growth.

Abstract

There is controversy over the role of glycogen synthase kinase-3 (GSK-3) in cancer progression. Recent work has implicated GSK-3 in the regulation of mammalian target of rapamycin (mTOR), a known player in malignant transformation. Autophagy, a self-degradation pathway, is inhibited by mTOR and is tightly associated with cell survival and tumor growth. Here we show that GSK-3 suppresses autophagy via mTOR complex-1 (mTORC1) and lysosomal regulation. We show that overexpression of GSK-3 isoforms (GSK-3α and GSK-3β) activated mTORC1 and suppressed autophagy in MCF-7 human breast cancer cells as indicated by reduced beclin-1 levels and upregulation of sequestosome 1 (p62/SQSTM1). Further, overexpression of GSK-3 increased the number of autophagosomes and inhibited autophagic flux. This activity was directly related to reduced lysosomal acidification triggered by GSK-3 (in which GSK-3β has a stronger impact). We found that lysosomal acidification is reduced in MCF-7 cells that also exhibit increased levels of autophagosomes and p62/SQSTM1 and increased activity of mTORC1. Subsequently, treating cells with GSK-3 inhibitors restored lysosomal acidification, enhanced autophagic flux and inhibited mTORC1. Furthermore, GSK-3 inhibitors inhibited cell proliferation. We provide evidence that GSK3-mediated mTORC1 activity and GSK-3-mediated lysosomal acidification occur via distinct pathways, yet both mTORC1 and lysosomes control cell growth. Finally, we show that GSK-3-reduced lysosomal acidification inhibits endocytic clearance as demonstrated by reduced endocytic degradation of the epidermal growth factor receptor. Taken together, our study places GSK-3 as a key regulator coordinating cellular homeostasis. GSK-3 inhibitors may be useful in targeting mTORC1 and lysosomal acidification for cancer therapy.

• Authors: I Azoulay-Alfaguter, R Elya, L Avrahami, A Katz, H Eldar-Finkelman
• Journal: Oncogene (Oncogene) Vol. 34 Issue 35 Pg. 4613-23 (Aug 27 2015) ISSN: 1476-5594 [Electronic] England
• PMID: 25500539 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Multiprotein Complexes
• Mechanistic Target of Rapamycin Complex 1
• TOR Serine-Threonine Kinases
• Glycogen Synthase Kinase 3

Topics

• Autophagy
• Cell Proliferation
• Endocytosis
• Glycogen Synthase Kinase 3 (physiology)
• Humans
• Hydrogen-Ion Concentration
• Lysosomes (enzymology)
• MCF-7 Cells
• Mechanistic Target of Rapamycin Complex 1
• Multiprotein Complexes (physiology)
• Phagosomes (metabolism)
• TOR Serine-Threonine Kinases (physiology)