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Mechanisms of H‐Ras‐induced autophagic cell death in human glioblastoma
Author(s) -
Kaul Aparna,
Overmeyer Jean H.,
Zeng Xuehuo,
Maltese William A.
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.5.a981-c
Subject(s) - autophagy , microbiology and biotechnology , vacuole , biology , anti apoptotic ras signalling cascade , programmed cell death , pi3k/akt/mtor pathway , gene silencing , kinase , phosphatidylinositol , signal transduction , staurosporine , protein kinase a , apoptosis , cancer research , mapk/erk pathway , gene , cytoplasm , genetics
Activating mutations in H‐Ras (e.g., G12 →V) render the protein oncogenic in many types of cells. However, in glioblastoma cells expression of H‐Ras(G12V) triggers caspase‐independent cell death that commences with accumulation of vacuoles resembling large autophagosomes and autolysosomes. The cells expressing H‐Ras(G12V) lose the ability to form colonies in soft agar and exhibit a marked increase in production of LC3‐II, a phosphatidylethanolamine‐conjugated protein associated with autophagosome membranes. Therefore, we tested the hypothesis that signals generated by H‐Ras in glioblastoma cells may hyper‐activate the autophagic machinery that typically responds to nutrient deprivation. The results of immunoblot studies indicate that H‐Ras(G12V) does not decrease the activity of the nutrient‐sensing kinase, mTOR. Moreover, siRNA gene silencing experiments indicate that accumulation of vacuoles does not require the mammalian autophagy protein, Beclin‐1. Studies utilizing Ras‐effector domain mutants and an inhibitor of MEK suggest that activation of the Raf‐MEK‐ERK1/2 signaling cascade is not responsible for induction of non‐apoptotic cell death in glioblastoma. Likewise, preliminary studies indicate that vacuolization of the cells probably is not attributable to activation of phosphatidylinositol 3′‐kinase (PI3‐kinase). Taken together, the results indicate that some of the recently identified H‐Ras signaling pathways may trigger autophagic cell death in glioblastoma via a novel mechanism distinct from classical nutrient‐dependent macroautophagy. Supported by a grant from the NIH (R01CA34569) to W.A.M.