Carcinogenesis Advance Access originally published online on September 26, 2009
Carcinogenesis 2009 30(11):1880-1888; doi:10.1093/carcin/bgp235
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Rac1/MKK7/JNK pathway signals upregulation of Atg5 and subsequent autophagic cell death in response to oncogenic Ras
1 Laboratory of Molecular Biochemistry, Department of Chemistry, Hanyang University, 17 Haengdang-Dong, Seongdong-Ku, Seoul 133-791, Korea
2 Department of Microbiological Engineering, KonKuk University, Seoul 143-701, Korea
3 Division of Radiation Biology
4 Division of Radiation Cancer Biology, Korea Institute of Radiological and Medical Sciences, Seoul 139-706, Korea
5 Research Institute of Natural Sciences, Hanyang University, 17 Haengdang-Dong, Seongdong-Ku, Seoul 133-791, Korea
* To whom correspondence should be addressed. Tel: +82 2 2220 2557; Fax: +82 2 2299 0762; Email: sj0420{at}hanyang.ac.kr
Correspondence may also be addressed to Min-Jung Kim. Tel: +82 2 2220 4554; Fax: +82 2 2299 0762; Email: kimmj74{at}hanyang.ac.kr
To prevent the development of malignancies, mammalian cells activate disposal programs, such as programmed cell death, in response to deregulated oncogene expression. However, the molecular basis for regulation of cellular disposal machinery in response to activated oncogenes is unclear at present. In this study, we show that upregulation of the autophagy-related protein, Atg5, is critically required for the oncogenic H-ras-induced autophagic cell death and that Rac1/mitogen-activated kinase kinase (MKK) 7/c-Jun N-terminal kinase (JNK) signals upregulation of Atg5. Overexpression of H-rasV12 induced marked autophagic vacuole formation and cell death in normal fibroblasts, which remained unaffected by a caspase inhibitor. Pretreatment with Bafilomycin A1, an autophagy inhibitor, completely attenuated H-rasV12-induced cell death as well as autophagic vacuole formation. Selective production of Atg5 was observed in cells overexpressing H-rasV12, and small interfering RNA (siRNA) targeting of Atg5 clearly inhibited autophagic cell death. Interestingly, inhibition of JNK or c-Jun by specific siRNA suppressed Atg5 upregulation and autophagic cell death. Moreover, inhibition of MKK7, but not MKK4, effectively attenuated H-rasV12-induced JNK activation. In addition, ectopic expression of RacN17 or Rac1-siRNA effectively inhibited MKK7–JNK activation, Atg5 upregulation and autophagic cell death. These data support the notion that upregulation of Atg5 is required for the oncogenic H-ras-induced autophagic cell death in normal fibroblasts and that activation of Rac1/MKK7/JNK-signaling pathway leads to upregulation of Atg5 in response to oncogenic H-ras. Our findings suggest that in cells acquiring deregulated oncogene expression, oncogenic stress triggers autophagic cell death, which protects cells against malignant progression.
Abbreviations: ERK, extracellular signal-regulated kinase; GFP, green fluorescent protien; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated protein kinase; MKK, mitogen-activated kinase kinase; siRNA, small interfering RNA
Received May 14, 2009; revised August 23, 2009; accepted September 19, 2009.