HAMLET (human alpha-lactalbumin made lethal to tumor cells) triggers autophagic tumor cell death.
HAMLET, a complex of partially unfolded alpha-lactalbumin and oleic acid, kills a wide range of tumor cells. Here we propose that HAMLET causes macroautophagy in tumor cells and that this contributes to their death. Cell death was accompanied by mitochondrial damage and a reduction in the level of active mTOR and HAMLET triggered extensive cytoplasmic vacuolization and the formation of double-membrane-enclosed vesicles typical of macroautophagy. In addition, HAMLET caused a change from uniform (LC3-I) to granular (LC3-II) staining in LC3-GFP-transfected cells reflecting LC3 translocation during macroautophagy, and this was blocked by the macroautophagy inhibitor 3-methyladenine. HAMLET also caused accumulation of LC3-II detected by Western blot when lysosomal degradation was inhibited suggesting that HAMLET caused an increase in autophagic flux. To determine if macroautophagy contributed to cell death, we used RNA interference against Beclin-1 and Atg5. Suppression of Beclin-1 and Atg5 improved the survival of HAMLET-treated tumor cells and inhibited the increase in granular LC3-GFP staining. The results show that HAMLET triggers macroautophagy in tumor cells and suggest that macroautophagy contributes to HAMLET-induced tumor cell death.
Aits
Sonja
S
Institute of Laboratory Medicine, Section of Microbiology, Immunology and Glycobiology, Lund University, Lund, Sweden.
Gustafsson
Lotta
L
Hallgren
Oskar
O
Brest
Patrick
P
Gustafsson
Mattias
M
Trulsson
Maria
M
Mossberg
Ann-Kristin
AK
Simon
Hans-Uwe
HU
Mograbi
Baharia
B
Svanborg
Catharina
C
D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology; D001343:Autophagy / Q000187:drug effects*; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D045744:Cell Line, Tumor; D006801:Humans; D007768:Lactalbumin / Q000494:pharmacology*; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D008928:Mitochondria / Q000187:drug effects; D009829:Oleic Acids / Q000494:pharmacology*; D011494:Protein Kinases / Q000032:analysis; D012333:RNA, Messenger / Q000032:analysis; D058570:TOR Serine-Threonine Kinases
C502778:ATG5 protein, human; D051017:Apoptosis Regulatory Proteins; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; C506422:HAMLET complex, human; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D009829:Oleic Acids; D012333:RNA, Messenger; D007768:Lactalbumin; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases