Induction of endoplasmic reticulum stress by sonoporation: linkage to mitochondria-mediated apoptosis initiation.
The use of cavitational means to create transient membrane pores on living cells (i.e., sonoporation) may potentially induce a broad range of downstream bio-effects that disrupt the functioning of various organelles. Here we observed that on HL-60 leukemia cells, sonoporation may induce endoplasmic reticulum (ER) stress on a time-lapse basis and, in turn, signal the mitochondria to commit a cell toward apoptosis. Our observations were derived from in vitro ultrasound exposure experiments performed on HL-60 cells in the presence of lipid-shelled microbubbles (1:1 cell-to-bubble ratio; 1-MHz frequency; 0.45-MPa in situ peak negative pressure; 100-cycle pulse length; 1-kHz pulse repetition frequency; 60-s exposure period). Using flow cytometry, we found that sonoporated cells exhibited a progressive loss of functional ER mass over a 6-h period. Also, post-exposure Western blot assays (between 0 and 24 h) revealed various indications of post-sonoporation ER stress: (i) upregulation of ER-resident enzymes responsible for catalyzing protein folding; (ii) activation of trans-ER-membrane stress sensors; (iii) increased expression of ER-induced regulatory proteins that mediate pro-apoptotic signals to the mitochondria. These results corresponded to flow cytometry observations that depicted a progressive depolarization of a sonoporated cell's mitochondrial outer membrane potential. They were also consistent with another Western blot assay that found, in sonoporated cells, a time-lapse increase of caspase-9 (a mitochondria-activated apoptosis initiator protein). Taken together, our findings indicate that sonoporation may upset ER homeostasis, and this may ultimately result in initiation of apoptosis.
Medical Engineering Program, University of Hong Kong, Pokfulam, Hong Kong.
Wenjing
W
Zhong
Xian
X
Chen
Pingping
P
Jiang
Jennifer M F
JM
Wan
Peng
P
Qin
Alfred C H
AC
Yu
D017209:Apoptosis / Q000528:radiation effects; D018274:Electroporation / Q000379:methods*; D004721:Endoplasmic Reticulum / Q000502:physiology* / Q000528:radiation effects*; D018922:HL-60 Cells; D019220:High-Energy Shock Waves; D006801:Humans; D008928:Mitochondria / Q000502:physiology* / Q000528:radiation effects*; D013010:Sonication / Q000379:methods*; D013312:Stress, Physiological / Q000502:physiology / Q000528:radiation effects
Apoptosis; Endoplasmic reticulum; Mitochondria; Signaling pathway; Sonoporation; Stress response