Cytoplasmic signaling involved in sonoporation-induced apoptosis andmitosis repression of myeloid leukemia cells

Abstract

Sonoporation is known to be a transient phenomenon that may disrupt thehomeostasis of living cells. In this work, we showed that sonoporation may beartime-lapse impact on cellular viability through up-regulation of cytoplasmicsignaling proteins related to apoptosis and cell-cycle arrest. Our experimentswere done on HL-60 leukemia cells (10 6 cells/ml), and sonoporationwas induced via the use of 1% v/v microbubbles and 1-min. pulsed ultrasoundexposure (0.5MPa peak negative pressure, 1MHz center frequency, 10% duty cycle,1 kHz pulse repetition frequency). The transient nature of sonoporation in thesecells was confirmed by performing scanning electron microscopy on selected cellsamples that were fixed respectively after a few seconds into the ultrasoundexposure and one minute after the end of exposure. Cytoplasmic signaling changesof these cells were studied at four post-sonoporation time points (4h, 8h, 12h,24h) using western blot analysis. Five signaling proteins related to apoptosisand mitosis were analyzed in this work: 1) PARP (for DNA repair); 2)cleaved-PARP (fragments due to cleavage by pro-apoptotic caspase proteins); 3)Bcl-2 (inhibitor for mitochrondrial release of pro-apoptotic molecules); 4) Bax(complement of Bcl-2); 5) Cdc-2 (regulator for cell mitosis). Three key resultswere found from the cytoplasmic signaling analysis. First, PARP levels werereduced over the monitoring period whilst cleaved-PARP had increased inexpression, and in turn they indicate that the cells' anti-apoptotic responseswere dampened following sonoporation and pro-apoptotic caspase proteins werelikely activated. Second, drop in Bcl-2 and rise in Bax were observed, and thesesuggest that the mitochondrion was involved in apoptotic signal transductioninside sonoporated cells. Third, Cdc-2 was seen to decrease, implying thatmitosis was repressed in sonoporated cells. © 2010 IEEE.published_or_final_versionThe 2010 IEEE International Ultrasonics Symposium, San Diego, CA., 11-14 October 2010. In Proceedings of IEEE IUS, 2010, p. 1771-177