RNA disruption is associated with response to multiple classes of chemotherapy drugs in tumor cell lines

Narendrula, Rashmi; Mispel-Beyer, Kyle; Guo, Baoqing; Parissenti, Amadeo M.; Pritzker, Laura B.; Pritzker, Ken; Masilamani, Twinkle; Wang, Xiaohui; Lannér, Carita

The degradation of rRNA by cytotoxic stressors has been shown to correlate with the induction of apoptosis in several cell systems [11, 12, 16, 17, 24, 25, 29] . In the current study, the chemotherapy drug docetaxel appeared to induce apoptosis in A2780 cells, as evidenced by elevated annexin V binding (peaking at 72 h; Fig. 6a ), increased caspase-3 activity (peaking at 24 h; Fig. 8a ), and a dramatic rise in the amount of apoptotic bodies with a sub-G 1 DNA content (peaking at 72 h; Fig. 6b ). RNA disruption was also induced by docetaxel in A2780 cells and was highest at 72 h in this study (Fig. 1 ). This suggested a temporal correlation between the induction of apoptosis and RNA disruption. The association of RNA disruption with apoptosis is also suggested by our findings that the cell permeable caspase inhibitor Q-DEVD-Oph was able to partially suppress both caspase-3 activity and docetaxel-induced RNA disruption (Fig. 8b, c, and d) . This is consistent with previous findings that apoptosis associated rRNA degradation is dependent upon caspase activation [24, [30] [31] [32] [33] [34] . However, apoptosis can occur without RNA disruption [35] and rRNA cleavage has been observed in the absence of caspase-and BCL-2 dependent apoptosis [16, 17, 25, 36] , suggesting that these two processes can occur independently of each other. Moreover, there is increasing evidence that caspases (such as caspase-3 and caspase-7) may play a role in cell cycle progression independent of their role in promoting cell death [37, 38] . Similarly, the role of caspases in RNA disruption may be unrelated to their role in apoptosis. Our results also show that docetaxel treatment of A2780 cells did not promote DNA laddering (Fig. 6c) , a common phenomenon associated with apoptosis in many cell types. However, lack of DNA degradation during apoptosis has been reported in a number of studies [35, [39] [40] [41] . Our findings suggest that docetaxel-induced apoptosis in A2780 cells lacks a mechanism for activating DNA fragmentation, while the RNA fragmentation mechanism is not blocked. It is also worth noting that additional studies in our laboratory indicated that apoptotic biomarkers (cleaved caspase-3 and PARP cleavage) wane considerably by 72 h (Additional file 6), while RNA disruption products persist (Figs. 1, 2, and 3) . RNA disruption may thus be a preferable biomarker for identifying cells/tissues/patients responding to chemotherapy [18, 20] .