HCV core sensitized ATRA-induced cell death. (A) Production levels of the core in each clone of MCF-7 cells stably transfected with pLXSH-core (MCF-7-core 6 and -core 21) or the empty vector pLXSH (MCF-7-vec) were analyzed by immunoblot analysis with an anti-core (right, upper panel) and an anti-α-tubulin (right, lower panel) antibody as an internal control. MCF-7-core 6, MCF-7-core 21, and MCF-7-vec cells (5 × 104 each) were incubated in the absence (no treatment) or presence (ATRA) of 1 μM ATRA for 96 h. Living and dead cells were quantitated by staining with trypan blue. The average percentage of cell death from three independent experiments is presented. Open (bars 1 and 4), solid (bars 2 and 5), and hatched (bars 3 and 6) bars, MCF-7-vec, -core 6, and -core 21, respectively. (B) MCF-7 cells (5 × 104) transfected with 2.5 μg of pMACS-Kk and each expression plasmid given below were treated with (solid bars) or without (open bars) 1 μM ATRA for 96 h after the concentration of transfected cells by using the MACSelect system (see Materials and Methods). For bars 11 and 12, 50 μM monodansylcadaverine (MDC) was added simultaneously with ATRA. The percentage of cell death was estimated as described for panel A. Bars 1 and 2, empty vector; bars 3, 4, 11, and 12, pCMV-core (3 μg); bars 5 and 6, pCMV-core (6 μg); bars 7 and 8, pCMV-core (3 μg) and pCMV-Sp110b(389-453) (CBR fragment; 4.5 μg); bars 9 and 10, pCMV-core(6162M) (3 μg). (C) Enhancement of ATRA-induced tTGase expression by the core. MCF-7 cells (2 × 105) transfected with pMACS-Kk and each expression plasmid given below were treated for 48 h with (lanes 4 to 6) or without (lanes 1 to 3) 1 μM ATRA after cell concentration as described for panel B. Following the extraction of total RNA from these cells, mRNA levels of tTGase (upper panel) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as an internal control (lower panel) were semiquantified by RT-PCR as described in Materials and Methods. RTase(−), experimental control treated like other samples, but without reverse transcriptase. Lanes: 1 and 4, empty vector; 2 and 5, pCMV-core; 3 and 6, pCMV-core and pCMV-Sp110b(389-453) (CBR fragment).