Ubiquinone derivatives modulate the mammalian mitochondrial Permeability Transition Pore (PTP). Yeast mitochondria harbor a similar structure: the respiration- and ATP-induced Saccharomyces cerevisiae Mitochondrial Unselective Channel ( Sc MUC). Here we show that decylubiquinone, a well-characterized inhibitor of the PTP, suppresses Sc MUC opening in diverse strains and independently of respiratory chain modulation or redox-state. We also found that naturally occurring derivatives such as hexaprenyl and decaprenyl ubiquinones lacked effects on the Sc MUC. The PTP-inactive ubiquinone 5 (Ub5) promoted the Sc MUC-independent activation of the respiratory chain in most strains tested. In an industrial strain however, Ub5 blocked the protection elicited by dUb. The results indicate the presence of a ubiquinone-binding site in the Sc MUC.

Persistent infections with some types of human papillomavirus (HPV) constitute the major etiological factor for cervical cancer development. Nanog, a stem cell transcription factor has been shown to increase during cancer progression. We wanted to determine whether Nanog could modulate transcription of E6 and E7 oncogenes. We used luciferase reporters under the regulation of the long control region (LCR) of HPV types 16 and 18 (HPV16/18) and performed RT-qPCR. We found that Nanog increases activity of both viral regulatory regions and elevates endogenous E6/E7 mRNA levels in cervical cancer-derived cells. We demonstrated by in vitro mutagenesis that changes at Nanog-binding sites found in the HPV18 LCR significantly inhibit transcriptional activation. Chromatin immunoprecipitation (ChIP) assays showed that Nanog binds in vivo to the HPV18 LCR, and its overexpression increases its binding as well as that of c-Jun. Surprisingly, we observed that mutation of AP1-binding sites also affect Nanog’s ability to activate transcription, suggesting cooperation between the two factors. We searched for putative Nanog-binding sites in the LCR of several HPVs and surprisingly found them only in those types associated with cancer development. Our study shows, for the first time, a role for Nanog in the regulation of E6/E7 transcription of HPV16/18.

sensitization by Ca 2þ . However, the molecular mechanism of the MCU's regulation by Ca 2þ remains unclear. Recently, MICU1 has been identified as an EF-hand-containing regulatory component of the MCU. We set out to elucidate the role of MICU1 in the Ca 2þ regulation of the MCU and to examine its possible contribution to the sensitization. Mitochondrial Ca2þ uptake was evaluated fluorometrically in suspensions of permeabilized MICU1 knockdown (MICU1KD) and control HeLa cells as ruthenium red-sensitive Ca 2þ clearance from the incubation buffer. Clearance of small Ca 2þ pulses elevating the [Ca 2þ ] to <1uM was rapid in MICU1KD cells, whereas it was negligible in control cells. Large Ca 2þ pulses increasing buffer [Ca 2þ ] to >10uM were taken up effectively by both MICU1KD and control cells. The dose-response for the clearance of added Ca 2þ was sigmoidal in the control cells. This was leftward-shifted and showed lesser cooperativity in the MICU1KD cells. MICU1KD rescue with wild type MICU1 restored the control type dose-response, whereas an EF-hand-mutant MICU1 shifted it to the right. When the time-dependent sensitization of the MCU was tested by a twopulse protocol, the MICU1KD failed to show a further increase in Ca 2þ sensitivity. As to the functional significance of altered Ca 2þ handling in MI-CU1KD, these cells displayed lesser Ca 2þ tolerance and more cell death under stress conditions. We propose that the MICU1, through its EF-hands, controls the [Ca 2þ ] set-point for MCU channel closure. MICU1 helps mitochondria to respond to physiological [Ca 2þ ] oscillations and provides some protection from Ca 2þ overloading.