Crosstalk of moderate ROS and PARP-1 contributes to sustainable proliferation of conditionally reprogrammed keratinocytes.

Conditionally reprogrammed cell (CRC) technique is a promising model for biomedical and toxicological research. In the present study, our data first demonstrated an increased level of PARP-1 in conditionally reprogrammed human foreskin keratinocytes (CR-HFKs). We then found that PARP inhibitor ABT-888 (ABT), reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC), or combination (ABT + NAC) were able to inhibit cell proliferation, ROS, PARP-1, and ROS related protein, NRF2, and NOX1. Interestingly, knockdown of endogenous PARP-1 significantly inhibited cell proliferation, indicating that the increased PARP-1 expression was critical for CR. Importantly, we found that a moderate level of ROS contributed the cell proliferation and increased PARP-1 since knockdown of PARP-1 also inhibited the ROS. The similar inhibition of cell proliferation, ROS, and expression of PARP-1 and NRF2 proteins was observed when CR-HFKs were treated with hydroquinone (HQ), a key component from skin-lightening products. Moreover, the treatment of HQ plus treatment of ABT, NAC, or combination can further inhibit cell proliferation, ROS, expression of PARP-1, and NRF2 proteins. PARP-1 knockdown inhibited the population doubling (PDL) and treatment of HQ inhibited the PDL further, as well as the change of ROS. Finally, we discovered that pathways including cyclin D1, NRF2, Rb and pRb, CHK2, and p53, were involved in cell proliferation inhibition with HQ. Taken together, our findings demonstrated that crosstalk between ROS and PARP-1 involves in the cell proliferation in CR-HFKs, and that inhibition of CR-HFK proliferation with HQ is through modulating G1 cell cycle arrest.