Specific TCP transcription factors interact with and stabilize PRR2 within different nuclear sub-domains.

Plants possess a large set of transcription factors both involved in the control of plant development or in plant stress responses coordination. We previously identified PRR2, a Pseudo-Response Regulator, as a plant-specific CML-interacting partner. We reported that PRR2 acts as a positive actor of plant defense by regulating the production of antimicrobial compounds. Here, we report new data on the interaction between PRR2 and transcription factors belonging to the Teosinte branched Cycloidea and PCF (TCP) family. TCPs have been described to be involved in plant development and immunity. We evaluated the ability of PRR2 to interact with seven TCPs representative of the different subclades of the family. PRR2 is able to interact with TCP13, TCP15, TCP19 and TCP20 in yeast two-hybrid system and in planta interactions were validated for TCP19 and TCP20. Transient expression in tobacco highlighted that PRR2 protein is more easily detected when co-expressed with TCP19 or TC20. This stabilization is associated with a specific sub-nuclear localization of the complex in Cajal bodies or in nuclear speckles according to the interaction of PRR2 with TCP19 or TCP20 respectively. The interaction between PRR2 and TCP19 or TCP20 would contribute to the biological function in specific nuclear compartments.

Evaluation of THP-1 cell line as an in vitro model for long-term safety assessment of new molecules.

OBJECTIVE: Monitoring the chronic and subacute toxicity is essential in the development of new cosmetic ingredients. In response to the present lack of validated alternative methods, we developed an in vitro model for repeated dose cytotoxicity on THP-1 cells. METHODS: Cultured in suspension, cells were treated with chemicals for 14 days with a frequency of three applications per week, and cell viability was determined by MTT assay. We first investigated the long-term effects of chemicals that induce different kinds of cytotoxicity: Paraquat (PQ), 3-Nitropropanoic acid (3-NPA) and sodium dodecyl sulphate (SDS). From acute studies, doses between 1 and 10 µg ml(-1) were chosen to perform our subacute cytotoxicity assay. Comparative genotoxicity evaluations were made with H2 O2 or Paraquat treated TPH-1 cells. Comet assays were performed at 1 h (4°C); after a 24-h recovery period (37°C); and finally, after a long-term period of treatment (14 days, 37°C).Once adapted to plant extracts or highly diluted molecules, some of our cosmetic compounds were tested with this model. RESULTS: As expected, after 14 days of treatment with Paraquat, cell viability rates dramatically decreased for doses as low as 3 µg ml(-1) , whereas 10 µg ml(-1) of 3-NPA and SDS did not induce more than 44% of cell death. Surprisingly, after subacute treatment, comet assay results revealed a dose-dependent increase in tail moments for Paraquat, whereas those of H2 O2 remained low. Moreover, all our compounds tested at 0.5-5 µg ml(-1) were classified as safe, even with a cut-off at 90% of cell viability. CONCLUSION: In conclusion, this assay could be of interest for subacute cytotoxicity and genotoxic assessment of daily and topically applied products and suggests that PQ is a choice worthy positive control.