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The nicotinamide adenine dinucleotide (NAD)-dependent deacetylase Sir2 (silent information regulator 2) regulates gene silencing in yeast and promotes lifespan extension during caloric restriction. The mammalian homologue of Sir2 (SirT1) regulates p53, NF-κB and Forkhead transcription factors, and is implicated in stress response. This report shows that the cell-cycle and apoptosis regulator E2F1 induces SirT1 expression at the transcriptional level. Furthermore, SirT1 binds to E2F1 and inhibits E2F1 activities, forming a negative feedback loop. Knockdown of SirT1 by small interference RNA (siRNA) increases E2F1 transcriptional and apoptotic functions. DNA damage by etoposide causes E2F1-dependent induction of SirT1 expression and knockdown of SirT1 increases sensitivity to etoposide. These results reveal a mutual regulation between E2F1 and SirT1 that affects cellular sensitivity to DNA damage. [ABSTRACT FROM AUTHOR]

An endophytic fungus, Aspergillus niger, isolated from the inner bark of a Taxus chinensis tree, was used as an elicitor to stimulate the Taxol (paclitaxel) production in a Taxus chinensis cell suspension culture. Different elicitor doses and elicitation times were tested in a batch culture; and the highest volumetric Taxol yield was achieved when 40 mg of the fungal elicitor (carbohydrate equivalent) l–1 was added to the culture during the late exponential-growth phase. The elicitation resulted in a more than two-fold increase in the Taxol yield and about a six-fold increase in total secretion. The Taxol yield was further improved substantially by applying medium renewal and re-elicitation to the culture. In particular, with repeated medium renewal (in a way similar to medium perfusion) and a second elicitation of the culture, the volumetric Taxol yield was increased to 67.1±7.5 mg l–1, which was about seven times the amount obtained in the non-elicited batch culture. The Taxol productivity of the perfusion-like culture with repeated fungal elicitation was 1.5 mg l–1 day–1, which was about 40% higher than that of the elicitor-treated batch culture and three times the productivity of the non-elicited batch culture. [ABSTRACT FROM AUTHOR]