Cannibalism stress response in Bacillus subtilis.

When faced with carbon source limitation, the Gram-positive soil organism Bacillus subtilis initiates a survival strategy called sporulation, which leads to the formation of highly resistant endospores that allow B. subtilis to survive even long periods of starvation. In order to avoid commitment to this energy-demanding and irreversible process, B. subtilis employs another strategy called 'cannibalism' to delay sporulation as long as possible. Cannibalism involves the production and secretion of two cannibalism toxins, sporulation delaying protein (SDP) and sporulation killing factor (SKF), which are able to lyse sensitive siblings. The lysed cells are thought to then provide nutrients for the cannibals to slow down or even prevent them from entering sporulation. In this study, we uncovered the role of the cell envelope stress response (CESR), especially the Bce-like antimicrobial peptide detoxification modules, in the cannibalism stress response during the stationary phase. SDP and SKF specifically induce Bce-like systems and some extracytoplasmic function σ factors in stationary-phase cultures, but only the latter provide some degree of protection. A full Bce response is only triggered by mature toxins, and not by toxin precursors. Our study provides insights into the close relationship between stationary-phase survival and the CESR of B. subtilis.

Antitumoral effects of calcitriol in basal cell carcinomas involve inhibition of hedgehog signaling and induction of vitamin D receptor signaling and differentiation.

Activation of the Hedgehog (Hh)-signaling pathway due to deficiency in the Hh receptor Patched1 (Ptch) is the pivotal defect leading to formation of basal cell carcinoma (BCC). Recent reports provided evidence of Ptch-dependent secretion of vitamin D(3)-related compound, which functions as an endogenous inhibitor of Hh signaling by repressing the activity of the signal transduction partner of Ptch, Smoothened (Smo). This suggests that Ptch-deficient tumor cells are devoid of this substance, which in turn results in activation of Hh-signaling. Here, we show that the application of the physiologically active form of vitamin D(3), calcitriol, inhibits proliferation and growth of BCC of Ptch mutant mice in vitro and in vivo. This is accompanied by the activation of the vitamin D receptor (Vdr) and induction of BCC differentiation. In addition, calcitriol inhibits Hh signaling at the level of Smo in a Vdr-independent manner. The concomitant antiproliferative effects on BCC growth are stronger than those of the Hh-specific inhibitor cyclopamine, even though the latter more efficiently inhibits Hh signaling. Taken together, we show that exogenous supply of calcitriol controls the activity of 2 independent pathways, Hh and Vdr signaling, which are relevant to tumorigenesis and tumor treatment. These data suggest that calcitriol could be a therapeutic option in the treatment of BCC, the most common tumor in humans.