High-content screening with siRNA optimizes a cell biological approach to drug discovery: defining the role of P53 activation in the cellular response to anticancer drugs

Deciphering the effects of compounds on molecular events within living cells is becoming an increasingly important component of drug discovery. In a model application of the industrial drug discovery process, the authors profiled a panel of 22 compounds using hierarchical cluster analysis of multiparameter high-content screening measurements from nearly 500,000 cells per microplate. RNAi protein knockdown methodology was used with high-content screening to dissect the effects of 2 anticancer drugs on multiple target activities. Camptothecin activated p53 in A549 lung carcinoma cells pretreated with scrambled siRNA, exhibited concentration-dependent cell cycle blocks, and induced moderate microtubule stabilization. Knockdown of camptothecin-induced p53 protein expression with p53 siRNA inhibited the G1/S blocking activity of the drug and diminished its microtubule-stabilizing activity. Paclitaxel activated p53 protein at low concentrations but exhibited G2/M cell cycle blocking activity at higher concentrations where microtubules were stabilized. In cells treated with p53 siRNA, paclitaxel failed to activate p53 protein, but the knockdown did not have a significant effect on the ability of paclitaxel to stabilize microtubules or induce a G2/M cell cycle block. Thus, this model application of the use of RNAi technology within the context of high-content screening shows the potential to provide massive amounts of combinatorial cell biological information on the temporal and spatial responses that cells mount to treatment by promising therapeutic candidates.     

Species-specific measurements of ectomycorrhizal turnover under N-fertilization: combining isotopic and genetic approaches

Ectomycorrhizal fungi play a significant role in the transfer of nutrients between plant and soil pools. Here we combine natural abundance ¹⁴C measurements with restriction fragment length polymorphism (RFLP) to study the effects of nitrogen fertilization on the residence time of carbon within ectomycorrhizal species. We show that the carbon in ectomycorrhizal fungi turns over every 4–5 years, indicating that these fungi are relatively long-lived. Moreover, ectomycorrhizal fungi responded in a species-specific way to fertilization. Cenococcum geophilum contained younger carbon on average in nitrogen-fertilized plots than in control plots, even though turnover rates of the community as a whole did not shift significantly. Our results suggest that the response of ectomycorrhizal fungi to N availability is complex, and alterations in tissue turnover within this microbial pool may vary depending on community structure.     

Ouabain-insensitive salt and water movements in duck red cells. II. The role of chloride in the volume response

This paper describes the effect of external chloride on the typical swelling response induced in duck red cells by hypertonicity or norepinephrine. Lowering chloride inhibits swelling and produces concomitant changes in net movements of sodium and potassium in ouabain-treated cells, which resemble the effect of lowering external sodium or potassium. Inhibition is the same whether chloride is replaced with gluconate or with an osmotic equivalent of sucrose. Since changes in external chloride also cause predictable changes in cell chloride, pH, and water, these variables were systematically investigated by varying external pH along with chloride. Lowering pH to 6.60 does not abolish the response if external chloride levels are normal, although the cells are initially swollen due to the increased acidity. Cells deliberately preswollen in hypotonic solutions with appropriate ionic composition can also respond to norepinephrine by further swelling. These results rule out initial values of cell water, chloride, and pH as significant variables affecting the response. Initial values of the chloride equilibrium potential do have marked effect on the direction and rate of net water movement. If chloride is lowered by replacement with the permeant anion, acetate, E(Cl) is unchanged and a normal response to norepinephrine, which is inhibited by furosemide, is observed. Increasing internal sodium by the nystatin technique also inhibits the response. A theory is developed which depicts that the cotransport carrier proposed in the previous paper (W.F. Schmidt and T.J. McManus. 1977b. J. Gen. Physiol. 70:81-97) moves in response to the net electrochemical potential difference driving sodium and potassium across the membrane. Predictions of this theory fit the data for both cations and anions.     

Understanding Smallholder Participation in Payments for Ecosystem Services: the Case of Costa Rica

This paper uses household survey data to examine factors associated with smallholder households that enroll in Costa Rica’s longstanding payments for ecosystem services (PES) program. To date, most evaluations of this sort have focused on larger landowners. Results from this study show that smallholders enrolled in PES tend to be older, wealthier, and have access to non-farm salaried income. These features match enrollment patterns of larger landowners in that enrollees tend to be relatively wealthy and only marginally engaged in agriculture. In addition, smallholders on state agrarian reform lands are significantly less likely to enroll in PES. These results indicate that targeting PES toward smaller landowners does not necessarily equate to a policy that reaches the rural poor, and suggests that further work is needed to address the access barriers to this program for economically marginal landowners.