For example, ARL11, a gene with recently identified tumor suppressor function, was up regulated after both kinase inhibitor Tipifarnib inhibiting PI3K and suppression of p70S6K. Taken together, Inhibitors,Modulators,Libraries our study suggests many novel targets potentially regulated by PI3K mTOR p70S6K pathway. Overall, the number of overlapping genes between three treatments was small, Inhibitors,Modulators,Libraries which is expected, since all the inhibitors have different targets with cross talk also with multiple other pathways. In addition to these biological reasons, there are technical differences that are likely to cause variability for gene expression changes caused by different inhibitors. These include different specificities, efficiencies and mechanisms of action of the treatments as well as differences in assay platforms.
For example, Ly294002 is not exclusively selective for the PI3Ks, but is known to inhibit also other lipid kinases than just PI3K. Secondly, possible off target effects of RPS6KB1 siRNA knock down or the fact that knock down mainly resulted in 70% decrease in mRNA levels are possible rea sons for variability Inhibitors,Modulators,Libraries between different experiments. Finally, inhibitor treated samples were studied using a 17 K gene expression microarray platform, whereas siRNA treated samples were hybridized on a 44 K microarray platform causing slight differences in the gene content of these two microarray platforms. To minimize the above mentioned effects, we took into account only those genes that were differentially expressed by at least two different siRNAs and correlated this information with genes responsive to PI3K and or mTOR inhibition.
This led to the identifica tion of 17 genes that are potential targets of PI3K mTOR p70S6K pathway. Since PI3K mTOR pathway has a central role in cell sur vival and p70S6 kinase is an important regulator of cell cycle progression through the G1 S point, we further stud ied the effect of Ly294002 and rapamycin on apoptosis and cell Inhibitors,Modulators,Libraries cycle. Ly294002 treatment, but not rapamycin, induced apoptosis of the breast cancer cell lines, which may be due to a number of different reasons. Ly294002 inhibits PI3K that further regulates AKT, which has a number of targets that are involved in cell death and sur vival. In contrast, rapamycin inhibits mTOR, which is located downstream of AKT and therefore, AKT mediated effects on apoptosis should not be detected after rapamy cin treatment.
Additionally, mTOR has been shown to be involved in Notch1 mediated inhibition of p53 induced apoptosis. Since the majority of the breast cancer cell lines used in this study carry a mutated form of p53, Inhibitors,Modulators,Libraries inhibition of mTOR by rapamycin should not affect on p53 induced cell death. Rapamycin also inhibits the phosphorylation and activation of p70S6K through mTOR inhibition. citation It has been observed that the breast cancer cell lines with an amplification of RPS6KB1 are more sensitive to rapamycin than cells with no amplifica tion.