The was to identify PI3K mTOR p70S6K pathway down stream secondly targets using gene expression profiling for breast cancer cell lines that we have previously characterized in regard to copy number and gene expression. Five Inhibitors,Modulators,Libraries breast cancer cell lines were treated with PI3K mTOR pathway inhibitors, including two cell lines that were also inhibited with three RPS6KB1 siRNAs, since these Inhibitors,Modulators,Libraries two cell lines show a high level expression of p70S6K. The gene expression signatures responsive to both PI3K mTOR pathway and p70S6K inhibitions revealed previously uni dentified genes suggesting novel downstream targets for PI3K mTOR p70S6K pathway. The PI3K pathway is deregulated in a number of cancers and clinical trials are currently attempting to target differ ent components of this pathway.
The activation of PI3K pathway is associated with aggressive breast cancer and therefore, identification of its downstream targets may have Inhibitors,Modulators,Libraries diagnostic value. Since p70S6K is a down stream mediator of PI3K pathway, we explored gene expression alterations caused by both p70S6K and PI3K mTOR pathway inhibitions. Altogether, expression levels of 17 genes were altered in both RPS6KB1 suppressed and inhibitor treated samples, including VTCN1 B7 H4, CDKN2B, SCD and ARL11. Especially, the down regula tion of VTCN1 B7 H4 is interesting, since it has recently been found to be overexpressed in a number of cancers and have also been linked to poor prognosis. The expression of B7 H1, which is a member of the same pro tein family, has been shown to be increased due to loss of PTEN and activation of PI3K pathway, linking PTEN with immunoresistance mediated in part by B7 H1.
The down regulation of VTCN1 B7 H4 due to Ly294002 treat ment suggests that similar to Inhibitors,Modulators,Libraries B7 H1, B7 H4 is also regu lated by PI3K. CDKN2B, encoding for cyclin dependent kinase inhibitor 2B, was up regulated after mTOR and p70S6K inhibitions in BT 474. Similarly, CDKN2A, was up regulated in MCF 7 in response to p70S6K suppres sion but not with inhibition of mTOR. The p16 p15 pro teins encoded by CDKN2A CDKN2B are known to be associated with telomerase activation and cancer progres sion as well as to induce cell cycle arrest by inhibi tion of CDK4 kinase. Interestingly, mTOR inhibition caused significant down regulation of CCND1 suggesting that cell cycle arrest could be caused by either down or up regulation of genes activating or inhibiting CDK4.
Additionally, SCD was down regulated after mTOR inhi bition with rapamycin and p70S6K suppression with RPS6KB1 siRNAs. SCD encodes stearoyl CoA desaturase, which has been suggested to promote cell proliferation, invasion and inhibition Inhibitors,Modulators,Libraries of apoptosis. Our finding of SCD as a potential downstream target of PI3K mTOR p70S6K pathway is supported by the study of Chang et al, which reported that SCD is selleck chem activated by PI3K and inhib ited by Ly294002.