P70S6K and Elf4E Dual Inhibition Is Essential to Control Bladder Tumor Growth and Progression in Orthotopic Mouse Non-muscle Invasive Bladder Tumor Model

We investigated how the dual inhibition of the molecular mechanism of the mammalian target of the rapamycin (mTOR) downstreams, P70S6 kinase (P70S6K) and eukaryotic initiation factor 4E (eIF4E), can lead to a suppression of the proliferation and progression of urothelial carcinoma (UC) in an orthotopic mouse non-muscle invasive bladder tumor (NMIBT) model. A KU-7-luc cell intravesically instilled orthotopic mouse NMIBC model was monitored using bioluminescence imaging (BLI) in vivo by interfering with different molecular components using rapamycin and siRNA technology. We then analyzed the effects on molecular activation status, cell growth, proliferation, and progression. A high concentration of rapamycin (10 microM) blocked both P70S6K and elF4E phosphorylation and inhibited cell proliferation in the KU-7-luc cells. It also reduced cell viability and proliferation more than the transfection of siRNA against p70S6K or elF4E. The groups with dual p70S6K and elF4E siRNA, and rapamycin reduced tumor volume and lamina propria invasion more than the groups with p70S6K or elF4E siRNA instillation, although all groups reduced photon density compared to the control. These findings suggest that both the mTOR pathway downstream of eIF4E and p70S6K can be successfully inhibited by high dose rapamycin only, and p70S6K and Elf4E dual inhibition is essential to control bladder tumor growth and progression.

P70S6K and Elf4E Dual Inhibition Is Essential to Control Bladder Tumor Growth and Progression in Orthotopic Mouse Non-muscle Invasive Bladder Tumor Model

We investigated how the dual inhibition of the molecular mechanism of the mammalian target of the rapamycin (mTOR) downstreams, P70S6 kinase (P70S6K) and eukaryotic initiation factor 4E (eIF4E), can lead to a suppression of the proliferation and progression of urothelial carcinoma (UC) in an orthotopic mouse non-muscle invasive bladder tumor (NMIBT) model. A KU-7-luc cell intravesically instilled orthotopic mouse NMIBC model was monitored using bioluminescence imaging (BLI) in vivo by interfering with different molecular components using rapamycin and siRNA technology. We then analyzed the effects on molecular activation status, cell growth, proliferation, and progression. A high concentration of rapamycin (10 microM) blocked both P70S6K and elF4E phosphorylation and inhibited cell proliferation in the KU-7-luc cells. It also reduced cell viability and proliferation more than the transfection of siRNA against p70S6K or elF4E. The groups with dual p70S6K and elF4E siRNA, and rapamycin reduced tumor volume and lamina propria invasion more than the groups with p70S6K or elF4E siRNA instillation, although all groups reduced photon density compared to the control. These findings suggest that both the mTOR pathway downstream of eIF4E and p70S6K can be successfully inhibited by high dose rapamycin only, and p70S6K and Elf4E dual inhibition is essential to control bladder tumor growth and progression.

Synergistic activation of p70S6 kinase associated with stem cell factor in MO7e cells

Stem cell factor (SCF) is an early-acting cytokine inducing proliferative synergy with other cytokines in hematopoietic cells. We earlier showed that p21 was synergistically induced in SCF synergy and the p44/42 MAPK pathway was essential for the transcriptional control of p21. SCF synergy accompanies protein synthesis. p70S6K implicated in translational control in many other systems has not been shown in SCF synergy induced system. GM-CSF dependent human cell line MO7e was stimulated with GM-CSF with SCF, and investigated activation of p70S6K by using phospho-specific antibody. A possible contribution of p70S6K to SCF synergy was examined by measuring p21 induction as a model system. p70S6K was slightly activated by GM-CSF alone and markedly activated by SCF alone. Combined stimulation with these two cytokines synergistically activated p70S6K resulting in persistent activation. Addition of the pathway- specific inhibitors for PI3K or FRAP/TOR, two upstream pathways of p70S6K resulted in abolishment of p70S6K phosphorylation and also significant reduction of p21 protein level. These data suggest that synergistically activated p70S6K by GM-CSF plus SCF involves, at least in part, protein translational control including regulation of p21 protein.