demonstrated that 14-3-3 gamma interacts with diverse proteins and that this interaction is strengthened by AKT , suggesting that AKT may act upstream of 14-3-3 and that they are connected to cancer progression .
Although PPAR[gamma] ligands and/or its antagonists induce apoptosis in cancer cells, including glioblastoma cells [9,10, 12], the link between 14-3-3 gamma and BIS in GSC-like spheres is not well defined.
In this study, we describe the effect of a combination treatment with PPAR[gamma] ligands and its inhibitor GW9662 on spheres of glioblastoma cells through downregulation of BIS and 14-3-3 gamma levels, as well as inhibition of SOX2, MMP2 activity, and sphere-forming activity without enhancing the levels of cleaved poly(ADP-ribose) polymerase (PARP).
Cotreatment with PPAR[gamma] Ligand and GW9662 Decreased BIS, 14-3-3 Gamma, and SOX2 Together with Reduced Phosphorylation of STAT3 and AKT.
To address whether downregulation of BIS and 14-3-3 gamma by combined treatment with PPAR[gamma] ligands and GW9662 sensitizes glioblastoma cells towards inhibition of proliferation, we performed knockdown experiments silencing BIS and 14-3-3 gamma.
Finally, we examined whether 14-3-3 gamma or BIS depletion using siRNA affects sphere-forming activity.
In this study, we demonstrated that a combined treatment with PPAR[gamma] ligand and its inhibitor GW9662 downregulated BIS and 14-3-3 gamma expression and decreased phosphorylation of STAT3 and AKT, leading to inhibition of GSClike spheres and SOX2 expression (Figure 4).
We tested whether si-14-3-3 beta and gamma affect sphere-forming activity and found that single treatment with si-14-3-3 gamma led to moderately reduced sphere-forming activity compared to si-14-3-3 beta (data not shown), meaning that 14-3-3 gamma may play a significant role in glioblastoma stemness.
Although BIS forms an immunoreactive complex with 14-3-3 zeta , suggesting that BIS may affect BAD directly or indirectly through 14-3-3, we did not find that BIS or 14-3-3 gamma depletion enhanced PPAR[gamma] ligand-induced PARP cleavage.
Combination treatment of GCSs with PPAR[gamma] ligand and its inhibitor GW9662 inhibited stem-like properties via downregulation of BIS and 14-3-3 gamma levels together with decreased SOX2 and MMP2 activity without enhancing PARP cleavage.