Overexpression of 14-3-3ζ in cancer cells activates PI3K via binding the p85 regulatory subunit

Abstract

The ubiquitously expressed 14-3-3 proteins regulate many pathways involved in transformation. Previously, we found that 14-3-3ζ overexpression increased Akt phosphorylation in human mammary epithelial cells. Here, we investigated the clinical relevance and molecular mechanism of 14-3-3ζ overexpression-mediated Akt phosphorylation and the potential impact on breast cancer progression. We found that 14-3-3ζ overexpression was significantly (P = 0.005) associated with increased Akt phosphorylation in human breast tumors. Additionally, 14-3-3ζ overexpression combined with strong Akt phosphorylation was significantly (P=0.01) associated with increased cancer recurrence in patients. In contrast, knockdown of 14-3-3ζ expression by siRNA in cancer cell lines and tumor xenografts reduced Akt phosphorylation. Furthermore, 14-3-3ζ enhanced Akt phosphorylation through activation of PI3K. Mechanistically, 14-3-3ζ bound to the p85 regulatory subunit of PI3K and increased PI3K translocation to the cell membrane. A single 14-3-3 binding motif encompassing serine 83 on p85 is largely responsible for 14-3-3ζ-mediated p85 binding and PI3K/Akt activation. Mutation of serine 83 to alanine on p85 inhibited 14-3-3ζ binding to the p85 subunit of PI3K, reduced PI3K membrane localization and activation, impeded anchorage independent growth and enhanced stress induced apoptosis. These findings revealed a novel mechanism by which 14-3-3ζ overexpression activates PI3K, a key node in the mitogenic signaling network known to promote malignancies in many cell types.

The ShcA SH2 domain engages a 14-3-3/PI3′K signaling complex and promotes breast cancer cell survival

“…25 Thus, 14 --3 --3s is not likely to participate in the activation of pro-survival signaling downstream of the ShcA SH2 domain. We further demonstrate that 14 --3 --3z specifically co-immunoprecipitates with wild-type ShcA, and not the ShcR397K mutant, in mammary tumor lysates, which is consistent with the observation that 14 --3 --3z activates the PI3K/AKT pathway by recruiting the p85 regulatory subunit 19,26 (Figure 4d). However, we cannot exclude the possibility that one or more of the remaining 14 --3 --3 family members are recruited to the SH2 domain of ShcA to enhance breast cancer cell survival.…”

14-3-3 Proteins regulate Akt Thr308 phosphorylation in intestinal epithelial cells

“…This is a plausible scenario because proinflammatory cytokines can also affect other biological processes that control Akt function such as protein synthesis 2 and/or Akt targeting/shuttling, 2 which is known to be important for controlling Akt destiny and function. 39 14-3-3ζ stimulates PI3K signaling 59 and also activates PDK1, thus its presence could be important but not essential 60 to induce Akt activation, those properties in 14-3-3ζ could explain in part the tumor-promoting function attributed to 14-3-3ζ upregulation. 61 Additionally, the ratio maintained between the dimeric and monomeric forms of 14-3-3ζ might have a role in controlling Akt activity; and it is possible that oscillations in the amount of p14-3-3ζS58 are necessary not only to maintain the Akt signal but also to control its cellular localization, which is important because Akt phosphorylates at least 100 non-redundant substrates in different cell compartments.…”

Targeting 14-3-3zeta in cancer therapy

“…76 Previous study has showed that overexpression of 14-3-3zeta in cancer cells activates PI3K/ AKT signal. 77 FOBISIN101 could be developed as a new inhibitor of 14-3-3zeta, and serve as a novel agent for cancer intervention. Current 14-3-3zeta-targeting approaches are limited to knockdown experiments and peptide inhibitors, but discovering 14-3-3zeta-interacting molecules and developing a specific antibody or inhibitor that recognizes and blocks the functions or activation of 14-3-3zeta may indicate a new field for 14-3-3zeta-targeting therapy in clinical application.…”