Here we demonstrated that Pep2–Ae, an α-helix from the catalytic region of AKT1, disrupts the TRIB3/AKT1 interaction and reduces the cancer initiation capacity of luminal and basal BCCs, and primary BCCs from transgenic mice and PDX mice via the activation of FOXO1 phosphorylation, ubiquitination, and degradation, which leads to the inhibition of SOX2 expression and breast cancer stemness. The gene discussed is TRIB3; the disease is breast cancer.