PTEN (phosphatase and
tensin homologue deleted on chromosome ten)/PI3K (
phosphatidylinositol 3-kinase)/Akt/mTOR (
mammalian target of rapamycin) signaling pathway, which is commonly dysregulated in a broad array of human
malignancies, controls the assembly of eukaryotic translation
initiation factor 4F (
eIF4F) complex through regulation of
eIF4E binding proteins (4E-BPs) phosphorylation. And accumulated data over the past two decades implicated
eIF4F complex as one of the promising targets for anticancer
therapy. It has been confirmed that the translation initiation of
mRNA coding for
hypoxia-inducible factor-1α (HIF-1α) and
survivin, which had been considered as the two major determinants of
tumor radiosensitivity, are both controlled by
eIF4F complex. Also,
eIF4F complex controls the expression of
VEGF and bFGF, the two well-known pro-angiogenic factors involved in developing radioresistance. Therefore
eIF4F complex plays a pivotal role in regulation of radiosensitivity. In this article, we postulate that cell-permeable, phosphorylation-defective 4E-BP fusion
proteins, which could be prepared by substituting the mTOR recognition motif located in N-terminal of 4E-BPs with
protein transduction domain from HIV-1 TAT,
HSV-1 VP22 or PTD4, could not only inhibit
tumor growth but also enhance
tumor response to
radiation therapy through disruption of
eIF4F complex assembly. In our opinion, the
recombinant fusion proteins are superior to
mTOR inhibitors for they do not cause immunosuppression, do not lead to Akt activation, and could be easily prepared by prokaryotic expression. If the hypothesis was proved to be practical, the cell-permeable, phosphorylation-defective 4E-BP fusion
proteins would be widely used in clinical settings to improve
tumor response to
radiotherapy in the near future.