Radiation therapy is an effective
cancer treatment modality although
tumors invariably become resistant. Using the transgenic
adenocarcinoma of mouse prostate (TRAMP) model system, we report that a hypofractionated radiation schedule (10 Gy/day for 5 consecutive days) effectively blocks prostate
tumor growth in wild type (β1wt /TRAMP) mice as well as in mice carrying a conditional ablation of β1
integrins in the prostatic epithelium (β1pc-/- /TRAMP). Since JNK is known to be suppressed by β1
integrins and mediates radiation-induced apoptosis, we tested the effect of
SP600125, an inhibitor of
c-Jun amino-terminal kinase (JNK) in the TRAMP model system. Our results show that
SP600125 negates the effect of radiation on
tumor growth in β1pc-/- /TRAMP mice and leads to invasive
adenocarcinoma. These effects are associated with increased
focal adhesion kinase (FAK) expression and phosphorylation in prostate
tumors in β1pc-/- /TRAMP mice. In marked contrast, radiation-induced
tumor growth suppression, FAK expression and phosphorylation are not altered by
SP600125 treatment of β1wt /TRAMP mice. Furthermore, we have reported earlier that abrogation of
insulin-like growth factor receptor (IGF-IR) in
prostate cancer cells enhances the sensitivity to radiation. Here we further explore the β1/IGF-IR crosstalk and report that β1
integrins promote cell proliferation partly by enhancing the expression of IGF-IR. In conclusion, we demonstrate that β1
integrin-mediated inhibition of JNK signaling modulates
tumor growth rate upon hypofractionated radiation.