Figure 7. GDF15 promotes radioresistant tumors in mice, along with SMAD activation and stemness conversion.

A total of 4×10⁶ KB cells, with or without pre-treatment with the rhGDF15 protein (20 ng/ml for 5 days), were subcutaneously injected into BALB/c mice (10 mice each group) in the upper portion of the hind limb. At day 14, each group was randomly divided into two groups (5 mice per group), with or without receiving 2 Gy of irradiation, followed by repeated irradiation of the same dose twice a week for a total of 8 Gy. A. Tumor volume was measured twice a week and calculated as (length x width x height) for 36 days. B-D. The tumors in the group of irradiation, either with or without pre-treatment of rhGDF15, were dissected. The protein expression levels of SMAD family molecules in the rhGDF15 treatment tumor group (B) or the control groups (C) were determined by using western blot analysis, and quantified the relative expression levels after normalized with GAPDH (D). E. The expression levels of ALDH1 and Nestin in tumor tissues were determined by using IHC analysis. Three tumor sections of IHC staining were shown for examples (*: p < 0.05, **: p < 0.01, ***: p < 0.001, t-test).