Figure 3.

STAT3 suppresses PTEN deficiency-induced malignant cell transformation. (A,B) Stat3^loxP/loxP;PTEN^shRNA or Stat3^−/−;PTEN^shRNA astrocytes were injected subcutaneously into SCID mice. Eight weeks after injection, tumors were removed, measured, and stained. STAT3 loss induced an increase in tumor size as revealed by hematoxylin and eosin (H&E) staining (A) and tumor size measurements (n = 8; t-test, [*] P < 0.05) (B). Arrows in A show the tumor limits. Bar, 1 mm. (C) Histologic analysis of the Stat3^−/−;PTEN^shRNA tumors by H&E staining. The tumors showed histologic features of neoplastic transformation including nuclear atypia, pleomorphism, and frequent mitotic figures (arrowheads). Bar, 100 μm. (D) Nestin and Ki67 immunostaining of Stat3^loxP/loxP;PTEN^shRNA and Stat3^−/−;PTEN^shRNA tumors. These tumors express nestin, a characteristic marker of glial tumors. Cell proliferation rate, as measured by the percentage of Ki67-positive cells, was higher in Stat3^−/−;PTEN^shRNA tumors as compared with Stat3^loxP/loxP;PTEN^shRNA tumors (64% vs. 25%, respectively; average of two tumors each). Bar, 100 μm.