The deficiency of Akt1 is sufficient to suppress tumor development in Pten+/- mice

Abstract

The tumor suppressor PTEN is frequently inactivated in human cancers. A major downstream effector of PTEN is Akt, which is hyperactivated via PTEN inactivation. It is not known, however, whether diminished Akt activity is sufficient to inhibit tumorigenesis initiated by Pten deficiency. Here we showed that the deficiency of Akt1 is sufficient to dramatically inhibit tumor development in Pten+/- mice. Akt1 deficiency had a profound effect on endometrium and prostate neoplasia, two types of human cancer, in which PTEN is frequently mutated, and also affected thyroid and adrenal medulla tumors and intestinal polyps. Even haplodeficiency of Akt1 was sufficient to markedly attenuate the development of high-grade prostate intraepithelial neoplasia (PIN) and endometrial carcinoma. These results have significant implications for cancer therapy.

Figure 1.

Akt1 deficiency impairs the development of high-grade PIN in Pten^+/− mice. (A) Paraffin-embedded anterior lobe sections derived from Pten^+/− mice were stained with either anti-pAkt or anti-PTEN. A PIN4 lesion (Lesion) and normal gland (N) are shown. (Insets) High magnification of an area for the lesion (L) or normal gland (N). (B) Incidence of PIN3 and PIN4 lesions in the three prostate lobes of Pten^+/−, Pten^+/−Akt1^+/−, and Pten^+/−Akt1^−/− mice. The number of mice in each group is indicated. (C) BrdU incorporation in the prostate lobes of Pten^+/−, Pten^+/−Akt1^+/−, and Pten^+/−Akt1^−/− mice. The number of mice in each group is indicated in parentheses. BrdU-positive cells were counted as described in Materials and Methods. P values were calculated for each prostate lobe in each genotype. (D) Increased expression of androgen receptor in PIN4 lesions in the anterior and dorsolateral lobes correlates with increased pAkt in the lesions. (Top panels) Immunostaining with anti-AR of paraffin-embedded sections derived form the anterior (A) and dorsolateral (DL) lobes of wild-type, Pten^+/−, and Pten^+/−Akt1^−/− mice. (Bottom panel) Immunostaining with anti-AR or anti-pAkt of serial sections derived from the anterior lobe of Pten^+/− mice. (Insets) High magnifications. (E) Immunoblot of protein extracts derived from wild-type and Akt1^−/− mouse prostates using anti-pAkt, anti-pan-Akt, and anti-β-actin.

Figure 2.

Akt1 deficiency is sufficient to inhibit the development of endometrial carcinoma in Pten^+/− mice. (A) Incidence of endometrial neoplasia in Pten^+/−, Pten^+/−Akt1^+/−, Pten^+/−Akt1^−/−, and wild-type mice. Total number of mice examined in each group is indicated in parentheses. (B) BrdU incorporation in the uteri of Pten^+/−, Pten^+/−Akt1^+/−, Pten^+/−Akt1^−/−, and wild-type mice. (Top panels) Representative areas of BrdU-positive cells. (C) Localization of FOXO1 in the uteri of Pten^+/−, Pten^+/−Akt1^+/−, and Pten^+/−Akt1^−/− mice. Representative sections immunostained with anti-FOXO1, showing strong cytoplasmic staining in the lesion of Pten^+/− uteri, both cytoplasmic and nuclear staining in Pten^+/−Akt1^+/− uteri, and mostly nuclear staining in Pten^+/−Akt1^−/− uteri. (Insets) High magnifications. (D) Immunostaining with anti-pS6 of uterus sections derived from Pten^+/−, wild-type, and Pten^+/−Akt1^−/− mice. Representative sections showing strong staining of pS6 in the luminal epithelium and the lesions in Pten^+/− uteri (100×, 250×, and 400×) that are confined only to the luminal epithelium (indicated by arrows) of wild-type and Pten^+/−Akt1^−/− uteri. CIS, stroma, and a normal gland (N) are indicated.

Figure 3.

Effect of Akt1 deficiency on tumor development in the adrenal and thyroid glands and on the number of polyps in the small intestine of Pten^+/− mice. (A) Quantification of BrdU incorporation in the adrenal medulla of Pten^+/− and Pten^+/−Akt1^−/− 11-mo-old male or 40-wk-old female mice. (B) Histopathological grades of the neoplastic lesions in adrenal medullas derived from Pten^+/−, Pten^+/−Akt1^−/−, and wild-type 11-mo-old male or 40-wk-old female mice. (C) Incidence of neoplastic lesions in thyroid glands derived from Pten^+/−, Pten^+/−Akt1^+/−, Pten^+/−Akt1^−/−, and wild-type 11-mo-old male mice. (D) The deficiency of Akt1 markedly reduced the number of polyps in the small intestine of Pten^+/− mice. Quantification of the number of intestinal polyps in 11-mo-old male mice (top panel) or 40-wk-old female mice (bottom panel). The number of polyps ± SD per mouse is shown. (E) Relative expression of Akt1, Akt2, and Akt3 mRNAs in prostate (lane 1), uterus (lane 2), adrenal gland (lane 3), thyroid (lane 4), colon (lane 5), intestine (lane 6), and in mouse embryo fibroblasts (lane 7).