Evidence for heightened hexokinase II immunoexpression in hepatocyte dysplasia and hepatocellular carcinoma.

BACKGROUND: Normal hepatocytes exhibit low-affinity hexokinase (glucokinase [HKIV]), but during oncogenesis, there is a switch from HKIV to HKII expression. The aims of this study were to compare the immunoexpression of HKII in non-dysplastic cirrhosis (NDC), liver cell change/dysplasia in cirrhosis (LCD), HCC, and normal liver control tissues, and to correlate HKII expression with clinical and histopathological parameters. DESIGN: Immunohistochemistry was performed on a liver cancer progression tissue array consisting of specimens from explants with cirrhosis, including 45 tissue samples with HCC, 108 without HCC, 143 with LCD, and 8 normal liver control tissues. HKII expression was quantified as positive pixel counts/square millimeter (ppc/mm(2)) by image analysis. RESULTS: There was a stepwise increase in HKII level from normal liver tissue to NDC, to LCD, and to HCC (p = 0.001). HKII levels were significantly higher in areas of LCD versus NDC (p ≤ 0.001), and in LCD and HCC versus NDC (p = 0.007). HKII levels were similar in LCD and HCC (p = 0.124). HKII levels were higher in grade 2-4 versus grade 1 HCCs (p = 0.044), and in pleomorphic versus non-pleomorphic HCC variants (p = 0.041). Higher levels of HKII expression in LCD and HCC versus NDC and in higher tumor grade remained significant in multivariate analysis. CONCLUSIONS: Higher levels of HKII immunoexpression in LDC and HCC compared with NDC suggest that upregulation of HKII occurs during the process of hepatocarcinogenesis in humans. In HCC, higher levels of HKII are associated with more aggressive histological features.

Leptin deficiency and beta-cell dysfunction underlie type 2 diabetes in compound Akt knockout mice.

Phenotypic analyses of mice null for the individual Akt isoforms suggested that they are functionally distinct and that only Akt2 plays a role in diabetes. We show here that Akt isoforms play compensatory and complementary roles in glucose homeostasis and diabetes. Insulin resistance in Akt2(-/-) mice was inhibited by haplodeficiency of Pten, suggesting that other Akt isoforms can compensate for Akt2 function. Haplodeficiency of Akt1 in Akt2(-/-) mice, however, converts prediabetes to overt type 2 diabetes, which is also reversed by haplodeficiency of Pten. Akt3 does not appear to contribute significantly to diabetes. Overt type 2 diabetes in Akt1(+/-) Akt2(-/-) mice is manifested by hyperglycemia due to beta-cell dysfunction combined with impaired glucose homeostasis due to markedly decreased leptin levels. Restoring leptin levels was sufficient to restore normal blood glucose and insulin levels in Akt1(+/-) Akt2(-/-) and Akt2(-/-) mice, suggesting that leptin-deficiency is the predominant cause of diabetes in these mice. These results uncover a new mechanism linking Akt to diabetes, provide a therapeutic strategy, and show that diabetes induced as a consequence of cancer therapy, via Akt inhibition, could be reversed by leptin therapy.

Immunohistochemical expression of components of the Akt-mTORC1 pathway is associated with hepatocellular carcinoma in patients with chronic liver disease.

UNLABELLED: Activation of the Akt-mTORC1 signaling pathway was evaluated in premalignant and hepatocellular carcinoma (HCC) lesions by assessing the expression of pS6, an Akt effector, and PTEN, an Akt suppressor. METHODS: Immunohistochemical staining for pS6 and PTEN was performed on liver tissue from 52 patients with cirrhosis, with and without HCC. Two pathologists independently evaluated pS6 staining on a semiquantitative scale and categorized PTEN staining as present or absent. RESULTS: In the HCC group, pS6 staining was greatest in HCC, followed by dysplasia, and benign cirrhotic tissue (P < 0.001). pS6 staining was greater in cirrhotic tissue from patients with HCC compared to cirrhosis in patients without HCC (P = 0.03). PTEN staining in tumor was absent in 8/33 (24%) cases. Loss of PTEN expression was more common in patients with higher tumor stage, compared to those with stage 1 tumors (P = 0.04). CONCLUSION: Immunohistochemical evidence of activation of the Akt-mTORC1 pathway is associated with HCC.

Akt determines replicative senescence and oxidative or oncogenic premature senescence and sensitizes cells to oxidative apoptosis.

Akt deficiency causes resistance to replicative senescence, to oxidative stress- and oncogenic Ras-induced premature senescence, and to reactive oxygen species (ROS)-mediated apoptosis. Akt activation induces premature senescence and sensitizes cells to ROS-mediated apoptosis by increasing intracellular ROS through increased oxygen consumption and by inhibiting the expression of ROS scavengers downstream of FoxO, particularly sestrin 3. This uncovers an Achilles' heel of Akt, since in contrast to its ability to inhibit apoptosis induced by multiple apoptotic stimuli, Akt could not inhibit ROS-mediated apoptosis. Furthermore, treatment with rapamycin that led to further Akt activation and resistance to etoposide hypersensitized cancer cells to ROS-mediated apoptosis. Given that rapamycin alone is mainly cytostatic, this constitutes a strategy for cancer therapy that selectively eradicates cancer cells via Akt activation.

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

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.

Dwarfism, impaired skin development, skeletal muscle atrophy, delayed bone development, and impeded adipogenesis in mice lacking Akt1 and Akt2.

To elucidate the functions of the serine/threonine kinase Akt/PKB in vivo, we generated mice lacking both akt1 and akt2 genes. Akt1/Akt2 double-knockout (DKO) mice exhibit severe growth deficiency and die shortly after birth. These mice display impaired skin development because of a proliferation defect, severe skeletal muscle atrophy because of a marked decrease in individual muscle cell size, and impaired bone development. These defects are strikingly similar to the phenotypes of IGF-1 receptor-deficient mice and suggest that Akt may serve as the most critical downstream effector of the IGF-1 receptor during development. In addition, Akt1/Akt2 DKO mice display impeded adipogenesis. Specifically, Akt1 and Akt2 are required for the induced expression of PPARgamma, the master regulator of adipogenesis, establishing a new essential role for Akt in adipocyte differentiation. Overall, the combined deletion of Akt1 and Akt2 establishes in vivo roles for Akt in cell proliferation, growth, and differentiation. These functions of Akt were uncovered despite the observed lower level of Akt activity mediated by Akt3 in Akt1/Akt2 DKO cells, suggesting that a critical threshold level of Akt activity is required to maintain normal cell proliferation, growth, and differentiation.