Hepatocellular carcinoma development induced by conditional β‐catenin activation in Lkb1^+/− mice

Abstract

The development of hepatocellular carcinomas (HCC) appears to be a multistep process that takes several decades in humans. However, the identities of specific gene alterations and their contribution to HCC pathogenesis remain poorly understood. We previously reported that Lkb1 +/--mice spontaneously develop multiple hepatic nodular foci (NdFc) followed by HCC, and that the conditional activation of b-catenin in Catnb lox(ex3) mouse livers alone does not cause tumor formation. We show here that the conditional activation of b-catenin accelerates HCC development in Catnb +/lox(ex3) Lkb1+/--compound mutant mice, affecting displastic hepatocytes in NdFc that suffered LOH at the Lkb1 locus. We further show that b-catnin activation provides HCC with a growth advantage as well as transplantability. These results suggest that the loss of Lkb1 contributes to the formation of dysplastic NdFc, and that Wnt signaling activation is involved in ensuing progression toward HCC. A combination of these sequential changes can be a practical model for a subset of human HCC. (Cancer Sci 2009; 100: 2046-2053 P eutz-Jeghers syndrome (PJS) is an autosomal dominant disease characterized by gastrointestinal hamartoma and mucocutaneous pigmentation as well as the increased risk of cancer.(1,2) The positional cloning studies on chromosome 19p13.3 identified mutations in LKB1 responsible for PJS. (3,4) LKB1 is a serine ⁄ threonine kinase that phosphorylates and activates 14 kinases, including AMP-activated protein kinase (AMPK) and microtubule-associated protein ⁄ microtubule affinity-regulating kinases (MARK).(5) Recent studies have revealed that LKB1 mediates energy-dependent suppression of the mammalian target of rapamycin (mTOR) pathway via AMPK, (6) and that LKB1 suppresses tubulin polymerization by activating MARK-microtubule-associated protein signaling. (7) We previously reported that Lkb1 + ⁄ ) mice develop gastrointestinal hamartomas that have similar histopathology to those in human PJS. (8) In addition, they developed multiple small nodular foci (NdFc) in the liver after 30 weeks of age, and HCC after 40 weeks of age.(9) NdFc consist of dysplastic and proliferative hepatocytes, suggesting that HCC in Lkb1 + ⁄ ) mice originate from these lesions.(9) LKB1 mutations have been identified not only in PJS patients but also in sporadic cancers.(10) Although the liver malignancy in PJS patients has been rarely reported, LKB1 is implicated in the pathogenesis of human HCC. A HCC cell line (BEL9204) and an immortalized hepatocyte line (TPH1) were found to bear homozygous deletions of the LKB1 gene, (11) and 1 of the 80 primary HCC examined had a point mutation in the LKB1 kinase domain.(12) These results suggest that LKB1 deficiency may underlie a subset of human HCC.Wnt signaling activation is a frequent change in HCC as well as in other cancers.(13) Upon activation, the adenomatous polyposis coli (APC)-axin-glycogen synthase kinase 3b (GSK3b) complex is unable to phosphorylate b-catenin, which results in the stabilization of b-catenin ...

Molecular oncogenesis of craniopharyngioma: current and future strategies for the development of targeted therapies

“…Mutations in the b-catenin gene (CTNNB1) on chromosome 3 and aberrations in b-catenin expression have been well documented in multiple cancers, including colorectal 3,4,7,56,70,80 and hepatocellular 25,52,58 carcinomas, which prompted early studies in other solid tumors. CTNNB1 mutations were subsequently found in the Wnt subtype of medulloblastomas 42 and adamantinomatous craniopharyngiomas, 16,21,47,66,78 suggesting that, in addition to being clinically and histopathologically distinct, these subtypes also have distinct genetic origins.…”

Decreased Expression of LKB1 Correlates with Poor Prognosis in Hepatocellular Carcinoma Patients Undergoing Hepatectomy

“…LKB1 is central in regulating cellular metabolism and cell growth by integrating information which included the oxygen status,energy, the presence of growth factors and nutrient availability.Furthurmore, many researches showed frequent LKB1 allelic loss in various human cancers, including hepatocellular carcinoma (HCC), non-small cell lung carcinomas, cervical, breast carcinomas, pancreatic carcinoma and epithelial carcinoma (Avizienyte al., 1999;Shen et al, 2002;Kim al., 2007;Gao al., 2011;Herrmann al., 2011). Animal experiments showed that the loss of LKB1 gene attributes to hepatocarcinogenesis (Miyoshi al., 2009). In breast cancer cells study showed overexpression of LKB1 protein can result in growth inhibition of breast tumor cells and less expression of LKB1 protein contribute to tumor cell cycle progression (Shen et al, 2002;Zhuang al., 2006).…”

LKB1 Suppresses p21-activated Kinase-1 (PAK1) by Phosphorylation of Thr109 in the p21-binding Domain

“…In addition, we and others (7)(8)(9) have previously shown that the heterozygous Lkb1 mutations in mice cause gastrointestinal hamartomas after 20 weeks of age and cause hepatocellular carcinomas (HCCs) 2 after 50 weeks (10). Notably, the Lkb1 gene in all HCC and hepatic precancerous lesions shows loss of heterozygosity (10,11). These phenotypes in Lkb1(ϩ/Ϫ) mice further indicate that LKB1 is a tumor suppressor gene.…”

“…Lkb1(ϩ/Ϫ) mice develop HCC after 50 weeks of age and that HCCs and nodular foci of Lkb1(ϩ/Ϫ) liver show loss of the Lkb1 heterozygosity (10,11). To test the involvement of LKB1 in PAK1-mediated signaling in vivo, we next determined the level of phosphorylated form of PAK1 in HCCs of Lkb1(ϩ/Ϫ) mice, using two different types of phospho-specific PAK1 antibodies that recognized the active form of PAK1.…”