HNF1α Inactivation Promotes Lipogenesis in Human Hepatocellular Adenoma Independently of SREBP-1 and Carbohydrate-response Element-binding Protein (ChREBP) Activation

Abstract

Biallelic inactivating mutations of the transcription factor 1 gene (TCF1), encoding hepatocyte nuclear factor 1␣ (HNF1␣) were identified in 50% of hepatocellular adenomas (HCA) phenotypically characterized by a striking steatosis. To understand the molecular basis of this aberrant lipid storage, we performed a microarray transcriptome analysis validated by quantitative reverse transcription-PCR, Western blotting, and lipid profiling. In mutated HCA, we showed a repression of gluconeogenesis coordinated with an activation of glycolysis, citrate shuttle, and fatty acid synthesis predicting elevated rates of lipogenesis. Moreover, the strong down-regulation of liver fatty acid-binding protein suggests that impaired fatty acid trafficking may also contribute to the fatty phenotype. In addition, transcriptional profile analysis of the observed deregulated genes in non-HNF1␣-mutated HCA as well as in non-tumor livers allowed us to define a specific signature of the HNF1␣-mutated HCA. In these tumors, lipid composition was dramatically modified according to the transcriptional deregulations identified in the fatty acid synthetic pathway. Surprisingly, lipogenesis activation did not operate through sterol regulatory element-binding protein-1 (SREBP-1) and carbohydrate-response element-binding protein (ChREBP) that were repressed. We conclude that steatosis in HNF1␣-mutated HCA results mainly from an aberrant promotion of lipogenesis that is linked to HNF1␣ inactivation and that is independent of both SREBP-1 and ChREBP activation. Finally, our findings have potential clinical implications since lipogenesis can be efficiently inhibited by targeted therapies. Hepatocyte nuclear factor 1-␣ (HNF1␣)3 is a transcription factor that controls the expression of liver-specific genes, such as ␤-fibrinogen, ␣1-antitrypsin, and albumin (1). Heterozygous germline mutations in the gene encoding HNF1␣ (TCF1 (transcription factor 1)) are responsible for an autosomal dominant form of non-insulin-dependent diabetes mellitus called maturity onset diabetes of the young type 3 (MODY3), in which subjects usually develop hyperglycemia before 25 years of age (2). More recently, we identified HNF1␣ as a tumor suppressor gene involved in human liver tumorigenesis since we found biallelic inactivating mutations of this gene in 50% of hepatocellular adenomas (HCA) and in rare cases of well differentiated hepatocellular carcinomas developed in the absence of cirrhosis (3). HCA are rare benign primary liver tumors closely related to oral contraceptive intake (4).Recently, in a comprehensive analysis of genotype-phenotype correlations in a large series of 96 HCA, we showed that HNF1␣ mutations define a homogeneous group of tumors phenotypically characterized by the recurrent presence of a marked steatosis (5). To get insight into the underlying molecular mechanisms that drive the fatty phenotype in human HNF1␣-mutated HCA, we performed a transcriptome analysis using cDNA and Affymetrix microarrays. Gene expression profiles were compared between non-t...

Molecular pathogenesis of focal nodular hyperplasia and hepatocellular adenoma

“…We also found a silencing of L-FABP, which encodes liver fatty acid binding protein 1, suggesting that impaired fatty acid trafficking may also contribute to the fatty phenotype. We showed that absence of L-FABP staining in HCA was specific to HNF1α inactivation among the different benign liver tumor subtypes (82,87). Together this indicates that steatosis, frequently observed in HCA, may contribute to tumorigenesis, and this occurs through a constant and specific mechanism in the HNF1α inactivated tumor subtype.…”

“…Furthermore, we identified a repression of gluconeogenesis coordinated with an activation of glycolysis, citrate shuttle and fatty acid synthesis, which predicted elevated rates of lipogenesis in HCA tumors harboring mutations in HNF1α (87). In these tumors, lipid composition was dramatically modified and, surprisingly, lipogenesis activation did not operate through SREBP-1 and ChREBP, both of which instead were repressed.…”

Hepatocellular adenomas: Magnetic resonance imaging features as a function of molecular pathological classification

“…3,4 This steatosis results from the activation of lipogenesis. 5 Steatosis is also observed in other subtypes of HCA, but less frequently and to a lesser degree. Thus, no lesion without HNF-1␣ inactivation shows such a diffuse distribution of fat, although foci of steatosis may be observed in inflammatory HCA.…”

“…5 Liver fatty acid binding protein (L-FABP), which encodes L-FABP 1, has also been shown to be silenced in these tumors, suggesting that impaired fatty acid trafficking may also contribute to the fatty phenotype of HNF-1␣-inactivated HCA.…”

Hepatic adenomas with synchronous or metachronous fibrolamellar carcinomas: both are characterized by LFABP loss

“…LFABP is a downstream target of HNF1-α 13 and bialellic loss of HNF1-α is associated with loss of LFABP expression, an observation that forms the foundation for using LFABP immunohistochemistry as a diagnostic tool. 14 It is unknown how the loss of the tumor suppressor HNF1-α contributes to neoplasia, but biallelic loss of HNF1-α can lead to activation of glycolysis and lipogenesis, 15,16 as well as upregulation of ERBB2 and mTOR. Other possible targets include upregulation of cyclin D1 to promote cell division and upregulation of PDGFA and PDGFB, facilitating angiogenesis.…”