Prohibitin 1 Regulates the H19-Igf2 Axis and Proliferation in Hepatocytes

Abstract

Edited by Xiao-Fan WangProhibitin 1 (PHB1) is a mitochondrial chaperone that regulates cell growth. Phb1 knock-out mice exhibit liver injury and hepatocellular carcinoma (HCC). Phb1 knock-out livers show induction of tumor growth-associated genes, H19 and insulinlike growth factor 2 (Igf2). These genes are controlled by the imprinting control region (ICR) containing CCCTC-binding transcription factor (CTCF)-binding sites. Because Phb1 knockout mice exhibited induction of H19 and Igf2, we hypothesized that PHB1-mediated regulation of the H19-Igf2 axis might control cell proliferation in normal hepatocytes. H19 and Igf2 were induced (8 -20-fold) in 3-week-old Phb1 knock-out livers, in Phb1 siRNA-treated AML12 hepatocytes (2-fold), and HCC cell lines when compared with control. Phb1 knockdown lowered CTCF protein in AML12 by ϳ30% when compared with control. CTCF overexpression lowered basal H19 and Igf2 expression by 30% and suppressed Phb1 knockdown-mediated induction of these genes. CTCF and PHB1 co-immunoprecipitated and colocalized on the ICR element, and Phb1 knockdown lowered CTCF ICR binding activity. The results suggest that PHB1 and CTCF cooperation may control the H19-Igf2 axis. Human HCC tissues with high levels of H19 and IGF2 exhibited a 40 -50% reduction in PHB1 and CTCF expression and their ICR binding activity. Silencing Phb1 or overexpressing H19 in the mouse HCC cell line, SAMe-D, induced cell growth. Blocking H19 induction prevented Phb1 knockdown-mediated growth, whereas H19 overexpression had the reverse effect. Interestingly H19 silencing induced PHB1 expression. Taken together, our results demonstrate that the H19-Igf2 axis is negatively regulated by CTCF-PHB1 cooperation and that H19 is involved in modulating the growthsuppressive effect of PHB1 in the liver.

The mitochondrial chaperone Prohibitin 1 negatively regulates interleukin-8 in human liver cancers

“…Although PHB1 is best known as a mitochondrial chaperone protein, increasing evidence shows that it has many other important functions, some of which pertain to cancer. Subcellular localization and posttranslational modifications may explain the tumor-regulatory activity of PHB1 in different cell types (14,22). In particular, mitochondrial and membrane-associated PHB1 in some cancer cells (such as cervical, lung, and bladder) have been shown to confer anti-apoptotic effects and tumorigenesis (23)(24)(25).…”

“…S3). This may be part of the explanation why PHB1 appears to act mainly as a tumor suppressor in the liver (12)(13)(14). In the nucleus, PHB1 acts as a transcription co-factor that can either activate (such as p53) or repress (such as E2F1) gene expression (2-4).…”

“…We found that hepatic PHB1 expression is down-regulated at the mRNA level in the majority of human patients with HCC and CCA, and reduced PHB1 expression increases the growth of HCC and CCA cells and inversely correlates with tumor growth in the murine CCA model (13). We have identified two potential mechanisms of PHB1's tumor-suppressive effects in the liver: first by negatively regulating the insulin-like growth factor 2 (IGF2)-H19 axis (14) and second by heterodimerizing with MAX to bind and repress E-box-driven gene expression, such as c-MYC (13). A major goal of this work was to identify other targets of PHB1 that are important in liver tumorigenesis.…”

Efeito da lectina ArtinM na hepatocarcinogênese induzida por Aflatoxina B1

“…A PBT é uma proteína que atua como supressora tumoral por meio da inibição da atividade do fator de transcrição E2F ou do estímulo à atividade de p53, resultando na redução da proliferação celular e na indução de apoptose (WANG et al, 2002;FUSARO et al, 2003;SÁNCHEZ-QUILES et al, 2010;PENG et al, 2015;RAMANI et al, 2016). Neste estudo, verificou-se que as expressões gênica e proteica de PBT no fígado dos animais intoxicados por AFB1 e tratados com ArtinM foram significativamente maiores em comparação aos animais apenas intoxicados por AFB1.…”

“…Além disso, hepatócitos deficientes em PBT apresentaram hiperexpressão de dois genes relacionados com a formação do CHC: H19 e fator de crescimento semelhante à insulina (RAMANI, 2016 (HUI et al, 1998;NIU et al, 2015). A proteína oriunda do gene p27 KIP1 tem sido descrita como um inibidor de CDK crucial para a regulação negativa da progressão através das fases G1/S do ciclo celular no CHC.…”