Prohibitin 1 suppresses liver cancer tumorigenesis in mice and human hepatocellular and cholangiocarcinoma cells

Abstract

Prohibitin 1 (PHB1) is best known as a mitochondrial chaperone and its role in cancer is conflicting. Mice lacking methionine adenosyltransferase α 1 (MATα1) have lower PHB1 expression and we reported c-MYC interacts directly with both proteins. Furthermore, c-MYC and MATα1 expert opposing effects on liver cancer growth, prompting us to examine the interplay between PHB1, MATα1 and c-MYC and PHB1's role in liver tumorigenesis. We found PHB1 is highly expressed in normal hepatocytes and bile duct epithelial cells and down-regulated in most human hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). In HCC and CCA cells, PHB1's expression correlate inversely with growth. PHB1 and MAT1A positively regulate each other's expression, whereas PHB1 negatively regulates the expression of c-MYC, MAFG and c-MAF. Both PHB1 and MATα1 heterodimerize with MAX, bind to the E-box element and repress E-box promoter activity. PHB1 promoter contains a repressive E-box element, is occupied mainly by MAX, MNT and MATα1 in nonmalignant cholangiocytes and noncancerous tissues that switched to c-MYC, c-MAF and MAFG in cancer cells and human HCC/CCA. All 8-month old liver-specific Phb1 knockout mice developed HCC and one developed CCA. 5-month old Phb1 heterozygotes but not Phb1 flox mice developed aberrant bile duct proliferation and one developed CCA 3.5 months after left and median bile duct ligation (LMBDL). Phb1 heterozygotes had a more profound fall in the expression of GSH synthetic enzymes and higher hepatic oxidative stress following LMBDL. Conclusion We have identified PHB1, down-regulated in most human HCC and CCA, heterodimerizes with MAX to repress the E-box. PHB1 positively regulates MAT1A while suppressing c-MYC, MAFG and c-MAF expression. In mice, reduced PHB1 expression predisposes to the development of cholestasis-induced CCA.

Methionine Adenosyltransferase α1 Is Targeted to the Mitochondrial Matrix and Interacts with Cytochrome P450 2E1 to Lower Its Expression

“…More recently, our study and others have shown that MATα1 can target the nuclear compartment where it can regulate gene expression by epigenetic mechanisms . In addition, we recently showed that MATα1 interacts directly with MAX and c‐MYC and negatively regulates E‐box‐driven reporter activity . This prompted us to investigate the MATα1 interactome, which revealed the unexpected high number of mitochondrial proteins, including CYP2E1 (Supporting Table ).…”

“…(26)(27)(28) In addition, we recently showed that MATα1 interacts directly with MAX and c-MYC and negatively regulates E-box-driven reporter activity. (19) This prompted us to investigate the MATα1 interactome, which revealed the unexpected high number of mitochondrial proteins, FIg. 6.…”

“…We recently showed that MATα1 interacts with proteins such as c‐MYC and MAX (MYC‐associated factor x) to modulate E‐box‐dependent gene expression . The aims of this work were to further define what proteins could interact with MATα1 and to explore how MATα1 regulates CYP2E1 expression and mitochondrial function.…”

“…(9,10) We recently showed that MATα1 interacts with proteins such as c-MYC and MAX (MYC-associated factor x) to modulate E-box-dependent gene expression. (18,19) The aims of this work were to further define what proteins could interact with MATα1 and to explore how MATα1 regulates CYP2E1 expression and mitochondrial function. Here, we revealed the finding that MATα1 is localized to the mitochondrial matrix where it interacts with CYP2E1 to influence mitochondrial membrane potential and generation of ROS.…”

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

“…Our group reported that hepatic PHB1 expression is reduced during chronic cholestatic injury in both experimental murine models and in humans (10,11). We also reported that liverspecific Phb1 knockout mice develop hepatocellular carcinoma (HCC) 3 (12) and that Phb1 heterozygotes are predisposed to cholestasis-associated cholangiocarcinoma (CCA) (13). 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).…”