Lucia Daino

Role of HSP90, CDC37, and CRM1 as modulators of P16INK4A activity in rat liver carcinogenesis and human liver cancer

Current evidence indicates that neoplastic nodules induced in liver of Brown Norway (BN) rats genetically resistant to hepatocarcinogenesis are not prone to evolve into hepatocellular carcinoma. We show that BN rats subjected to diethylnitrosamine/2‐acetylaminofluorene/partial hepatectomy treatment with a “resistant hepatocyte” protocol displayed higher number of glutathione‐S‐transferase 7‐7(+) hepatocytes when compared with susceptible Fisher 344 (F344) rats, both during and at the end of 2‐acetylaminofluorene treatment. However, DNA synthesis declined in BN but not F344 rats after completion of reparative growth. Upregulation of p16INK4A, Hsp90, and Cdc37 genes; an increase in Cdc37‐Cdk4 complexes; and a decrease in p16INK4A‐Cdk4 complexes occurred in preneoplastic liver, nodules, and hepatocellular carcinoma of F344 rats. These parameters did not change significantly in BN rats. E2f4 was equally expressed in the lesions of both strains, but Crm1 expression and levels of E2f4‐Crm1 complex were higher in F344 rats. Marked upregulation of P16INK4A was associated with moderate overexpression of HSP90, CDC37, E2F4, and CRM1 in human hepatocellular carcinomas with a better prognosis. In contrast, strong induction of HSP90, CDC37, and E2F4 was paralleled by P16INK4A downregulation and high levels of HSP90‐CDK4 and CDC37‐CDK4 complexes in hepatocellular carcinomas with poorer prognosis. CDC37 downregulation by small interfering RNA inhibited in vitro growth of HepG2 cells. In conclusion, our findings underline the role of Hsp90/Cdc37 and E2f4/Crm1 systems in the acquisition of a susceptible or resistant carcinogenic phenotype. The results also suggest that protection by CDC37 and CRM1 against growth restraint by P16INK4A influences the prognosis of human hepatocellular carcinoma.(HEPATOLOGY 2005;42:1310–1319.)

Correlation between S-adenosyl-L-methionine content and production of c-myc, c-Ha-ras, and c-Ki-ras mRNA transcripts in the early stages of rat liver carcinogenesis

gamma-Glutamyltranspeptidase (GGT)-positive and glutathione S-transferase (placental-GST-P) positive foci were induced in male Wistar rats by initiation with diethylnitrosamine (DENA), followed by selection and phenobarbital (PB). GGT- and GST-P-positive foci occupied 20-46% and 27-68% of liver parenchyma, respectively, 5-9 weeks after initiation. A high DNA synthesis was found in GGT-positive foci. Decrease in S-adenosyl-L-methionine (SAM) level and SAM/S-adenosylhomocysteine (SAH) ratio, and overall DNA hypomethylation occurred in the liver during the development of enzyme altered foci (EAF). These parameters underwent very small and transient changes in the liver of uninitiated rats at the 5th week, when EAF occupied 0.7-1.4% of the liver. At the 9th week, high RNA transcripts of c-myc, c-Ha-ras, and c-Ki-ras were found in the liver of initiated rats, but not in that of uninitiated rats. Immunohistochemical evaluation of c-myc gene product showed overexpression in GST-P-positive cells. SAM treatment of initiated rats caused inhibition of EAF growth, recovery of SAM/SAH ratio and DNA methylation, and decrease in protooncogene expression proportional to the dose and length of treatment. Liver SAM/SAH ratio was positively correlated with DNA methylation, and negatively correlated with transcript levels of the three protooncogenes. Thus, decrease in SAM/SAH ratio and DNA hypomethylation are early features of hepatocarcinogenesis promotion in rats fed a diet containing adequate lipotrope amounts, paralleled by overexpression of growth-related genes and rapid growth. Re-establishment of a physiologic SAM level makes it possible to inhibit protooncogene expression and EAF growth and to prevent late liver lesion development.

Inhibition by Dehydroepiandrosterone of Liver Preneoplastic Foci Formation in Rats After Initiation-Selection in Experimental Carcinogenesis

The effect of dehydroepiandrosterone (DHEA) on the development of liver preneoplastic foci was evaluated. The experimental protocol used initiation by diethylnitrosamine (DENA), followed by selective growth induced by partial hepatectomy (PH), in rats fed an N-acetylamino-fluorene (AAF)-containing diet, and followed by a standard diet with or without 0.05% phenobarbital (PB). DHEA (0.6%) was administered in the diet for 4 or 7 weeks after DENA injection (treatments A and B) or for 3 weeks after the end of AAF feeding (treatment C). On the 7th week after DENA injection, DHEA treatments A and C caused slight decrease of body weight and 40–60% increase in liver weight and cell size; number of nuclei per g of liver was not changed. The dietary treatment also caused a marked decrease of liver glucose-6-phosphate dehydrogenase (G6PD) activity and of the percentage of the γ-glutamyltranspeptidase (GGT)-positive liver. PB increased G6PD activity and GGT-positive liver. This effect was oblated by DHEA treatments A and C. On the 7th week, the labeling index (LI) was low in surrounding liver, and high in GGT-positive foci. PB had an enhancing effect, while DHEA treatments A and C were inhibitory. G6PD was low at the end of DHEA treatment B, but it returned to normal values 4 weeks after the end of this treatment. At this time no effect of DHEA treatment B was observed on the extent of GGT-positive liver and LI. The observation that an inhibition of GGT-positive liver formation occurs when DENA is given at the end of the AAF/PH treatment in DENA initiated rats could indicate that the DHEA antipromoting effect depends more on growth inhibition than on interference with carcinogen metabolism.

Correlation of c‐myc overexpression and amplification with progression of preneoplastic liver lesions to malignancy in the poorly susceptible wistar rat strain

Persistent liver nodules (Pns) and hepatocellular carcinomas (HCCs) induced in F344 rats by the resistant hepatocyte (RH) model exhibit c‐myc overexpression and amplification. The role of these changes in progression of PN was investigated in nodules with different propensities to evolve to HCC in resistant Wistar rats and, for comparison, in susceptible F344 rats. Initiation of rats with diethylnitrosamine was followed by selection with 2‐acetylaminofluorene (AAF) plus partial hepatectomy (RH groups). Two additional Wistar rat groups received a second AAF treatment without (RH+AAF) and with a necrogenic dose of Ccl4 (RH+AAF/CCl4) 15 d after selection. The number to liver ratio and volume of glutathione‐S‐transferase placental form–positive lesions were lower in the Wistar than the F344 RH groups 9 and 32 wk after initiation and increased after a second AAF cycle treatment with and without Ccl4. DNA synthesis in glutathione‐S‐transferase placental form–positive lesions was low in Wistar RH group at 9 wk and was stimulated by additional AAF treatments. HCCs developed at 57–60 wk in F344 RH, Wistar RH+AAF, and RH+AAF/CCl4 rats. Tumor incidence and multiplicity were lower in RH+AAF rats than in RH+AAF/CCl4 and F344 rats. At 32 wk, PN exhibited c‐myc overexpression that increased from RH to RH+AAF rats and to RH+AAF/CCl4 Wistar rats. This was associated with c‐myc amplification in Wistar RH+AAF/CCl4 rats. These results showed correlation of c‐myc overexpression and amplification with nodule propensity to progress to HCC in poorly susceptible Wistar rats and suggested a possible genetic mechanism for susceptibility to hepatocarcinogenesis. The experimental system used in this work may be a valuable tool for studies on molecular mechanisms underlying liver growth and tumorigenesis supported by c‐myc overexpression. Mol. Carcinog. 25:21–29, 1999.

c-myc amplification in pre-malignant and malignant lesions induced in rat liver by the resistant hepatocyte model

We have investigated by restriction fragment analysis genomic abnormalities involving the c‐myc gene in DNA isolated from adenomas and hepatocellular carcinomas (HCCs). Adenomas and HCCs were induced by the “resistant hepatocyte” protocol in diethylnitrosamine‐initiated male F344 rats. Southern‐blot analysis of EcoRI‐restricted DNA from normal liver, early and late adenomas, 12 weeks (EAs) and 30 weeks (LAs) after initiation, and HCCs, showed 2 bands of 18 and 3.2 kb hybridizing with c‐myc, in all tissues. c‐myc amplification occurred in almost all HCCs, and in the majority of EAs and LAs. These results were confirmed by dilution analysis. c‐myc amplification was also seen in adenomas and HCCs by Southern analysis with HindIII‐restricted DNA, and in HCCs by differential PCR. c‐myc mRNA increase occurred in all adenomas and HCCs, but it was higher in the lesions showing gene amplification. Moreover, a 13‐kb DNA extraband, hybridizing with c‐myc, was found in the HindIII‐restricted DNA from HCCs, but not in normal liver and adenomas, and a 7.1‐kb extra band was present in EcoRI‐digested DNA from one LA. EcoRI‐restricted DNA from some adenomas exhibited a decrease in intensity of the 18‐kb fragment, and an increase in intensity of the 3.2‐kb fragment. No alteration in banding pattern occurred in the β‐actin gene in adenomas. These results provide evidence of amplification and some other rearrangements involving the c‐myc gene, in pre‐malignant and malignant liver lesions, induced by the RH protocol, and suggest a role of c‐myc rearrangement in the progression of adenomas to malignancy.

Activation of v‐Myb avian myeloblastosis viral oncogene homolog‐like2 (MYBL2)‐LIN9 complex contributes to human hepatocarcinogenesis and identifies a subset of hepatocellular carcinoma with mutant p53

Up‐regulation of the v‐Myb avian myeloblastosis viral oncogene homolog‐like2 B‐Myb (MYBL2) gene occurs in human hepatocellular carcinoma (HCC) and is associated with faster progression of rodent hepatocarcinogenesis. We evaluated, in distinct human HCC prognostic subtypes (as defined by patient survival length), activation of MYBL2 and MYBL2‐related genes, and relationships of p53 status with MYBL2 activity. Highest total and phosphorylated protein levels of MYBL2, E2F1‐DP1, inactivated retinoblastoma protein (pRB), and cyclin B1 occurred in HCC with poorer outcome (HCCP), compared to HCC with better outcome (HCCB). In HCCP, highest LIN9‐MYBL2 complex (LINC) and lowest inactive LIN9‐p130 complex levels occurred. MYBL2 positively correlated with HCC genomic instability, proliferation, and microvessel density, and negatively with apoptosis. Higher MYBL2/LINC activation in HCC with mutated p53 was in contrast with LINC inactivation in HCC harboring wildtype p53. Small interfering RNA (siRNA)‐mediated MYBL2/LINC silencing reduced proliferation, induced apoptosis, and DNA damage at similar levels in HCC cell lines, irrespective of p53 status. However, association of MYBL2/LINC silencing with doxorubicin‐induced DNA damage caused stronger growth restraint in p53−/− Huh7 and Hep3B cells than in p53+/+ Huh6 and HepG2 cells. Doxorubicin triggered LIN9 dissociation from MYBL2 in p53+/+ cell lines and increased MYBL2‐LIN9 complexes in p53−/− cells. Doxorubicin‐induced MYBL2 dissociation from LIN9 led to p21WAF1 up‐regulation in p53+/+ but not in p53−/− cell lines. Suppression of p53 or p21WAF1 genes abolished DNA damage response, enhanced apoptosis, and inhibited growth in doxorubicin‐treated cells harboring p53+/+. Conclusion: We show that MYBL2 activation is crucial for human HCC progression. In particular, our data indicate that MYBL2‐LIN9 complex integrity contributes to survival of DNA damaged p53−/− cells. Thus, MYBL2 inhibition could represent a valuable adjuvant for treatments against human HCC with mutated p53. (HEPATOLOGY 2011;)

Role of phosphatidylethanolamine methylation in the synthesis of phosphatidylcholine by hepatocytes isolated from choline‐deficient rats

In recent years the transmethylases involved in phosphatidylcholine (PC) synthesis [l] have been the object of a number of studies [2-51. These attempted to elucidate the mechanism of their action as well as their role in several biological processes. However, the importance of transmethylation in the synthesis of the PC moiety of lipoproteins have not yet been established. Previous studies that used labelled S-adenosyl-L-methionine (SAM) as a precursor for PC synthesis via the transmethylase pathway, showed that the latter is enhanced in choline-deficient animals [6-81. In contrast, measurements of the transformation of phosphatidylethanolamine (PE) to PC suggested that phospholipid methylation falls in choline deficiency [9,10]. This decrease could reflect the existence of a limited SAM pool in hepatocytes of choline-deficient animals. In fact, SAM was shown to be a limiting factor for the methylation of phospholipids by rat liver microsomes [5]. Thus, the cellular pool of SAM could be considered as a limiting factor for the synthesis of the PC moiety of lipoproteins in choline-deficiency. As an initial test for this hypothesis we studied the effect of SAM on lipoprotein secretion by hepatocytes isolated in vitro from choline-supplemented (CS) and choline-deficient (CD) rats. The results indicate that the transmethylase pathway may be substituted for the CDP-choline pathway [l l] to supply the PC moiety for lipoproteins when a high cellular SAM pool is maintained by addition of the methyl donor to the incubation medium.

Ras‐driven proliferation and apoptosis signaling during rat liver carcinogenesis is under genetic control

Fast growth and deregulation of G1 and S phases characterize preneoplastic and neoplastic liver lesions of genetically susceptible F344 rats, whereas a G1‐S block in lesions of resistant BN rats explains their low progression capacity. However, signal transduction pathways responsible for the different propensity of lesions from the 2 rat strains to evolve to malignancy remain unknown. Here, we comparatively investigated the role of Ras/Erk pathway inhibitors, involved in growth restraint and cell death, in the acquisition of a phenotype resistant or susceptible to hepatocarcinogenesis. Moderate activation of Ras, Raf‐1 and Mek proteins was paralleled in both rat models by strong induction of Dab2 and Rkip inhibitors. Levels of Dusp1, a specific ERK inhibitor, increased only in BN rat lesions, leading to modest ERK activation, whereas a progressive Dusp1 decline occurred in corresponding lesions from F344 rats and was accompanied by elevated ERK activation. Furthermore, a gradual increase of Rassf1A/Nore1A/Mst1‐driven apoptosis was detected in both rat strains, with highest levels in BN hepatocellular carcinoma (HCC), whereas loss of Dab2IP, a protein implicated in ASK1‐dependent cell death, occurred only in F344 rat HCC, resulting in significantly higher apoptosis in BN than F344 HCC. Taken together, our results indicate a control of the Ras/Erk pathway and the pro‐apoptotic Rassf1A/Nore1A and Dab2IP/Ask1 pathways by HCC susceptibility genes. Dusp1 possesses a prominent role in the acquisition of the phenotype resistant to HCC by BN rats, whereas late activation of RassF1A/Nore1A and Dab2IP/Ask1 axes is implicated in the highest apoptosis characteristic of BN HCC.

The Variations of S-adenosyl-L-methionine Content Modulate Hepatocyte Growth During Phenobarbital Promotion of Diethylnitrosamine-Induced Rat Liver Carcinogenesis*

A decrease in liver S-adenosyl-L-methionine (SAM) content and an increase in ornithine decarboxylase (ODC) activity occurred between the 2nd and the 5th week after starting 2-acetylaminofluorene (AAF) feeding in diethylnitrosamine (DENA)-initiated rats. These rats then received a 0.05% phenobarbital (PB)-containing diet for 18 weeks after the end of AAF feeding. Two weeks after starting AAF, an increase in the hepatocyte labeling index (LI) also occurred in γ-glutamyl-transpeptidase (GGT)-positive foci and surrounding tissue. LI returned to control values in a few days in surrounding tissue, while it remained high for at least 4 weeks in the foci. Analogous changes were observed, but for a shorter period of time, in the rats subjected to partial hepatectomy (PH) plus AAF, in which no GGT-positive foci developed. Twenty-four weeks after starting AAF, 30% of the liver was occupied by visible nodules. ODC activity and LI were high and SAM was low in nodules, but they were near to control values in surrounding liver. SAM administration reconstituted the liver SAM pool, inhibited ODC activity, and prevented visible nodule development. SAM inhibition of ODC activity occurred in vitro only after preincubation with liver homogenate and was enhanced by adenine, an inhibitor of methylthioadenosine (MTA) phosphorylase. MTA addition to the reaction of mixture for ODC determination was inhibitory. The SAM decrease in both liver and nodules was coupled with a decrease of MTA content. SAM administration caused MTA accumulation in the liver. It is suggested that liver SAM content by influencing MTA level, could be a rate-limiting factor for growth and promotion, through a modulation of polyamine synthesis.

Modulatory Mechanisms of Chemical Carcinogenesis: The Role of the NADPH Pool in the Benzo(a)pyrene Activation

Human lymphocytes and human skin fibroblasts isolated in vitro from subjects carrying the Mediterranean variant of glucose-6-phosphate dehydrogenase (G6PD) exhibit an 86-87% decrease of this enzymatic activity. This is coupled with 51% and 61% decreases of the NADPH/NADP+ ratio in the G6PD-deficient human lymphocytes (HL) and human skin fibroblasts (HSF), respectively. There also occurs a 63-67% decrease of the hexose monophosphate shunt (HMS) in the deficient cells. Incubation with 0.1 mM methylene blue stimulates the HMS of normal HL 15-fold and that of deficient lymphocytes only 2.4-fold. These figures are, respectively, 7 and 2.2 in the case of HSF. This behavior of G6PD-deficient HL and HSF is coupled with an increase of the resistance to the cell death induced by benzo(a)pyrene (BP). This effect is mimicked by the incubation of normal HSF with dehydroepiandrosterone (DEA) which strongly inhibits G6PD. In contrast, no differences between normal and deficient HSF occur as a result of the effect of methylnitrosourea (MNU), a carcinogen that does not need metabolic activation. The NADPH-cytochrome c (P450) reductase of G6PD-deficient HL and HSF homogenates becomes lower than that of controls when endogenous G6PD and exogenous glucose 6-phosphate (G6P) and NADP+ are used as a hydrogen donor system in place of NADPH. Normal and G6PD-deficient HL, having comparable BP-hydroxylating activities, in the presence of exogenous G6P, NADP+, and G6PD, were studied to determine the effect of the absence of exogenous G6PD in the reaction system. When exogenous G6PD is omitted, the deficient HL exhibit a BP hydroxylase activity sharply lower than controls. G6PD-deficient HL and HSF are less prone than controls to produce BP water-soluble metabolites. A decrease in the synthesis of BP metabolites, mutagenic for his–Salmonella typhimurium in G6PD-deficient HL, has also been observed. These results suggest that the decreased susceptibility of G6PD-deficient cells and HSF to the toxic effect of BP and that of deficient HSF to its previously observed transforming effect, could depend on a reduced BP metabolism in the deficient cells.