Induction of hepatocyte proliferation and death by modulation of T-Antigen expression

Abstract

Mice expressing SV40 T-Antigen in liver under control of the phosphoenolpyruvate carboxykinase promoter were generated. By altering the carbohydrate content of the diet, TAg expression, the rate of hepatocyte proliferation and apoptosis, and hence hepatocarcinogenesis, could be regulated. Carbohydrate-mediated suppression of TAg resulted in slow hepatic growth that progressed to focal hepatocellular carcinoma (HCC) after a long latency period. In contrast, induction of TAg by feeding mice a low carbohydrate diet resulted in massive hepatomegaly that progressed rapidly to diffuse multifocal HCC. Hepatic TAg expression could be efficiently repressed by switching mice from the low to the high-carbohydrate diet, which if instigated prior to the development of HCC, resulted in rapid regression through a p53-independent reduction in hepatocyte proliferation and an increase in hepatocyte apoptosis. Although liver growth was accompanied by compensatory hepatocyte apoptosis, an apoptotic deficit developed following chronic exposure to high levels of TAg. This was associated with Akt phosphorylation and increased expression of the antiapoptotic molecules bfl-1/A1, TIAP, and A20. Mice were resistant to Fas-induced hepatocellular apoptosis due to severely impaired caspase activation and failed activation of the mitochondrial amplification loop. This model will be useful to investigate oncogene-mediated disruption of the cell cycle and apoptosis, and to determine which processes constitute fixed, or reversible aspects of the tumorigenic process.

Establishment of a Functional Ovine Fetoplacental Artery Endothelial Cell Line with a Prolonged Life Span1

“…Thus, SV40 OFPAE cells must be deprived of serum for at least 48 h (vs. 24 h for untransfected OFPAE cells [6]) to lower the basal levels enough to detect their responses (proliferation and kinase phosphorylation) to FGF2 and VEGF. These hyperactive basal levels are not surprising, since the expression of SV40 T and t antigens abrogates the negative control of the cell cycle processes and elevates the phosphorylation of MAPK3/1 and AKT1 [8][9][10][11].…”

“…The SV40 gene has been widely used to immortalize or greatly extend the life span of many endothelial cell lines with different origins, including those from human cerebromicrovessels [12], the umbilical veins (HUVE) [13,14], and the placental microvasculature [15]. The SV40 exerts its effects primarily by binding and inactivating retinoblastoma (Rb) and p53 tumor suppressor proteins as well as inhibiting protein phosphatase 2 (PPP2, also known as PP2A), thus releasing cell division from any further restrictions [7][8][9][10][11].…”

“…Compared to their parental, untransfected cells, SV40 OFPAE cells have acquired an extended life span. This prolonged life span of SV40 OFPAE cells may be caused largely by the combined actions of SV40 T and t antigens: the T antigen abrogates the function of Rb and p53, while the t antigen suppresses PPP2 activity [8][9][10][11]. To date, it is unclear whether they have attained immortalization.…”

“…One efficient approach to overcome this senescence crisis is to introduce the simian virus 40 (SV40) gene, bearing T and t antigens, into the primary cells [7][8][9][10][11]. The SV40 gene has been widely used to immortalize or greatly extend the life span of many endothelial cell lines with different origins, including those from human cerebromicrovessels [12], the umbilical veins (HUVE) [13,14], and the placental microvasculature [15].…”

Thymic hyperplasia and lung carcinomas in a line of mice transgenic for keratin 5-driven HPV16 E6/E7 oncogenes

“…Although promoters with a wide range of tissue speci®city (Kondoh et al, 1991;Arbeit et al, 1993) were also used, in most cases the expression of the HPV oncogenes has been speci®cally targeted to epithelial cell type Griep et al, 1993;Arbeit et al, 1994;Pan and Griep, 1994;Howes et al, 1994;Auewarakul et al, 1994;Ledent et al, 1995;Comerford et al, 1995;Herber et al, 1996). Expression of HPV 16 E6 and E7 driven by the human keratin 14 (K14) gene promoter in transgenic mice induced squamous carcinoma exclusively in the vagina and cervix of transgenic females following prolonged exposure to sex hormones (Coussens et al, 1996).…”