Mutations in the gene encoding ATP-binding cassette transporter 1 ( ABC1) have been reported in Tangier disease (TD), an autosomal recessive disorder that is characterized by almost complete absence of plasma high-density lipoprotein (HDL), deposition of cholesteryl esters in the reticulo-endothelial system (RES) and aberrant cellular lipid trafficking. We demonstrate here that mice with a targeted inactivation of Abc1 display morphologic abnormalities and perturbations in their lipoprotein metabolism concordant with TD. ABC1 is expressed on the plasma membrane and the Golgi complex, mediates apo-AI associated export of cholesterol and phospholipids from the cell, and is regulated by cholesterol flux. Structural and functional abnormalities in caveolar processing and the trans-Golgi secretory pathway of cells lacking functional ABC1 indicate that lipid export processes involving vesicular budding between the Golgi and the plasma membrane are severely disturbed.

P rimary hepatocellular carcinoma (HCC) is one of the most fatal cancers in humans with rising incidence in many regions around the world.(1) The majority of HCC patients have a background of chronic liver disease, and the presence of liver cirrhosis is the main risk factor for the development of HCC. (2,3)

We have recently shown that the adenovirus type 5 E4orf6 protein interacts with the cellular tumor suppressor protein p53 and blocks p53 transcriptional functions. Here we report that the E4orf6 protein can promote focus formation of primary rodent epithelial cells in cooperation with adenovirus E1A and E1A plus E1B proteins. The E4orf6 protein can also inhibit p53-mediated suppression of E1A plus E1B-19kDa-induced focus formation. Mutant analysis of the E4orf6 protein demonstrates that these activities correlate with the ability of the adenovirus protein to relieve transcriptional repression mediated by the carboxyl-terminal region of p53 in transient transfection assays. We further demonstrate that expression of wild-type E4orf6 correlates with a dramatic reduction of p53 steady-state levels in transformed rat cells. Our data demonstrate that adenovirus type 5 encodes two different proteins, E1B-55kDa and E4orf6, that bind to p53 and contribute to transformation by modulating p53 transcriptional functions.

High malignancy and early metastasis are hallmarks of melanoma. Here, we report that the transcription factor Snail1 inhibits expression of the tumor suppressor CYLD in melanoma. As a direct consequence of CYLD repression, the protooncogene BCL-3 translocates into the nucleus and activates Cyclin D1 and N-cadherin promoters, resulting in proliferation and invasion of melanoma cells. Rescue of CYLD expression in melanoma cells reduced proliferation and invasion in vitro and tumor growth and metastasis in vivo. Analysis of a tissue microarray with primary melanomas from patients revealed an inverse correlation of Snail1 induction and loss of CYLD expression. Importantly, tumor thickness and progression-free and overall survival inversely correlated with CYLD expression. Our data suggest that Snail1-mediated suppression of CYLD plays a key role in melanoma malignancy.