Adenoviral modulation of the tumor-associated system L amino acid transporter, LAT1, alters amino acid transport, cell growth and 4F2/CD98 expressionwith cell-type specific effects in cultured hepatic cells

Altered expression of metabolite transporters is observed frequently in tumor cell lines and primary neoplasms. The extent to which these may to contribute to the growth autonomy associated with cancer is not clear. LAT1 is a major L-type amino acid transporter over-expressed in a variety of cancer types and a light chain component of the CD98 heterodimer. We utilized an adenoviral expression system to modulate the level of LAT1 in a hepatic in vitro model to examine phenotypic changes associated with short-term exogenous and blocked expression. LAT1 levels were increased three fold and resulted in increased L-type amino acid transport as a result of adenoviral expression in murine hepatocytes. The protein was expressed on the cell surface and complexed with the CD98 heavy chain known as 4F2. Surprisingly, levels of the total CD98 protein complex were increased 2.4-fold as a result of adenoviral expression of light chain only, suggesting coordinate regulation. Exogenous overexpression was less effective in normal rat liver cells relative to mouse. LAT1 antisense expression in hepatic tumor cells resulted in a modest though statistically significant decrease in cell number, viability and S-phase cells over a 5-day period relative to controls despite the absence of a significant decrease in L-type transport over this period. These studies are preparatory to in vivo efforts focusing on LAT1/CD98 as a potential therapeutic target.