TUMOR-CELL INVASION OF BASEMENT-MEMBRANE IN-VITRO IS REGULATED BY AMINO-ACIDS

Because most cancer deaths result from disseminated disease, understan ding the regulation of tumor invasion and metastasis is a central them e in tumor cell biology. Interactions between extracellular matrices ( ECM) and cellular microenvironment play a crucial role in this process . We have tested selected amino acids and polyamines for their ability to regulate RL95-2 cell invasion through both intact human amniotic b asement membrane and a novel human ECM (Amgel). Three major systems fo r neutral amino acid transport, systems L, A, and ASC, are operational in these neoplastic cells. Amino acids entering the cell via transpor t system A or N, i. e., (methyl amino)-isobutyrate (MeAIB) or Asn, mar kedly enhanced invasiveness of these human adenocarcinoma cells as mea sured by a standard 72-hr amnion or Amgel invasion assay. Addition of 2-amino-2-norborane carboxylic acid (BCH; 1 mM), a model substrate of the L transport system, caused a significant decrease in invasive acti vity when tested in the Ail?gel assay. Interestingly, Val lowers stead y-state levels of MeAIB uptake and blocks the increase in cell invasio n elicited by MeAIB. At the same time, these amino acids do not influe nce cell proliferation activity. Neither the charged amino acid Lys or Asp (not transported by A/A/L systems) nor the polyamines putrescine, spermidine, or spermine modulate invasiveness under similar experimen tal conditions. Moreover, the observed time-dependent stimulation of s ystem A activity (cellular influx of MeAIB) by substrate depletion is prevented by the addition of actinomycin D (5 mu M) or cycloheximide ( 100 mu M), suggesting the involvement of de novo RNA and protein synth esis events in these processes. MeAIB treatment of tumor cells selecti vely increased the activities of key invasion-associated type IV colla genases/gelatinases. These results indicate that in the absence of def ined regulators (growth factors or hormones), certain amino acids may contribute to the epigenetic control of human tumor cell invasion and, by extension, metastasis. We propose that amino acids, acting via spe cific signaling pathways, modulate phenotypic cell behavior by modulat ing the levels of key regulatory enzymatic proteins.