Cell density and amino acid transport in 3T3, SV3T3, and SV3T3 revertant cells

Abstract

The transport of selected neutral and cationic amino acids has been studied in Balb/c 3T3, SV3T3, and SV3T3 revertant cell lines. After properly timed preincubations to control the size of internal amino acid pools, the activity of systems A, ASC, L, and Ly+ has been discriminated by measurements of amino acid uptake (initial entry rate) in the presence and absence of sodium and of transport-specific model substrates. L-Proline, 2-aminoisobutyric acid, and glycine were primarily taken up by system A; L-alanine and L-serine by system ASC; L-phenylalanine by system L; and L-lysine by system Ly+ in SV3T3 cells. L-Proline and L-serine were also preferential substrates of systems A and ASC, respectively, in 3T3 and SV3T3 revertant cells. Transport activity of the Na+-dependent systems A and ASC decreased markedly with the increase of cell density, whereas the activity of the Na+-independent systems L and Ly+ remained substantially unchanged. The density-dependent change in activity of system A occurred through a mechanism affecting transport maximum (Vmax) rather than substrate concentration for half-maximal velocity (Km). Transport activity of systems A and ASC was several-fold higher in transformed SV3T3 cells than in 3T3 parental cells at all the culture densities that could be compared. In SV3T3 revertant cells, transport activity by these systems remained substantially similar to that observed in transformed SV3T3 cells. The results presented here add cell density as a regulatory factor of the activity of systems A and ASC, and show that this control mechanism of amino acid transport is maintained in SV40 virus-transformed 3T3 cells that have lost density-dependent inhibition of growth, as well as in SV3T3 revertant cells that have resumed it.

[14C]Fluciclovine (alias anti-[14C]FACBC) uptake and ASCT2 expression in castration-resistant prostate cancer cells

“…AAT expression is also related to the cancer microenvironment in interesting ways. Intratumoral cell density generally increases with tumor progression, and the transport activity of system ASC, but not of system L, decreases with increasing cell density [38]. We recently demonstrated that [ 18 F]fluciclovine accumulation is positively correlated with cell density in a rat glioma model [39].…”

Different HSP70 expression and cell survival during adaptive responses of 3T3 and transformed 3T3 cells to osmotic stress

“…The induced synthesis of stress proteins by the cells under these conditions has been monitored in terms of the presence of mRNA for HSP70, the pattern of polypeptides synthesised, and the accumulation of HSP70 detectable by monoclonal antibodies. (Borghetti et al, 1980). These cells were routinely kept in culture for up to 2 months and discarded; then fresh cultures were started again from frozen stocks.…”

Localisation of Alanine uptake by cultured renal epithelial cells (LLC‐PK1) to the basolateral membrane

“…A similar decrease has been reported by Lever (1982) when measuring a-aminoisobutyric acid transport. This behaviour is reminiscent of that described in other cells in culture (Guidotti et al, 1978;Borghetti et al, 1980) where a marked decrease in amino acid transport activity was observed as cell density increased. This phenomenon has been interpreted in terms of the coordinated regulation of cell growth, supporting the view that nutrient uptake might play an important role in the regulation of cell growth.…”

“…At least two explanations could account for the uneven distribution of alanine uptake observed here. The first one is based on the observation by Borghetti et al (1980) showing that the activity of system A is modulated so that it is low when high cell density is attained by 3T3Balb C fibroblasts in culture. A similar observation has been reported by Boerner and Saier (1982) for MDCK cells; this is an epithelial cell line derived from canine kidney that retains several characteristics of distal tubular epithelium.…”