Phorbol esters stimulate the transport of anionic amino acids in cultured human fibroblasts (original) (raw)

The regulation of sodium-dependent transport of anionic amino acids in cultured human fibroblasts

FEBS Letters, 1994

In cultured human fibroblasts the transport of anionic amino acids through the sodium-dependent system Xi, is stimulated rapidly and transiently by phorbol 12,13-dibutyrate. Transport stimulation is consistent with an effect due to the activation of protein kinase C. Bradykinin (1 PM) and PDGF-AA (100 &ml) also stimulate the activity of system Xi,. The bradykinin effect appears to be fully dependent upon PKC activation whereas the stimulation of aspartate transport by PDGF-AA is also due to PKC-independent mechanisms.

The relationship between sodium-dependent transport of anionic amino acids and cell proliferation

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993

The relationship between the transport of anionic amino acids and the proliferative status of the cell population has been studied in NIH-3T3 cells. Proliferative quiescence, verified by determinations of growth-rate quotient and incorporation of thymidine, is associated with a marked increase of the influx of L-aspartate. After 7-10 days of serum starvation, the initial influx of L-aspartate increases by 8-10-times with respect to the transport activity determined in growing cells. The operational properties of the influx of L-aspartate are similar in growing and quiescent cells; in particular, the influx of the anionic amino acid is mostly Na+-dependent and completely suppressed by an excess of L-glutamate and D-aspartate, but not of D-glutamate. These features suggest that, in both cases, aspartate uptake occurs through system XxG. The quiescence-related increase in aspartate transport is gradual, sensitive to the inhibition of protein synthesis and referable to the enhanced maximal capacity of transport system XxG. Restoration of serum concentration in the culture medium of serum-starved cells causes a decrease in aspartate transport that is maximal in correspondence to late G~/S phases. It is concluded that the XXG system for anionic amino-acid uptake is sensitive to the proliferative status of the cell population and that, in particular, its transport activity is stimulated by the establishment of proliferative quiescence.

Amino acid transport systems modulate human tumor cell growth and invasion: A working hypothesis

Medical Hypotheses, 1995

Interactions between the extracellular matrix (ECM) and the neoplastic cells they envelop are thought to play a fundamental role in those cells' ability to invade, one of the key events in the metastatic cascade. Cellular transport of amino acids, in turn, is known to be mediated by functionally distinct membrane transport systems and is modulated by substrate bioavailability in the microenvironment. We postulate that certain advantages enjoyed by a neoplastic cell population over their normal counterparts (for example, increased proliferating capability and invasiveness across ECM barriers) are linked to changes in the cells' differential control of amino acid transport (aaT) via host ECM-tumor cell generated signals. Our studies suggest that active transport of neutral amino acids modulates a cells' functional behavior among phenotypically distinct human transformed cell types, irrespective of whether they are categorized as a sarcoma, melanoma, or carcinoma. We present preliminary laboratory evidence which has lead us to formulate a series of working hypotheses as follows: 1. aaT systems operating in both non-transformed and transformed human cells exhibit differential transport kinetics; 2. adaptive regulation of certain amino acids via cell-specific aaT systems alters a cell's ability to invade human ECM; and 3. aaT induction involves changes both at the cellular and molecular levels. This report, therefore, provides experimental support, and suggests a possible mechanism, to explain how neutral amino acids, acting as nutrient signalling factors (along with other biologic elements) within the cell milieu, have the capability of regulating the phenotypic nature of human neoplastic cells.

Glycine transport by cultured human fibroblasts

Biochemical and Biophysical Research Communications, 1988

The transport of glycine was studied in cultured human fibroblasts. The amino acid entered the cell by Na+-dependent and Na+-independent mechanisms. Na+-independent glycine (0.i mM) transport was less than 10% of total uptake and occurred by a mechanism formally indistinguishable from diffusion. Two distinct routes contributed to Na+-dependent glycine transport. The first route was identified with system A because it was inhibited by MeAIB and underwent adaptive regulation. The second route was identified with system ASC as it was inhibited by L-alanine, but not by MeAIB. Kinetic analysis revealed that the two systems operated glycine transport with the same Km of 1.6 mM, a value unusually high for system ASC.

Pathways of L-glutamic acid transport in cultured human fibroblasts

Journal of Biological Chemistry

The transport of L-glutamic acid has been studied in skin-derived diploid human fibroblasts. Competition analysis in the presence and absence of Na+ and mathematical discrimination by nonlinear regression indicated that L-glutamic acid enters the cell by at least three transport systems: 1) a high affinity Na+-dependent system which has been found to be identical to the previously described system for anionic amino acids (Gazzola, G. C., Dall'Asta, V., Bussolati, O., Makowske, M., and Christensen, H. N. (1981) J. Biol.

Phorbol Esters Rapidly Attenuate Glutamine Uptake and Growth in Human Colon Carcinoma Cells

Journal of Surgical Research, 2000

Background. The amino acid glutamine, while essential for gut epithelial growth, has also been shown to stimulate colon carcinoma proliferation and diminish differentiation. Human colon carcinomas are known to extract and metabolize glutamine at rates severalfold greater than those of normal tissues, but the regulation of this response is unclear. Previously we reported that phorbol esters regulate hepatoma System ASC/B 0-mediated glutamine uptake and cell growth. As human colon carcinoma cells use this same transporter for glutamine uptake, the present studies were undertaken to determine whether similar regulation functions in colon carcinoma. Materials and methods. Human colon carcinoma cell lines (WiDr and HT29) were treated with the protein kinase C (PKC) activator phorbol 12-myristate 13acetate (PMA) and initial-rate transport of glutamine and other nutrients was measured at specific times thereafter. Growth rates were monitored during culture ؎ PMA or an excess of System ASC/B 0 substrates relative to glutamine. Results. PMA treatment induced a rapid inhibition of glutamine uptake rates in WiDr and HT29 cells by 30 and 57%, respectively, after 1 h. Cycloheximide failed to block this response, indicating that the mechanism by which PMA exerts its effects is posttranslational. The inhibition of glutamine uptake by PMA was abrogated by the PKC inhibitor staurosporine, suggesting that this rapid System ASC/B 0 regulation may be mediated by a PKC-dependent pathway. PMA also significantly decreased transport via System y ؉ (arginine) and System A (small zwitterionic amino acids). Chronic phorbol ester treatment inhibited WiDr cell growth, as did attenuation of System B 0-mediated glutamine uptake with other transporter substrates. Conclusions. System ASC/B 0 uptake governs glutamine-dependent growth in colon carcinoma cell lines, and is regulated by a phorbol ester-sensitive pathway that may involve PKC. The results further establish the link between glutamine uptake and colon carcinoma cell growth, a relationship worthy of further investigation with the goal of discovering novel cancer therapeutic targets.