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Influence of proliferative rates and a system substrate availability on proline transport in primary cell cultures of the R3230AC mammary tumor
Author(s) -
Gay Roger J.,
Hilf Russell
Publication year - 1980
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041050212
Subject(s) - proline , amino acid , cycloheximide , glycine , biochemistry , alanine , serine , phenylalanine , chemistry , biology , protein biosynthesis , enzyme
Abstract Regulation of A system amino acid transport was studied in primary cultures of the R3230AC mammary adenocarcinoma. Higher rates of carrier‐mediated Na + ‐dependent proline transport, v c , was decreased and was attributed to a two‐fold decrease in Vmax and a two‐fold increase in Km. When compared to cells grown in standard media (Eagle's minimal essential medium, MEM), cells grown in media supplemented with A system substrates (alanine, serine, glycine, and proline) demonstrated adaptive decreases in proline transport; the decrease was due to two‐fold reduction in Vmax, with no change in Km for proline. Even in the presence of preferred substrates for the A system, a density‐dependent decrease in proline transport was manifested. Both fast‐ and slow‐growing cultures maintained in MEM exhibited rapid increases in proline transport when switched to buffers devoid of amino acids; two‐fold increases in Vmax were seen within 4 hr, but Km was unchanged. This starvation‐induced adaptation was completely prevented by inclusion in the buffer of 10 mM proline, 0.1 mM ‐(methylamino)‐isobutyric acid (MetAIB) or 10 mM serine, whereas inclusion of the poorer A system substrate, phenylalanine (10 mM), had no effect. The effects of MetAIB to prevent starvation‐induced increases in proline transport were dose‐related, rapid, and reversible. Amino acid starvation‐induced increases in proline transport were partially blocked by cycloheximide or actinomycin D. Data were obtained demonstrating a temporal relationship between increasing intracellular [proline] and decreasing v c for proline uptake. In addition, efflux of proline from preloaded cells preceded the increase in initial rates of proline entry. Taken together, we concluded that: (1) A system transport in primary cultures of this mammary adenocarcinoma is regulated by cell density as well as by availability of A system substrates, but these two types of regulation are kinetically distinct; and (2) starvation‐induced enhancement of proline transport appears to be due to release from transinhibition, but may also involve a derepression‐repression type of mechanism.