Inhibition of growth of proline-requiring Chinese hamster ovary cells (CHO-K1) resulting from antagonism by a system amino acids

Abstract

CHO‐K1 requires proline for growth. Two proline‐independent revertants were isolated—K1‐J and K1‐6. CHO‐K1 pro⁻ is much more sensitive than the pro⁺ cell lines to inhibition of growth by addition to the medium of amino acids and amino acid analogues that are transported through the A system. In contrast, pro⁺ cells are as sensitive as, or in some cases slightly more sensitive than, pro⁻ cells to glycine, basic amino acids, and to amino acids that are mainly transported by the L system. The A system analogue α(methylamino) isobutyric acid (MAIB) in low concentrations reacts competitively with proline to regulate the growth of pro⁻ cells, yielding a K_i for MAIB of 0.56 mM. CHO‐K1 and K1‐6 transport proline at the same initial rate and are equally sensitive to the inhibition of proline transport by alanine. Alanine and MAIB inhibit proline transport strongly and similarly in CHO‐K1. Thus although these compounds inhibit the transport of proline by both cell types to the same extent, pro⁺ cells are immune to the effect of this starvation since they are able to synthesize their own proline. We also describe a secondary inhibition caused by high A system amino acid concentrations that affects both pro⁻ and pro⁺ cells.