Abstract
Physiological polyamines are required in various biological processes. In the current study, we used norspermidine, a structural analog of the natural polyamine spermidine, to investigate polyamine uptake in the model organism Caenorhabditis elegans. Norspermidine was found to have two remarkable effects: it is toxic for the nematode, without affecting its food, Escherichia coli; and it hampers RNA interference. By characterizing a norspermidine-resistant C. elegans mutant strain that has been isolated in a genetic screen, we demonstrate that both effects, as well as the uptake of a fluorescent polyamine-conjugate, depend on the transporter protein CATP-5, a novel P(5B)-type ATPase. To our knowledge, CATP-5 represents the first P(5)-type ATPase that is associated with the plasma membrane, being expressed in the apical membrane of intestinal cells and the excretory cell. Moreover, genetic interaction studies using C. elegans polyamine synthesis mutants indicate that CATP-5 has a function redundant to polyamine synthesis and link reduced polyamine levels to retarded postembryonic development, reduced brood size, shortened life span, and small body size. We suggest that CATP-5 represents a crucial component of the pharmacologically important polyamine transport system, the molecular nature of which has not been identified so far in metazoa.