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Regulation of polyamine transport by polyamines and polyamine analogs
Author(s) -
Kramer D. L.,
Miller J. T.,
Bergeron R. J.,
Khomutov R.,
Khomutov A.,
Porter C. W.
Publication year - 1993
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.1041550222
Subject(s) - polyamine , spermine , putrescine , spermidine , intracellular , biochemistry , chemistry , l1210 cells , stimulation , biophysics , biology , enzyme , in vitro , cytotoxicity , endocrinology
Regulation of polyamine transport in murine L1210 leukemia cells was characterized in order to better understand its relationship to specific intracellular polyamines and their analogs and to quantitate the sensitivity by which it is controlled. Up‐regulation of polyamine uptake was evaluated following a 48‐hr treatment with a combination of biosynthetic enzyme inhibitors to deplete intracellular polyamine pools. The latter declined gradually over 48 hr and was accompanied by a steady increase in spermidine (SPD) and spermine (SPM) transport as indicated by rises in V max to levels ∼4.5 times higher than control values. Restoration of individual polyamine pools during a 6‐hr period following inhibitor treatment revealed that SPD and SPM uptake could not be selectively affected by specific pool changes. The effectiveness of individual polyamines in reversing inhibitor‐induced stimulation of uptake was as follows: putrescine < SPD < SPM = the SPM analog, N 1 , N 12 ‐bis(ethyl)spermine (BESPM). In contrast to stimulation of transport, down‐regulation by exogenous polyamines or analogs occurred rapidly and in response to subtle increases in intracellular pools. Following a 1‐hr exposure to 10 μM BESPM, V max values for SPD and SPM fell by 70%, whereas the analog pool increased to only 400–500 pmol/10 6 cells—about 15–20% of the total polyamine pool (∼2.8 nmol/10 6 cells). SPM produced nearly identical regulatory effects on transport kinetics. Both BESPM and SPM were even more effective at down‐regulating transport that had been previously stimulated four to fivefold by polyamine depletion achieved with enzyme inhibitors. A dose response with BESPM at 48 hr revealed a biphasic effect on uptake whereby concentrations of analog < 3 μM produced an increase in SPD and SPM V max values, whereas concentrations 3 μM and higher produced a marked suppression of these values. Cells treated with 3 μM BESPM for 2 hr and placed in analog‐free medium recovered transport capability in only 3 hr. Thus, whereas stimulation of polyamine transport is a relatively insensitive and slowly responsive process that tends to parallel polyamine depletion, down‐regulation of polyamine transport by exogenous polyamines and analogs and its reversal are rapidly responsive events that correlate with relatively small (i.e., 15–20%) changes in intracellular polyamine pools.