@article{0d3eb9f3727e464c9bcf6a6324c8c341,
title = "Apparent increases in phospholipid degradation and turnover during combined treatment with protein synthesis inhibitors and adrenocorticotropin",
abstract = "Inhibitors of protein synthesis, cycloheximide and puromycin, blocked ACTH (adrenocorticotropin)-induced increases in phospholipid mass, including phosphatidylinositol, but paradoxically increase 32P-labelling (but not [3H]glycerol-labelling) therein. Cycloheximide also provoked an initial rapid decrease in 32P-prelabelled phospholipids, followed by an increase in [32P]Pi incorporation. These effects of cycloheximide and puromycin occurred in ACTH-treated (but not in control) cells. It appears that inhibition of protein synthesis during ACTH action provokes an increase in phospholipid degradation, followed by partial resynthesis of the phospholipid head groups.",
keywords = "(Rat adrenal cell), Adrenocorticotropin, Cycloheximide, Phosphatidylinositol, Phospholipid turnover, Puromycin",
author = "Farese, {Robert V.} and Sabir, {Mohammad A.} and Davis, {John S.}",
note = "Funding Information: From the above results, it seems likely that there is generalized increase in phospholipid degradation and turnover during concomitant treatment with cycloheximide (or puromycin)a nd ACTH. Thus, at least part of the inhibition of ACTH effects on phospholipid metabolism by cycloheximide may be due to enhanced phospholipid degradation. Since [ 32P]Pi incorporation and phospholipid mass change oppositely, it is possible that a nonspecific phospholipase C is involved, resulting in phospholipid degradation and enhanced generation of diacylglycerol, and a subsequent increase in 32P O, incorporation into phosphatidic acid and other phospholipids (note: actual phosphatidic acid mass, however, may also decrease - cf. Refs. l-6 - through enhanced degradation or decreased synthesis). In accordance, we have reported [7] that cycloheximide does not inhibit the ACTH-induced increase in adrenal diacylglycerol formation. The latter, however, may also reflect a partial inhibition of diacylglycerol kinase activity by cycloheximide [7]. Although the relationship between the presently observed increase in phospholipid degradation and the previously observed inhibition of diacylglycerol kinase is not presently clear, it is possible that phospholipase-derived degradation products could have an inhibitory effect on membrane-bound enzymes, such as diacylglycerol kinase. It may be questioned whether the increased level of “P-1abelling of phospholipids (relative to the decreasei n mass) during the combined action of cycloheximide (or puromycin) and ACTH reflected an effect primarily of cycloheximide or ACTH, or both. For example, ACTH may increase both phospholipid turnover (degradation) and net synthesis, but the increase in turnover may only be apparent during blockade of phospholipid synthesis by cycloheximide. This possibility is diminished by the fact that we have not seen any effects of ACTH alone on prelabelled PI in pulse-chase labelling experiments, and ACTH provokes only a modest increase in [32P]Pi incorporation, which seems to be fully accounted for by the increase in phospholipid mass. Concerning the second possibility, cycloheximide does not appear to increase phospholipid degradation and turnover in the absence of ACTH (if anything, there is a small increase in phospholipid mass and labelling with either 32P04 or [3H]inositol). We are therefore left to conclude that the apparent increase in phospholipid degradation and turnover requires both cycloheximide and ACTH. The reason for this interaction is presently unclear, but perhaps ACTH-induced phospholipids exist in a pool whose degradation is metabolically linked to protein synthesis, or perhaps another hormonal event, e.g., a change in Ca2+, is needed in addition to inhibition of protein synthesis. Although the mechanism whereby cycloheximide (or puromycin) and ACTH interact to increase phospholipid degradation and turnover is unknown, the present observation is of importance for several reasons. First, this effect may explain, or contribute to, previously observed effects of cycloheximide on hormonally induced changes in phospholipid metabolism [l-7]. Second, in studies where 32P-labelling is employed acutely to monitor hormonal effects on phospholipid metabolism, such labelling may not reflect changes in phospholipid mass during combined cycloheximide-hormone treatment and may be difficult to interpret. Third, inhibitor-induced changes in phospholipid metabolism could be as important as inhibition of protein synthesis for explaining inhibition of other hormonal effects (note: we have observed similar effects of cycloheximide in the presence of insulin in other tissues). Fourth, failure to observe an inhibitory effect of cycloheximide during hormone action may suggestt hat a generalized increase in phospholipids is not required for cycloheximide-insensitive hormonal effects, but a mediatory role for phospholipid metabolism cannot be entirely ruled out, because. in some experimental conditions, increases in diacylglycerol and phosphatidic acid may yet be present. Obviously, these factors must be kept in mind when protein synthesis inhibitors are used to evaluate requirements for effects of hormones and other agents. This work was supported by funds from the National Institutes of Health (Grant No. 1 R01 HL 28290-02) and the Research Service of the Veterans Administration.",
year = "1984",
month = apr,
day = "18",
doi = "10.1016/0005-2760(84)90336-9",
language = "English (US)",
volume = "793",
pages = "317--320",
journal = "BBA - Specialised Section On Lipids and Related Subjects",
issn = "1388-1981",
publisher = "Elsevier",
number = "2",
}