Abstract
Ca2+ has been recently reported to be required for high rates of translational initiation in GH3 pituitary cells (Chin, K.-V., Cade, C., Brostrom, C.O., Galuska, E.M., and Brostrom, M.A. (1987) J. Biol. Chem. 262, 16509-16514). In the present investigation low concentrations of the Ca2+ ionophores, A23187 and ionomycin, were found to rapidly suppress the Ca2+-dependent component of protein synthesis in GH3 cells. More ionophore was required to inhibit amino acid incorporation into protein as extracellular Ca2+ was increased. Pre-existing inhibitions of protein synthesis produced by low concentrations of ionophore at low extracellular Ca2+ concentrations were reversed by adjustment to high extracellular Ca2+. Treatment with ionophore reduced the cellular contents of polysomes and 43 S preinitiation complex to values equivalent to those found for Ca2+-depleted cells. Average ribosomal transit times were unaffected by ionophore, and treated cells retained the ability to accumulate polysomes when incubated with cycloheximide. Cell types, such as HeLa and Chinese hamster ovary, that normally display only a modest Ca2+-dependent component of protein synthesis, manifested a strong underlying Ca2+ dependence in amino acid incorporation and polysome formation following treatment with low concentrations of ionophore. Protein synthesis in GH3 or HeLa cells during recovery from heat shock and arsenite treatment was not affected by cellular Ca2+ depletion or ionophore treatment. On the basis of these results, Ca2+ ionophore is proposed to inhibit Ca2+-dependent translational initiation through facilitating the mobilization of sequestered intracellular Ca2+.
Highlights
Mal material and a lower content of 60 S ribosomal subunits Effect of Ca2' Ionophores on Protein Synthesis inOther Cell and 80 S monosomes than Ca2+-depletedcells as determined Types- protein synthesis from normal hepatocytes following lysisin detergent-containing buffer, sucrose density [2, 3], GH3 (1, 8 ), and C6 ( 4 ) is readily inhibited bylow centrifugation, and subsequent absorption scanning a t 254 extracellular Ca2+(1mM EGTA), the process is only modestly nm (Fig. 3, A and D).Such changes are consistent with rates affected in a variety of other cell types such as CHO and of translational initiation that aremuch slower than rates of HeLa ( 4 )
The results of this report strongly support the conclusion tested, including CHO, HeLa, and PC12 adrenal cells, in a that Ca2+ionophores, such as A23187 and ionomycin, selecmanner that was facilitated by low extracellular Ca2+concen- tively inhibit the Ca2+-dependentcomponent of protein syntrations
Representative amino acid incorporation data are thesis by mobilizing the cation from intracellularsites of provided for the response of HeLa cells incubated at low. Cell types such as GH3, that are susceptible to mM EGTA) and physiologic (1mM free) Ca2+to increasing relatively complete depletion of intracellular sequestered Ca2+ concentrations of A23187 or ionomycin (Table 111).Controls stores by treatment with EGTA, responded to theionophore containing EGTA incorporated amino acid at approximately at physiologic extracellular Ca2+concentrationsas though 70% the rate of cells exposed to Ca2+.Protein synthesis in they were Ca2+depleted
Summary
Charles 0.Brostrom, Khew Voon Chin$, Wai Lam Wong, Christina Cadet, and Margaret A. Mal material and a lower content of 60 S ribosomal subunits Effect of Ca2' Ionophores on Protein Synthesis inOther Cell and 80 S monosomes than Ca2+-depletedcells as determined Types- protein synthesis from normal hepatocytes following lysisin detergent-containing buffer, sucrose density [2, 3], GH3 (1, 8 ) , and C6 ( 4 ) is readily inhibited bylow centrifugation, and subsequent absorption scanning a t 254 extracellular Ca2+(1mM EGTA), the process is only modestly nm (Fig. 3, A and D).Such changes are consistent with rates affected in a variety of other cell types such as CHO and of translational initiation that aremuch slower than rates of HeLa ( 4 ). The incubation was terminated by the or normal Ca2+retained the ability to accumulate polysomes addition of trichloroacetic acid and protein-associated radioactivity when challenged subsequently with cycloheximide to inhibit determined
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
