CYCLIC AMP-DEPENDENT REGULATION OF ORNITHINE DECARBOXYLASE ACTIVITY IN CHINESE-HAMSTER OVARY CELLS MAINTAINED WITH A SALTS-GLUCOSE MEDIUM

  • 1 January 1978
    • journal article
    • research article
    • Vol. 4  (5) , 375-387
Abstract
Ornithine decarboxylase [EC 4.1.1.17] activity (ODC) increased about 7-fold 6-8 h following 10 mM asparagine (ASN) addition to confluent cultures that had been previously serum deprived and then placed in a salts/glucose medium. Optimal concentrations of dibutyryl cyclic[c]AMP (dB cAMP) when incubated with the ASN caused up to a 50-fold increase in the activity of this enzyme after 7-8 h. The enhancement of ODC activity by ASN and dB cAMP was not sensitive to continuous (0-7 h) treatment with actinomycin D but similar treatment with cycloheximide depressed enzyme activity 40-60%. The synergistic stimulation of ODC activity by dB cAMP added with ASN was dose-dependent and the dB cAMP stimulation of ODC activity displayed an absolute requirement for ASN when cells were maintained in the salts/glucose medium. The addition of dB cAMP further enhanced ODC activity above the levels produced by addition of various levels of ASN (1-40 mM) to the salts/glucose medium. Other agents which elevated cAMP levels such as 1-methyl-3-isobutylxanthine (IBMX) also enhanced ODC activity when administered with ASN. Additionally, treatment with sodium butyrate at concentrations ranging from 0.001 mM-5.0 mM did not elevate ODC activity above the activity obtained with ASN alone. Addition of dB cAMP at various times after placing cells in salts/glucose medium with ASN further stimulated ODC activity only when added during the first 3-4 h. These results demonstrate the involvement of cAMP in the ASN mediated stimulation of ODC activity using cells maintained in a salts/glucose medium.

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