title: Thyroid hormone analogues potentiate the antiviral action of interferon-gamma by two mechanisms.
abstract: L-thyroxine (L-T4) potentiates the antiviral activity of human interferon-gamma (IFN-gamma) in HeLa cells. We have added thyroid hormone and analogues to cells either 1) for 24 h pretreatment prior to 24 h of IFN-gamma (1.0 IU/ml), 2) for 24 h cotreatment with IFN-gamma, 3) for 4, after 20 h cell incubation with IFN-gamma, alone, or 4) for 24 h pretreatment and 24 h cotreatment with IFN-gamma. The antiviral effect of IFN-gamma was then assayed. L-T4 potentiated the antiviral action of IFN-gamma by a reduction in virus yield of more than two logs, the equivalent of a more than 100-fold potentiation of the IFN's antiviral effect. 3,3 of the IFN's antiviral effect. 3,3',5-L-triiodothyronine (L-T3) was as effective as L-T4 when coincubated for 24 h with IFN-gamma but was less effective than L-T4 when coincubated for only 4 h. D-T4, D-T3, 3,3',5-triiodothyroacetic acid (triac), tetraiodothyroacetic acid (tetrac), and 3,5-diiodothyronine (T2) were inactive. When preincubated with L-T4 for 24 h prior to IFN-gamma treatment, tetrac blocked L-T4 potentiation, but, when coincubated with L-T4 for 4 h after 20 h IFN-gamma, tetrac did not inhibit the L-T4 effect. 3,3',5-L-triiodothyronine (rT3) also potentiated the antiviral action of IFN-gamma, but only in the preincubation model. Furthermore, the effects of rT3 preincubation and L-T3 coincubation were additive, resulting in 100-fold potentiation of the IFN-gamma effect. When L-T4, L-T3, or rT3, plus cycloheximide (5 micrograms/ml), was added to cells for 24 h and then removed prior to 24 h IFN-gamma exposure, the potentiating effect of the three iodothyronines was completely inhibited. In contrast, IFN-gamma potentiation by 4 h of L-T4 or L-T3 coincubation was not inhibited by cycloheximide (25 micrograms/ml). These studies demonstrate two mechanisms by which thyroid hormones can potentiate IFN-gamma's effect: 1) a protein synthesis-dependent mechanism evidenced by enhancement of IFN-gamma's antiviral action by L-T4, L-T3, or rT3 preincubation, and inhibition of enhancement by tetrac and cycloheximide, and 2) a protein synthesis-independent (posttranslational) mechanism, not inhibited by tetrac or cycloheximide, demonstrated by 4 h coincubation of L-T4 or L-T3, but not rT3, with IFN-gamma. The protein synthesis-dependent pathway is responsive to rT3, a thyroid hormone analogue generally thought to have little effect on protein synthesis. A posttranslational mechanism by which the antiviral action of IFN-gamma can be regulated has not previously been described.
authors.affiliation: Department of Medicine, Albany Medical College, New York 12208, USA.
authors.forename: H Y
authors.initials: HY
authors.lastname: Lin
authors.forename: H R
authors.initials: HR
authors.lastname: Thacore
authors.forename: F B
authors.initials: FB
authors.lastname: Davis
authors.forename: P J
authors.initials: PJ
authors.lastname: Davis
mesh_terms: D000998:Antiviral Agents / Q000494:pharmacology*; D003513:Cycloheximide / Q000494:pharmacology; D004104:Diiodothyronines / Q000494:pharmacology; D004357:Drug Synergism; D006367:HeLa Cells / Q000187:drug effects / Q000276:immunology / Q000821:virology; D006801:Humans; D007371:Interferon-gamma / Q000187:drug effects / Q000494:pharmacology*; D014176:Protein Biosynthesis; D012680:Sensitivity and Specificity; D013963:Thyroid Hormones / Q000494:pharmacology*; D013974:Thyroxine / Q000031:analogs & derivatives / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D000998:Antiviral Agents; D004104:Diiodothyronines; D013963:Thyroid Hormones; D014284:Triiodothyronine; C030103:3,5-diiodothyronine; D007371:Interferon-gamma; D003513:Cycloheximide; D013974:Thyroxine