Lin H Y, Thacore H R, Davis F B, Davis P J
Department of Medicine, Albany Medical College, New York 12208, USA.
J Cell Physiol. 1996 May;167(2):269-76. doi: 10.1002/(SICI)1097-4652(199605)167:2<269::AID-JCP10>3.0.CO;2-3.
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.
L-甲状腺素（L-T4）可增强人γ干扰素（IFN-γ）在HeLa细胞中的抗病毒活性。我们将甲状腺激素及其类似物以以下方式加入细胞：1）在1.0 IU/ml的IFN-γ处理24小时之前进行24小时预处理；2）与IFN-γ共同处理24小时；3）在细胞与IFN-γ孵育20小时后单独处理4小时；4）进行24小时预处理并与IFN-γ共同处理24小时。然后检测IFN-γ的抗病毒效果。L-T4使IFN-γ的抗病毒作用增强，病毒产量降低超过两个对数，相当于IFN抗病毒效果增强100倍以上。3,3',5-L-三碘甲状腺原氨酸（L-T3）与IFN-γ共同孵育24小时时与L-T4效果相同，但仅共同孵育4小时时效果不如L-T4。D-T4、D-T3、3,3',5-三碘甲状腺乙酸（三碘乙酸）、四碘甲状腺乙酸（四碘乙酸）和3,5-二碘甲状腺原氨酸（T2）无活性。在IFN-γ处理前用L-T4预孵育24小时时，四碘乙酸可阻断L-T4的增强作用，但在IFN-γ孵育20小时后与L-T4共同孵育4小时时，四碘乙酸并不抑制L-T4的作用。反三碘甲状腺原氨酸（rT3）也可增强IFN-γ的抗病毒作用，但仅在预孵育模型中有效。此外，rT3预孵育和L-T3共同孵育的效果具有相加性，可使IFN-γ的效果增强100倍。当将L-T4、L-T3或rT3与环己酰亚胺（5微克/毫升）加入细胞中24小时，然后在24小时IFN-γ暴露前去除时，三种碘甲状腺原氨酸的增强作用被完全抑制。相比之下，L-T4或L-T3共同孵育4小时对IFN-γ的增强作用不受环己酰亚胺（25微克/毫升）的抑制。这些研究证明了甲状腺激素增强IFN-γ作用的两种机制：1）一种依赖蛋白质合成的机制，表现为L-T4、L-T3或rT3预孵育增强IFN-γ的抗病毒作用，以及四碘乙酸和环己酰亚胺对增强作用的抑制；2）一种不依赖蛋白质合成（翻译后）的机制，不受四碘乙酸或环己酰亚胺的抑制，表现为L-T4或L-T3但不是rT3与IFN-γ共同孵育4小时。依赖蛋白质合成的途径对rT3有反应，rT3是一种通常认为对蛋白质合成影响很小的甲状腺激素类似物。此前尚未描述过可调节IFN-γ抗病毒作用的翻译后机制。
