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. 2006 Sep 18;26(22):8562–8571. doi: 10.1128/MCB.00497-06

FIG. 7.

FIG. 7.

Expression of Tyk2 positively regulates mitochondrial respiration. (A) Under unstimulated (no IFN-α/β) conditions, Tyk2 expression but not its kinase activity is required for optimal mitochondrial respiration in pro-B cells via modulating complex I, III, and IV activities, whereas (B) under IFN-α/β-stimulated conditions, there are two possible outcomes depending on the length of exposure to IFN-β. (i) Under shorter incubation conditions (20 h), Tyk2 expression as well as its kinase activity (at least in part through Stat3 activation) are required to maintain oxygen consumption. Tyk2 kinase activity and Stat3 activation appear to target, either directly or indirectly, complex I function (+), even though complexes III and IV are also modulated to a lesser extent (+/−) under similar conditions. (ii) Under prolonged incubation with IFN-β (>24 h), Tyk2 kinase-dependent Stat3 activation induces apoptosis and the release of cytochrome c (Cyt c).