Oxidative inactivation of calcineurin by Cu,Zn superoxide dismutase G93A, a mutant typical of familial amyotrophic lateral sclerosis

Calcineurin is a serine/threonine phosphatase involved in a wide range of c ellular responses to calcium mobilizing signals. Previous evidence supports the notion of the existence of a redox regulation of this enzyme, which mi ght be relevant for neurodegenerative processes, where an imbalance between generation and removal of reactive oxygen species could occur. In a recent work, we have observed that calcineurin activity is depressed in two model s for familial amyotrophic lateral sclerosis (FALS) associated with mutatio ns of the antioxidant enzyme Cu,Zn superoxide dismutase (SOD1), namely in n euroblastoma cells expressing either SOD1 mutant G93A or mutant H46R and in brain areas from G93A transgenic mice. In this work we report that while wild-type SOD1 has a protective effect, c alcineurin is oxidatively inactivated by mutant SOD1s in vitro; this inacti vation is mediated by reactive oxygen species and Gan be reverted by additi on of reducing agents. Furthermore, we show that calcineurin is sensitive t o oxidation only when it is in an 'open', calcium-activated conformation, a nd that G93A-SOD1 must have its redox-active copper site available to subst rates in order to exert its pro-oxidant properties on calcineurin. These fi ndings demonstrate that both wild-type and mutant SOD1s can interfere direc tly with calcineurin activity and further support the possibility of a rele vant role for calcineurin-regulated biochemical pathways in the pathogenesi s of FALS.