A role for geranylgeranylation in interleukin-1β secretion

Objective. Mevalonate kinase deficiency (MKD) is an autosomal-recessive disorder characterized by recurring episodes of inflammation. MK catalyzes the phosphorylation of naevalonic acid, which is an early step in isoprenoid biosynthesis. The goal of our study was to determine whether a temporary shortage of certain isoprenoid end products and/or the accumulation of mevalonic acid is the cause of interleukin-1β (IL-1β) secretion in MKD. Methods. We studied the effect of the addition of intermediate metabolites and inhibitors of the isoprenoid biosynthesis pathway on IL-1β secretion by peripheral blood mononuclear cells (PBMCs) of patients with MKD and healthy controls. Results. Inhibition of enzymes involved in geranylgeranyl pyrophosphate (GGPP) synthesis or geranylgeranylation of proteins led to a marked increase of lipopolysaccharide-stimulated IL-1β secretion in PBMCs of control subjects. Furthermore, the increased IL-1β secretion by PBMCs of patients with MKD was reversed by supplementation with GGPP as well as with mevalonic acid. IL-1β secretion was increased only when control PBMCs were incubated with excessive amounts of mevalonic acid. Finally, a reduction in IL-1β secretion by MKD PBMCs was also observed when sterol biosynthesis was inhibited, favoring nonsterol isoprenoid biosynthesis. Conclusion. Our results indicate that a shortage of geranylgeranylated proteins, rather than an excess of mevalonate, is likely to cause increased IL-1β secretion by PBMCs of patients with MKD.