The extracellular signal-regulated kinase (ERK) pathway is involved in human sperm function and modulated by the superoxide anion

Abstract

Our aim was to ascertain the role of the extracellular signal-regulated protein kinase (ERK) pathway in human sperm capacitation induced by fetal cord serum ultrafiltrate (FCSu) and its regulation by the superoxide anion (O(2)(-)*). Immunoblotting indicated the presence of Shc, Grb2, Ras(p21), Raf and ERK1 and 2 (ERK1/2) in spermatozoa. Grb2, Ras(p21), Raf and MEK inhibitors dose-dependently prevented sperm capacitation and protein tyrosine phosphorylation, without modifying sperm O(2)(-)* production. Therefore, the whole ERK cascade plays a role in capacitation, downstream of O(2)(-)* but upstream of protein tyrosine phosphorylation. Upon incubation with FCSu, the early (5 min) increase in ERK1/2 activity (as shown by double phosphorylation of the Thr-Glu-Tyr motif) was followed by an important decrease over the next 2 h; superoxide dismutase did not change this pattern. The phosphorylation of the Thr-Glu-Tyr motif present in other sperm proteins (16-33 kDa) also increased (5 min incubation with FCSu) and then progressively decreased, and this effect was regulated by O(2)(-)*, MEK and cAMP. The phospho-Ser/Thr-Pro content (characteristic of ERK1/2 substrates) of Triton-insoluble proteins (75 and 80 kDa) increased during capacitation and also appeared to be regulated by O(2)(-)* and the ERK pathway. Inhibition of ERK1/2 activation reduced lysophosphatidylcholine-induced acrosome reaction and the associated protein tyrosine phosphorylation. These results support a role for the ERK pathway in human sperm function.