Induction of MAPK phosphorylation by prosaposin and prosaptide in PC12 cells

Prosaposin is a 66 kDa glycoprotein which has neurotrophic activity in vitro and in vivo. The neurotrophic sequence ((8)CEFLVKEVTKLIDNNKTEKEL(29)L) within prosaposin has been located to the amino terminal portion of the saposin C domain. This 22-mer peptide, prosaptide, has neurotrophic activity equivalent to prosaposin. We present binding studies using I-125-prosaposin and I-125-prosaptide which revealed a single class of specific binding sites with a Kd of 2.5 nM and 18.3 nM, respectively. Both prosaposin and prosaptide rapidly stimulated protein tyrosine phosphorylation in PC12 cells and increased phosphorylation of MAPK 20-fold especially of p44 MAPK which peaked at 5 minutes of stimulation and then rapidly declined. Treatment of PC12 cells with a mutant 22-mer prosaptide ((21)Asn to (21)Asp) did not induce phosphorylation. These findings suggest a role for MAPK in signal transduction by prosaposin. (C) 1996 Academic Press