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 (8CEFLVKEVTKLIDNNKTEKEI29L) 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 125I-prosaposin and 125I-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 (21Asn to 21Asp) did not induce phosphorylation. These findings suggest a role for MAPK in signal transduction by prosaposin.
Campana
W M
WM
Department of Neurosciences, University of California, San Diego, School of Medicine, La Jolla, California, 92093, USA.
Hiraiwa
M
M
Addison
K C
KC
O'Brien
J S
JS
D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D006023:Glycoproteins / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors / Q000494:pharmacology*; D016716:PC12 Cells; D010766:Phosphorylation; D011869:Radioligand Assay; D051381:Rats; D049231:Saposins; D015398:Signal Transduction / Q000187:drug effects*
D006023:Glycoproteins; D009414:Nerve Growth Factors; C483345:PSAP protein, human; C483347:Psap protein, rat; D049231:Saposins; C101246:prosaptide; D017871:Calcium-Calmodulin-Dependent Protein Kinases