Publication: Molecular role of sulfated glycoprotein-1
(SGP-I/Prosaposin) in Sertoli cells
Authors
Morales, C.R. ; El-Alfy, M. ; Zhao, Q. ; Igdoura, S.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
Sulfated Glycoprotein- 1 (SGP- 1) is a major
polypeptide secreted by rat Sertoli cells. Sequence
analysis revealed a 70% sequence similarity with human
prosaposin and a 80% similarity with mouse prosaposin.
Both human and mouse prosaposin are 65-70 kDa
proteins cleaved in the lysosomes into four 10-15 kDa
proteins designated saposins A, B, C and D. Lysosomal
saposins function as enzymatic activators that promote
the hydrolysis of certain glycolipids. SGP-1 (70 kDa)
was first considered as being exclusively secreted to the
extracellular space. However, recent immunocytochemical
studies using an anti SGP-1 antibody
demonstrated the presence of this protein in Sertoli cell
lysosomes. In addition Sertoli cell lysosomes isolated by
cellular fractionation were found to contain a 65 kDa
form of SGP-1 or lysosomal prosaposin, as well as, the
15 kDa saposins. Morphological and immunocytochemical
evidences also indicated that both prosaposin
and saposins may reach Sertoli cell phagosomes by
lysosomal fusion. These phagosomes contain
cytoplasmic residual bodies detached from spermatids
during spermiation. Thus, prosaposin and their derived
saposins must play a role in the hydrolysis of membrane
glycolipids present in phagocytosed residual bodies. On
the other hand, the function of the secreted form of SGP-
1 is still unclear. However, SGP-1 was seen to interact
with the plasma membrane of developing spermatids.
Due to its capacity to bind certain types of gangliosides,
SGP-1 appears to act as glycolipid transfer between
Sertoli cells and the developing spermatids.
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