Secretion of sphingolipid hydrolase activator precursor, prosaposin

Hineno, Takashi; Sano, Akira; Kondoh, Keiji; Ueno, Shu‐ichi; Kakimoto, Yasuo; Yoshida, Kenichi

doi:10.1016/s0006-291x(05)80236-0

Cited by 108 publications

(69 citation statements)

References 18 publications

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“…The circumstantial evidence that prosaposin not only is a lysosomal precursor ofthe saposin proteins but also has other functions, especially in the nervous system, can be summarized as follows: Prosaposin exists as an unprocessed protein in human (6) and rat (7) brain and in cerebrospinal fluid (5,23). Immunocytochemical studies using a prosaposinspecific antibody demonstrated high concentrations of prosaposin in human cortical neurons (unpublished data).…”

Section: Discussionmentioning

confidence: 93%

Identification of prosaposin as a neurotrophic factor.

O’Brien

Carson

Seo

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

216

171

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Prosaposin was identified as a neurotrophic factor stimulating neurite outgrowth in murine neuroblastoma (NS20Y) cells and choline acetyltranferase (ChAT) activity in human neuroblastoma (SK-N-MC) cells. The four naturally occurring saposs, which are derived by proteolytic processing of prosaposin, were tested for activity. Saposin C was found to be active, whereas saposns A, B, and D were inactive as neurotrophic factors. Dose-response curves demonstrated that nanomolar concentrations of prosaposin and saposin C stimulated neurite outgrowth and increased ChAT activity. Prosaposin and saposin C exerted activity by a mechanlsm independent of nerve growth factor, brain-derived neurotrophic factor, and neurotrophin 3. Binding assays uing saposin C as a ilgand gave two saturable binding constants, a hig-affnity (Kd = 19 pM) and a low-affinity (Kd = 1 uM) constant, with 2000 and 15,000 sites per NS20Y cell, respectively. Phosphorylation stimulation experiments demonstrated that brief treatment with prosaposin or saposin C enhanced phospholation of a variety of proteins, some of which contained phosphorylated tyrosine(s). Since both cell lines were also stimulated by ciary neurotrophic factor (CNTF) as well as prosaposin, inhibition was tested by utilizing an anti-gpl30 monoclonal antibody, which s lly inhibited CNTF stimulation; thls antibody did not inhibit prosaposin or saposi C smulation. These results indicate that prosaposin and saposin C are neurotrophic factors which initiate signal transduction by binding to a high-afinity receptor that induces protein phosphorylation.Prosaposin is the precursor of the lysosomal saposin proteins, which are required for hydrolysis ofglycosphingolipids by lysosomal hydrolases (1, 2). In addition to its role as a lysosomal precursor, prosaposin is presumed to have additional functions, since it exists as a secretory protein in human milk, cerebrospinal fluid, and seminal plasma (3-5); it is present in unprocessed form in high concentrations in human (6) and rat (7) brain; its mRNA is abundant in brain and dorsal root ganglia during embryonic development (8); it is present predominantly in neurons after immunostaining (9); and it occurs as an integral membrane component (10).Recently we demonstrated that prosaposin binds gangliosides with high affinity and facilitates their transfer from micelles to membranes (11). Since gangliosides have been shown to promote neurite outgrowth in cultured neuronal cells (12-14), we investigated whether prosaposin was also active. In this report we identify prosaposin as a potent neurotrophic factor and locate the active region to the saposin C domain. (PBS), and fixed in Bouins solution (30 min). After the fixative had been removed, neurite outgrowth was scored under a phase-contrast microscope. Cells bearing neurites longer than 1 cell diameter were scored as positive, and 100 cells were counted in triplicate from different portions of each dish. Each assay was carried out in duplicate dishes. The average error of duplicates (40 assay...

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Section: Discussionmentioning

confidence: 93%

Identification of prosaposin as a neurotrophic factor.

O’Brien

Carson

Seo

et al. 1994

Proc. Natl. Acad. Sci. U.S.A.

216

171

View full text Add to dashboard Cite

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“…(31) Meanwhile, PSAP was found in cerebrospinal fluid and seminal plasma. (16) The phenomena of PSAP knock-out mice and distribution of PSAP in the body interested researchers in investigating the role of PSAP in the nervous system and prostate cancer. Koochekpour et al (24) studied the role of PSAP in prostate cancer and found that PSAP played a role in regulating AR and PSA expression and cell activity.…”

Section: Discussionmentioning

confidence: 99%

“…(14) Secretory PSAP is a well-known pleiotropic growth factor found in secretory body fluid, such as seminal plasma, bile, cerebrospinal fluid, human milk, (15,16) as well as neuronal surface membrane.…”

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confidence: 99%

“…(13) Lysosomal PSAP is the precursor of four sphingolipid activator proteins (saposin A-D) and is involved in hydrolysis of sphingolipids within lysosome. (14) Secretory PSAP is a well-known pleiotropic growth factor found in secretory body fluid, such as seminal plasma, bile, cerebrospinal fluid, human milk, (15,16) as well as neuronal surface membrane. (17) The distribution of PSAP suggests it may have some specific extracellular functions.…”

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confidence: 99%

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Prosaposin, a regulator of estrogen receptor alpha, promotes breast cancer growth

Sun

et al. 2012

Cancer Science

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Prosaposin, a secreted protein, is a well-known pleiotropic growth factor. Although a previous report has indicated that prosaposin is overexpressed in breast cancer cell lines, the role of prosaposin in the development of breast cancer remains to be identified. Here, we first revealed that prosaposin upregulated estrogen receptor alpha expression, nuclear translocation and transcriptional activity by western blot, immunofluorescence assay and dual luciferase reporter gene assay, respectively. Furthermore, we demonstrated prosaposin upregulated estrogen receptor alpha expression through MAPK-signaling pathway using MAPK inhibitor. Proliferation assay and tumor xenograft experiments in nude mice (n = 6 per group) further confirmed prosaposin could promote breast cancer growth significantly in vitro and in vivo. These findings suggested that prosaposin might enhance estrogen receptor alpha-mediated signaling axis and play a role in breast cancer development and progression. (Cancer Sci 2012; 103: 1820-1825 B reast cancer is the most common malignancy and the main cause of death from cancers in women.(1) The carcinogenesis of breast cancer is frequently hormone-dependent. The female sex-steroid hormone estrogen 17b-estradiol (E2) plays a prominent role in mediating the maturation, proliferation, differentiation, and influences the growth and development of breast cancer.(2) Numerous studies have indicated that E2 can induce and promote breast cancer and this process is mediated primarily by estrogen receptor alpha (ERa). (3)(4)(5) Estrogen receptor (ER) is a member of the steroid/nuclear receptor family of transcription regulators, while ERa is the predominant receptor isoform expressed in breast cancer. Approximately 70% of breast cancer patients score positive for ERa at diagnosis.(6-9) Estrogen receptor alpha promotes cell growth, metastasis and also mediates resistance to apoptosis or immunosurveillance in breast cancer. (10)(11)(12) Prosaposin (PSAP) exists as a secretory protein (70 kDa) as well as a lysosomal protein (65 kDa). The molecular weight difference depends on the post-translational glycosylation. (13) Lysosomal PSAP is the precursor of four sphingolipid activator proteins (saposin A-D) and is involved in hydrolysis of sphingolipids within lysosome.(14) Secretory PSAP is a well-known pleiotropic growth factor found in secretory body fluid, such as seminal plasma, bile, cerebrospinal fluid, human milk, (15,16) as well as neuronal surface membrane.(17) The distribution of PSAP suggests it may have some specific extracellular functions. PSAP-deficiency in human and mice is lethal. (18,19) Prosaposin knock-out mice also present with a series of developmental abnormalities in the nervous system and male reproductive organs. (18,20) Recent investigations show that PSAP could prevent cell death or apoptosis and promote cell survival. (21,22) Koochekpour et al. (23) focus on the function of PSAP in prostate cancer and find PSAP is overexpressed in prostate cancer, and also upregulates androgen receptor (...

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“…Current evidence suggests that prosaposin is the only member of the saposin family with an extralysosomal location as a secretory protein (28)(29)(30) (15). We postulate that secretory prosaposin could transfer gangliosides to the plasma membrane and that integral membrane prosaposin could transfer gangliosides from one cytoplasmic location to another.…”

Section: Discussionmentioning

confidence: 99%