Abstract
We have investigated the binding and internalization of α2- macroglobulin and serum albumin by human placental syncytiotrophoblast cells in vitro. The time course (obtained at 4°C) of α2-macroglobulin binding indicated that an equilibrium was reached after 4 h. The binding of 125I- labelled α2-macroglobulin to syncytiotrophoblast cells was competitively reduced in the presence of excess unlabelled α2-macroglobulin. When the concentration-dependence of binding was examined over a wide concentration range, non-linear regression analysis yielded a K(d) of 6.4 nM. In the case of albumin, binding was weak and ligand dissociated from the cell surface during aqueous washing making it impractical to analyze the binding reaction. In other experiments, syncytiotrophoblast cells were incubated with 125I- labelled α2-macroglobulin at 37°C. Under these conditions, trypsin- resistant cell-associated radioactivity increased with time consistent with ligand internalization. 125I-Labelled-ligand was internalized with a t 1/4 of about 5 min. After a lag period some radioactivity was released back into the incubation medium. When measured at times up to 210 min, this was found to consist of mostly TCA-precipitable material that had been lost from the cell surface. However, when the incubation was extended to 24 h, almost 15% of the initial cell-associated radioactivity was released to the extracellular medium as TCA-soluble material, consistent with a slow rate of ligand degradation. The specific binding of 65Zn-labelled α2M was similar to that of the 125I-labelled ligand and trypsin-resistance measurements provided evidence of α2M-mediated 65Zn uptake. These results support a role for syncytiotrophoblast in the metabolism of α2-macroglobulin during pregnancy and are also consistent with a role for α2-macroglobulin in the maternal-fetal transport of zinc.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 427-435 |
| Number of pages | 9 |
| Journal | Journal of Cellular Biochemistry |
| Volume | 68 |
| Issue number | 4 |
| DOIs | |
| State | Published - Mar 15 1998 |
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Keywords
- Albumin
- Placenta
- Zinc
- α-macroglobulin
ASJC Scopus subject areas
- Biochemistry
- Cell Biology
Cite this
Uptake of 125I-labelled α2-macroglobulin and albumin by human placental syncytiotrophoblast in vitro. / Douglas, Gordon C; Moreira-Cali, Patricia; King, Barry F.; Lonnerdal, Bo.
In: Journal of Cellular Biochemistry, Vol. 68, No. 4, 15.03.1998, p. 427-435.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Uptake of 125I-labelled α2-macroglobulin and albumin by human placental syncytiotrophoblast in vitro
AU - Douglas, Gordon C
AU - Moreira-Cali, Patricia
AU - King, Barry F.
AU - Lonnerdal, Bo
PY - 1998/3/15
Y1 - 1998/3/15
N2 - We have investigated the binding and internalization of α2- macroglobulin and serum albumin by human placental syncytiotrophoblast cells in vitro. The time course (obtained at 4°C) of α2-macroglobulin binding indicated that an equilibrium was reached after 4 h. The binding of 125I- labelled α2-macroglobulin to syncytiotrophoblast cells was competitively reduced in the presence of excess unlabelled α2-macroglobulin. When the concentration-dependence of binding was examined over a wide concentration range, non-linear regression analysis yielded a K(d) of 6.4 nM. In the case of albumin, binding was weak and ligand dissociated from the cell surface during aqueous washing making it impractical to analyze the binding reaction. In other experiments, syncytiotrophoblast cells were incubated with 125I- labelled α2-macroglobulin at 37°C. Under these conditions, trypsin- resistant cell-associated radioactivity increased with time consistent with ligand internalization. 125I-Labelled-ligand was internalized with a t 1/4 of about 5 min. After a lag period some radioactivity was released back into the incubation medium. When measured at times up to 210 min, this was found to consist of mostly TCA-precipitable material that had been lost from the cell surface. However, when the incubation was extended to 24 h, almost 15% of the initial cell-associated radioactivity was released to the extracellular medium as TCA-soluble material, consistent with a slow rate of ligand degradation. The specific binding of 65Zn-labelled α2M was similar to that of the 125I-labelled ligand and trypsin-resistance measurements provided evidence of α2M-mediated 65Zn uptake. These results support a role for syncytiotrophoblast in the metabolism of α2-macroglobulin during pregnancy and are also consistent with a role for α2-macroglobulin in the maternal-fetal transport of zinc.
AB - We have investigated the binding and internalization of α2- macroglobulin and serum albumin by human placental syncytiotrophoblast cells in vitro. The time course (obtained at 4°C) of α2-macroglobulin binding indicated that an equilibrium was reached after 4 h. The binding of 125I- labelled α2-macroglobulin to syncytiotrophoblast cells was competitively reduced in the presence of excess unlabelled α2-macroglobulin. When the concentration-dependence of binding was examined over a wide concentration range, non-linear regression analysis yielded a K(d) of 6.4 nM. In the case of albumin, binding was weak and ligand dissociated from the cell surface during aqueous washing making it impractical to analyze the binding reaction. In other experiments, syncytiotrophoblast cells were incubated with 125I- labelled α2-macroglobulin at 37°C. Under these conditions, trypsin- resistant cell-associated radioactivity increased with time consistent with ligand internalization. 125I-Labelled-ligand was internalized with a t 1/4 of about 5 min. After a lag period some radioactivity was released back into the incubation medium. When measured at times up to 210 min, this was found to consist of mostly TCA-precipitable material that had been lost from the cell surface. However, when the incubation was extended to 24 h, almost 15% of the initial cell-associated radioactivity was released to the extracellular medium as TCA-soluble material, consistent with a slow rate of ligand degradation. The specific binding of 65Zn-labelled α2M was similar to that of the 125I-labelled ligand and trypsin-resistance measurements provided evidence of α2M-mediated 65Zn uptake. These results support a role for syncytiotrophoblast in the metabolism of α2-macroglobulin during pregnancy and are also consistent with a role for α2-macroglobulin in the maternal-fetal transport of zinc.
KW - Albumin
KW - Placenta
KW - Zinc
KW - α-macroglobulin
UR - http://www.scopus.com/inward/record.url?scp=0032520255&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0032520255&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1097-4644(19980315)68:4<427::AID-JCB3>3.0.CO;2-S
DO - 10.1002/(SICI)1097-4644(19980315)68:4<427::AID-JCB3>3.0.CO;2-S
M3 - Article
C2 - 9493906
AN - SCOPUS:0032520255
VL - 68
SP - 427
EP - 435
JO - Journal of Cellular Biochemistry
JF - Journal of Cellular Biochemistry
SN - 0730-2312
IS - 4
ER -