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Membrane glycoprotein PC-1 inhibition of insulin receptor function occurs via direct interaction with the receptor
1Department of Medicine, Mount Zion Medical Center, University of California San Francisco, USA.
Abstract:
Plasma cell membrane glycoprotein-1 (PC-1) inhibits insulin receptor (IR) tyrosine kinase activity and subsequent cellular signaling. PC-1 content is elevated in fibroblasts, muscle, and adipose tissue from insulin-resistant subjects, and its elevation correlates with in vivo insulin resistance. In vitro, when PC-1 is transfected and overexpressed in cultured cells, it inhibits IR tyrosine kinase activity. To determine the mechanism whereby PC-1 regulates the IR, we studied how PC-1 interacts with this protein. Overexpression of PC-1 in MCF-7 cells inhibited tyrosine kinase activity of the IR, but not of the IGF-I receptor. When the IR was immunocaptured by specific IR monoclonal antibodies, PC-1 was associated with this receptor. In contrast, after specific immunocapture, PC-1 was not associated with the IGF-I receptor. We next studied HTC cells that were overexpressing an IR alpha-subunit mutant. This IR mutant binds insulin but has a deletion in the tyrosine kinase regulatory domain located in amino acids 485-599. In contrast to normal IRs, PC-1 did not associate with this mutant and did not affect tyrosine kinase activity. To determine whether decreasing PC-1 expression would reverse the inhibition of tyrosine kinase activity, we treated MCF-7 cells overexpressing PC-1 with a monoclonal antibody to PC-1. This treatment decreased PC-1 levels; concomitantly, IR tyrosine kinase activity increased. In contrast, IGF-I receptor tyrosine kinase activity was not increased. These studies indicate, therefore, that PC-1 may inhibit the IR by interacting directly with a specific region in the IR alpha-subunit. These studies also raise the possibility that monoclonal antibodies to PC-1 could be a new treatment for insulin resistance.
Insights
Plasma cell membrane glycoprotein-1 (PC-1) inhibits insulin receptor (IR) activity, contributing to insulin resistance. Targeting PC-1 with antibodies may offer a novel therapeutic approach for managing insulin resistance.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Plasma cell membrane glycoprotein-1 (PC-1) is known to inhibit insulin receptor (IR) tyrosine kinase activity.
- Elevated PC-1 levels are observed in tissues of insulin-resistant individuals, correlating with the severity of insulin resistance.
Purpose of the Study:
- To elucidate the mechanism by which PC-1 regulates IR tyrosine kinase activity.
- To investigate the interaction between PC-1 and the IR.
- To explore the potential of targeting PC-1 as a therapeutic strategy for insulin resistance.
Main Methods:
- Overexpression of PC-1 in MCF-7 cells to assess its effect on IR and IGF-I receptor activity.
- Immunocapture assays to determine the association of PC-1 with the IR and IGF-I receptor.
- Studies using a mutant IR alpha-subunit lacking the tyrosine kinase regulatory domain.
- Treatment of PC-1 overexpressing cells with a monoclonal antibody against PC-1.
Main Results:
- PC-1 overexpression inhibited IR tyrosine kinase activity but not IGF-I receptor activity.
- PC-1 was found to associate with the IR but not the IGF-I receptor.
- PC-1 did not associate with or inhibit the tyrosine kinase activity of a mutant IR lacking a specific regulatory domain.
- Antibody-mediated reduction of PC-1 levels restored IR tyrosine kinase activity.
Conclusions:
- PC-1 directly interacts with a specific region of the IR alpha-subunit to inhibit its tyrosine kinase activity.
- These findings suggest that PC-1 plays a significant role in the pathogenesis of insulin resistance.
- Monoclonal antibodies targeting PC-1 represent a potential novel therapeutic intervention for insulin resistance.