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Phosphorylation of the beta1 integrin cytoplasmic domain: toward an understanding of function and mechanism
J Mulrooney1, K Foley, S Vineberg
1Department of Biology, Wesleyan University, Middletown, Connecticut 06459-0170, USA.
Abstract:
As F9 stem cells differentiate into parietal endoderm they form focal adhesion sites. There is a concomitant decrease in the level of phosphorylation of S785 in the cytoplasmic domain of the beta1 integrin subunit. Previous transfection studies demonstrate that site-specific mutations at this residue, mimicking different phosphorylation states, can alter the subcellular localization of the subunit in differentiating F9 cells. We now extend these observations in an attempt to substantiate the function of beta1 phosphorylation and determine how the phosphorylation levels are regulated. We show that treatment of parietal endoderm with okadaic acid induces an increase in beta1 phosphorylation and selective loss of beta1 from focal adhesion sites. Using a PCR approach, we identify two phosphatases expressed in parietal endoderm, including PP2A. Using a crosslinking approach, where antibodies are added to live cells, we show that the catalytic subunit of PP2A co-immunoprecipitates with beta1. Immunocytochemistry shows PP2A colocalizing to focal adhesion sites with beta1. In addition integrin-linked kinase (ILK) co-immunoprecipitates with beta1 in parietal endoderm and localizes to focal adhesion sites. Okadaic acid treatment significantly decreases the level of ILK associated with beta1. A possible role for regulated beta1 phosphorylation in cell migration is discussed.
Insights
Beta1 integrin phosphorylation at S785 decreases during F9 cell differentiation. Protein phosphatase 2A (PP2A) and integrin-linked kinase (ILK) regulate this phosphorylation, impacting focal adhesion dynamics and potentially cell migration.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- F9 stem cells differentiate into parietal endoderm, forming focal adhesion sites.
- During differentiation, phosphorylation of beta1 integrin at S785 decreases.
- Previous studies suggest S785 phosphorylation state affects beta1 integrin localization.
Purpose of the Study:
- To investigate the functional role of beta1 integrin phosphorylation.
- To elucidate the regulatory mechanisms controlling beta1 phosphorylation levels.
- To understand the impact of phosphorylation on focal adhesion dynamics.
Main Methods:
- Treatment of parietal endoderm with okadaic acid (phosphatase inhibitor).
- Polymerase Chain Reaction (PCR) to identify phosphatases.
- Crosslinking and co-immunoprecipitation to study protein interactions.
- Immunocytochemistry to visualize protein localization.
Main Results:
- Okadaic acid treatment increased beta1 integrin phosphorylation and reduced its presence at focal adhesions.
- Protein phosphatase 2A (PP2A) and integrin-linked kinase (ILK) were identified in parietal endoderm.
- PP2A and ILK co-immunoprecipitated with beta1 integrin and localized to focal adhesions.
- Okadaic acid treatment decreased ILK association with beta1 integrin.
Conclusions:
- Regulated phosphorylation of beta1 integrin, potentially by PP2A and ILK, influences its localization at focal adhesions.
- These findings suggest a role for beta1 integrin phosphorylation in controlling cell adhesion and migration dynamics during differentiation.