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Altered localization and cytoplasmic domain-binding properties of tyrosine-phosphorylated beta 1 integrin
M W Johansson1, E Larsson, B Lüning
1La Jolla Cancer Research Foundation, California 92037.
Abstract:
We describe a novel approach to study tyrosine-phosphorylated (PY) integrins in cells transformed by virally encoded tyrosine kinases. We have synthesized a peptide (PY beta 1 peptide) that represents a portion of the cytoplasmic domain of the beta 1 integrin subunit and is phosphorylated on the tyrosine residue known to be the target of oncogenic tyrosine kinases. Antibodies prepared against the PY beta 1 peptide, after removal of cross-reacting antibodies by absorption and affinity purification, recognized the PY beta 1 peptide and the tyrosine-phosphorylated form of the intact beta 1 subunit, but did not bind the nonphosphorylated beta 1 peptide, the nonphosphorylated beta 1 subunit or other unrelated tyrosine-phosphorylated proteins. The anti-PY beta 1 antibodies labeled the podosomes of Rous sarcoma virus-transformed fibroblasts, but did not detectably stain nontransformed fibroblasts. The localization of the tyrosine phosphorylated beta 1 subunits appeared distinct from that of the beta 1 subunit. Adhesion plaques were stained by the anti-beta 1 subunit antibodies in Rous sarcoma virus-transformed fibroblasts plated on fibronectin, whereas neither podosomes nor adhesion plaques were labeled on vitronectin or on uncoated plates. Anti-phosphotyrosine antibodies labeled podosomes, adhesion plaques and cell-cell boundaries regardless of the substratum. One of the SH2 domains of the p85 subunit of phosphatidylinositol-3-kinase bound to the PY beta 1 peptide, but not to the non-phosphorylated beta 1 cytoplasmic peptide. Other SH2 domains did not bind to the PY beta 1 peptide. These results show that the phosphorylated form of the beta 1 integrin subunit is detected in a different subcellular localization than the nonphosphorylated form and suggest that the phosphorylation on tyrosine of the beta 1 subunit cytoplasmic domain may affect cellular signaling pathways.
Insights
Researchers developed a new method to detect tyrosine-phosphorylated beta 1 integrins in cancer cells. This novel antibody specifically targets the phosphorylated form, revealing its distinct location and potential role in cell signaling pathways.
Area of Science:
- Cell Biology
- Biochemistry
- Oncology
Background:
- Integrins are crucial cell surface receptors involved in cell adhesion and signaling.
- Tyrosine phosphorylation of integrins, particularly the beta 1 subunit, is implicated in cellular transformation and cancer progression.
- Understanding the localization and function of phosphorylated integrins is key to deciphering oncogenic signaling pathways.
Purpose of the Study:
- To develop a specific method for detecting tyrosine-phosphorylated beta 1 integrins in virally transformed cells.
- To investigate the subcellular localization of tyrosine-phosphorylated beta 1 integrins compared to their non-phosphorylated counterparts.
- To explore the potential functional implications of beta 1 integrin tyrosine phosphorylation in cellular signaling.
Main Methods:
- Synthesis of a specific peptide representing the tyrosine-phosphorylated cytoplasmic domain of the beta 1 integrin subunit (PY beta 1 peptide).
- Generation and purification of antibodies against the PY beta 1 peptide.
- Immunofluorescence microscopy to visualize the localization of phosphorylated beta 1 integrins in transformed and non-transformed fibroblasts.
- Co-immunoprecipitation assays to assess the interaction of the PY beta 1 peptide with SH2 domains of phosphatidylinositol-3-kinase.
Main Results:
- Novel antibodies specifically recognized tyrosine-phosphorylated beta 1 integrins but not non-phosphorylated forms or other proteins.
- Tyrosine-phosphorylated beta 1 integrins were localized to podosomes in Rous sarcoma virus-transformed fibroblasts, distinct from the localization of total beta 1 integrins.
- The phosphorylated beta 1 integrin peptide specifically bound to an SH2 domain of phosphatidylinositol-3-kinase, suggesting a role in signaling complex assembly.
Conclusions:
- The developed antibody provides a specific tool for studying tyrosine-phosphorylated beta 1 integrins.
- Tyrosine phosphorylation alters the subcellular localization of beta 1 integrins, suggesting distinct functional roles.
- Beta 1 integrin tyrosine phosphorylation may influence cellular signaling pathways, potentially through interactions with proteins like phosphatidylinositol-3-kinase.