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A Raf-1-related p110 polypeptide associates with the CD4-p56lck complex in T cells
1Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, Massachusetts.
Abstract:
The CD4 and CD8 antigens on T cells have been shown to associate with the Src family member p56lck and a GTP-binding protein, p32. The identification of receptor interactions with intracellular mediators is essential in the elucidation of downstream signals mediated by engagement of these receptor complexes. In this study, we report the detection of an additional 110-kDa polypeptide (p110) associated with the CD4-p56lck complex in human peripheral blood T lymphocytes and leukemic T-cell lines. p110 bound preferentially to CD4-p56lck as an assembled complex and poorly, if at all, to the individual components. p110 was recognized directly by an antiserum to the C-terminal region of the serine/threonine kinase Raf-1 and is related to a p110 polypeptide detected in anti-Raf-1 immunoprecipitates. Despite its association with the CD4-p56lck complex, p110 was found to be phosphorylated predominantly on serine residues. Furthermore, phorbol ester treatment of cells resulted in a transient increase in the detection of p110 associated with CD4-p56lck, concomitant with the modulation of CD4-p56lck from the cell surface. This Raf-1-related p110 is therefore likely to play a role in signals generated from the CD4-p56lck complex. p110 may serve as a bridge between the CD4-p56lck complex and the serine/threonine kinase pathways of T-cell activation.
Insights
A novel 110-kDa protein (p110) associates with the CD4-p56lck complex in T cells, potentially bridging it to Raf-1 kinase pathways. This finding offers new insights into T-cell activation signaling.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- T cell receptor complexes, including CD4 and CD8, interact with intracellular mediators like p56lck and p32.
- Understanding these interactions is crucial for elucidating downstream signaling pathways.
Purpose of the Study:
- To identify novel polypeptides associated with the CD4-p56lck complex in human T lymphocytes.
- To investigate the nature and function of a newly detected 110-kDa polypeptide (p110).
Main Methods:
- Co-immunoprecipitation assays using human peripheral blood T lymphocytes and T-cell lines.
- Western blot analysis with specific antisera, including one against Raf-1 kinase.
- Analysis of p110 phosphorylation and its association with CD4-p56lck upon phorbol ester treatment.
Main Results:
- A 110-kDa polypeptide (p110) was detected associated with the CD4-p56lck complex.
- p110 preferentially bound to the assembled CD4-p56lck complex, not individual components.
- p110 is related to Raf-1 kinase and phosphorylated on serine residues.
- Phorbol ester treatment increased p110 association with CD4-p56lck and modulated CD4-p56lck surface expression.
Conclusions:
- The Raf-1-related p110 is a novel component of the CD4-p56lck signaling complex.
- p110 likely plays a role in signal transduction from the CD4-p56lck complex.
- p110 may act as a molecular bridge connecting the CD4-p56lck complex to serine/threonine kinase pathways involved in T-cell activation.