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Multiple tyrosine protein kinases structurally related to p56 lck are down-regulated following mitogenic stimulation
B S Hall1, A V Hoffbrand, R G Wickremasinghe
1Department of Haematology, Royal Free Hospital and School of Medicine, London, UK.
Abstract:
p56 lck is a well-characterized tyrosine protein kinase (TPK) which is thought to play a role in mitogenic signal transduction in T lymphocytes. Immunoblot analysis of human lymphocyte proteins using an antiserum cross-reactive with phosphotyrosine resulted in the detection of a 55-60 kDa protein band (presumably p56 lck) as well as several additional phosphotyrosyl proteins in lymphocyte extracts. All of these phosphotyrosyl proteins were down-regulated following mitotic stimulation. Autophosphorylation of lymphocyte microsomal fractions in the presence of [gamma-32P] ATP resulted in the labelling of p56 lck as well as other proteins of different molecular weights. Analysis of these labelled proteins by tryptic digestion resulted in strikingly similar peptide maps. The data suggest that lymphocytes may contain a family of TPKs structurally related to p56 lck. The down-regulation of the putative TPKs following mitogenic stimulation of lymphocytes with phytohaemagglutinin suggests that this family of TPKs may participate in mitotic signalling events, followed by their down-regulation.
Insights
p56 lck, a tyrosine protein kinase (TPK), and related TPKs in lymphocytes are down-regulated after mitotic stimulation. This suggests their role in T-cell signaling pathways.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- p56 lck is a known tyrosine protein kinase (TPK) involved in T-lymphocyte mitogenic signal transduction.
- Phosphotyrosyl proteins, including p56 lck, are present in human lymphocyte extracts.
Purpose of the Study:
- To investigate the role of p56 lck and related tyrosine protein kinases in T-lymphocyte activation.
- To identify phosphotyrosyl proteins in lymphocytes and their regulation during mitogenic stimulation.
Main Methods:
- Immunoblot analysis using anti-phosphotyrosine antiserum.
- Autophosphorylation assays with [gamma-32P] ATP on lymphocyte microsomal fractions.
- Tryptic peptide mapping of labeled proteins.
Main Results:
- Detection of a 55-60 kDa phosphotyrosyl protein band (putative p56 lck) and other related phosphotyrosyl proteins.
- Down-regulation of these phosphotyrosyl proteins upon mitogenic stimulation.
- Similar peptide maps for p56 lck and other identified TPKs, suggesting structural relatedness.
Conclusions:
- Lymphocytes may possess a family of TPKs structurally related to p56 lck.
- The observed down-regulation of these TPKs during mitogenic stimulation indicates their potential involvement in T-cell mitotic signaling.