https://www.cell.com/cell/pdf/0092-8674(85)90169-2.pdf

A lymphocyte-specific protein-tyrosine kinase gene is rearranged and overexpressed in the murine T cell lymphoma LSTRA

Reversible tyrosine phosphorylation of proteins is a key regulatory mechanism for numerous important aspects of eukaryotic physiology and is catalysed by kinases and phosphatases. Together, cells of the immune system express at least half of the 107 protein tyrosine phosphatase (PTP) genes in the human genome, most of which encode multidomain proteins that contain protein- and phospholipid-interaction domains. Here, we discuss the diverse but specific, and important, roles that PTPs have in immune cells, focusing mainly on T and B cells, and we highlight recent evidence that even subtle alterations in PTPs can cause immune dysfunction and human disease.

Protein tyrosine phosphatases and the immune response.

A human B-lymphoblastoid lambda gt11 expression library was screened using anti-phosphotyrosine antibodies yielding complementary DNAs encoding active tyrosine kinases. The resulting clones were used to obtain the sequence of a novel 984 amino acid transmembrane tyrosine kinase. Analysis of the complementary DNA revealed extracellular immunoglobulin and fibronectin type III domains and the unusual kinase signature sequence KWIAIES; all are characteristic of the axl family of tyrosine kinases. The novel tyrosine kinase was not expressed in normal B- and T-lymphocytes but, unlike axl, was expressed in numerous neoplastic B- and T-cell lines. Transcripts for the novel receptor-like tyrosine kinase were detected in normal peripheral blood monocytes and bone marrow. One alternatively spliced transcript was detected which contained an insert in the membrane proximal region that could encode for a truncated, soluble receptor. Sequence comparison shows that the kinase may be the human protooncogene for the recently isolated chicken retroviral oncogene v-ryk (recently renamed v-eyk), a truncated tyrosine kinase whose expression by retroviral infection produced sarcomas in chickens. The intracellular domain of the human kinase shows 83% similarity and 71% identity to v-ryk. Since the ryk designation has been used to name another tyrosine kinase and an analysis of RNA expression demonstrated that this novel human kinase is expressed in monocytes and tissues of epithelial and reproductive origin, we have designated our novel protooncogene c-mer.

http://cgd.aacrjournals.org/cgi/reprint/5/6/647.pdf

Cloning and mRNA expression analysis of a novel human protooncogene, c-mer.

Publisher Summary This chapter reviews the state of the art in the area of T lymphocyte signal transduction. The chapter presents a critical overview and synthesis of the important findings in the field of T cell activation. The ability to maintain functional antigen-specific T cell clones in long-term culture, and the determination of the primary structure of the T cell antigen–receptor complex and other surface activation molecules have been some of the major advances in T cell immunobiology in recent years. This progress has paved the way to analyze the cascade of biochemical events that constitute the transmembrane signaling machinery. Although this aspect of T cell activation is generally accepted by most researchers in this area, nearly all other biochemical events are poorly understood. These include the mechanisms that couple receptor occupancy to PIP2 hydrolysis, the potential role of other signaling pathways, and the critical cytoplasmic and nuclear events that follow second messenger production. Activation of resting T cells can be initiated by a diverse group of cell surface receptors identified in recent years, originally, by appropriate monoclonal antibodies (mAbs) and, subsequently, by gene cloning and sequencing. The conclusion that such receptors play a role in T cell activation is based on the agonist or antagonist properties of the relevant mAb. The physiological ligands for some, but not all, of these receptors are also identified.

Molecular Events Mediating T Cell Activation

Analysis of pp60c-src protein kinase activity in human tumor cell lines and tissues.

Membrane fractions isolated from mouse and rat spleen expressed substantial tyrosine-specific protein kinase activity. Phosphotyrosine (P-Tyr) accumulation in endogenous membrane substrates was stimulated by vanadate or nonionic detergents. When in vitro phosphorylation was carried out at 0 degree C in the presence of 1 mM Mn2+ and Triton X-100, P-Tyr constituted up to 40-50% of the total phospho amino acid. Polyacrylamide gel electrophoresis showed that membranes from mixed lymphocyte populations have four major P-Tyr-containing proteins. Whereas nonionic detergents were potent stimuli for P-Tyr accumulation in all four substrates, tyrosine phosphorylation of two of these (p61 and p55) was markedly dependent on vanadate. These two substrates were present in membranes from surface Ig-bearing splenic lymphocytes purified by affinity chromatography and Raji, a human B-lymphoblastoid cell line. P-Tyr accumulation in the two other substrates observed in splenocyte membranes (p64 and p58) was much less dependent on vanadate. p64 and p58 were phosphorylated in membranes from mouse thymocytes and human and mouse T-lymphoma cell lines, while p61 and p55 were not. Thus it appears that in both murine and human lymphocytes, p64 and p58 served as T-cell-specific substrates, while p61 and p55 were specifically associated with B lymphocytes. Moreover, these distinct P-Tyr substrate patterns were conserved in some neoplastic cell lines derived from B and T cells.

S C Buessow

Papers

Membranes from T and B lymphocytes have different patterns of tyrosine phosphorylation

Characterization of distinct tyrosine-specific protein kinases in B and T lymphocytes.