Human T-cell leukemia virus type-I-infected T-cell lines scarcely produce p56lck, whether or not they express lck mRNA

Lck Function and Modulation: Immune Cytotoxic Response and Tumor Treatment More Than a Simple Event

Lck, a member of the Src kinase family, is a non-receptor tyrosine kinase involved in immune cell activation, antigen recognition, tumor growth, and cytotoxic response. The enzyme has usually been linked to T lymphocyte activation upon antigen recognition. Lck activation is central to CD4, CD8, and NK activation. However, recently, it has become clearer that activating the enzyme in CD8 cells can be independent of antigen presentation and enhance the cytotoxic response. The role of Lck in NK cytotoxic function has been controversial in a similar fashion as the role of the enzyme in CAR T cells. Inhibiting tyrosine kinases has been a highly successful approach to treating hematologic malignancies. The inhibitors may be useful in treating other tumor types, and they may be useful to prevent cell exhaustion. New, more selective inhibitors have been documented, and they have shown interesting activities not only in tumor growth but in the treatment of autoimmune diseases, asthma, and graft vs. host disease. Drug repurposing and bioinformatics can aid in solving several unsolved issues about the role of Lck in cancer. In summary, the role of Lck in immune response and tumor growth is not a simple event and requires more research.

Mechanisms of T-cell activation by human T-cell lymphotropic virus type I

The interactions between human T-cell lymphotropic virus type I (HTLV-I) and the cellular immune system can be divided into viral interference with functions of the infected host T cell and the subsequent interactions between the infected T cell and the cellular immune system. HTLV-I-mediated activation of the infected host T cell is induced primarily by the viral protein Tax, which influences transcriptional activation, signal transduction pathways, cell cycle control, and apoptosis. These properties of Tax may well explain the ability of HTLV-I to immortalize T cells. It is not clear, though, how HTLV-I induces T-cell transformation (interleukin-2 [IL-2] independence). Recent evidence suggests that Tax may promote the G1- to S-phase transition, although this may involve additional proteins. A role for other viral proteins that may constitutively activate the IL-2 receptor pathway has also been suggested. By virtue of their activated state, HTLV-I-infected T cells can nonspecifically activate resting, uninfected T cells via virus-mediated upregulation of adhesion molecules. This may favor viral dissemination. Moreover, the induction of a remarkably high frequency of antiviral CD8(+) T cells does not appear to eliminate the infection. Indeed, individuals with a high frequency of virus-specific CD8(+) T cells have a high viral load, indicating a state of chronic immune system stimulation. Thus, while an activated immune system is needed to eradicate the infection, the spread of the HTLV-I is also accelerated under these conditions. A detailed knowledge of the molecular interactions between virus-specific CD8(+) T cells and immunodominant viral epitopes holds promise for the development of specific antiviral therapy.

Cellular transformation by human T-cell leukemia virus type I

Human T-cell leukemia virus type I (HTLV-I) is an oncogenic retrovirus that was isolated in 1980 from a patient with adult T-cell leukemia. From the numerous experiments using infected patient T-cells, transgenic mice and tissue culture transformation assays, the Tax protein has been determined to be the transforming component of HTLV-I. Tax-mediated transformation is linked to its ability to transcriptionally regulate the expression of cellular genes involved in growth and proliferation. Ultimately, unregulated and continued activation of these important growth modulating genes by Tax leads to transformation.

Expression of CD4-like structure on murine egg vitelline membrane and its signal transductive roles through p56lck in fertilization

Expression of CD4-like molecule on vitelline membrane of murine eggs was demonstrated by indirect immunofluorescence (IIF) test and immunoprecipitation corresponding to the expression of major histocompatibility complex (MHC) class II molecule on murine sperm detected by immunoblotting. This molecule showed slightly larger size than that of the authentic CD4 molecule from T-cells on SDS-PAGE. This molecule was suggested to bind to MHC class II structure on sperm during fertilization because anti-CD4 monoclonal antibody (mAb) blocked in vitro fertilization (IVF). In addition, src-related tyrosine protein kinase (p56lck) was demonstrated in the inner vitelline membrane of eggs by means of IIF with anti-p56lck mAb and immune-complex kinase assay. This molecule was suggested to be associated with CD4-like molecule.

Accumulation of p60lck in HTLV-I-transformed T cell lines detected by an anti-lck monoclonal antibody, MOL 171

The lck gene encodes a protein tyrosine kinase of nonreceptor type, p56lck, whose expression occurs almost exclusively in T lymphocytes. MOL 171, an anti-p56lck monoclonal antibody, was produced by using a 25-amino-acid synthetic polypeptide as the antigen, its structure corresponding to the N-terminal region deduced from the lck cDNA sequence. Immunoblot analysis with MOL 171 showed the accumulation of 60 kD form of Lck protein, p60lck, and the decrease of p56lck in human T cell leukemia virus type I (HTLV-I)-transformed T cell lines. Another anti-Lck monoclonal antibody, MOL 294, raised by using a synthetic peptide corresponding to the C-terminal region deduced from the lck cDNA sequence, also detected the accumulation of p60lck in those HTLV-I-transformed T cell lines. The appearance of p60lck with the decrease of p56lck in normal T lymphocytes after stimulation suggested the origin of p60lck in HTLV-I-transformed T cells.

Differential expression of two lck transcripts directed from the distinct promoters in HTLV-I+ and HTLV-I- T-cells

The lck gene encodes a lymphocyte-specific tyrosine protein kinase, p56lck, the expression of which is almost exclusive in T-cells. The expression of lck in human T-cell leukemia virus type I (HTLV-I)-transformed T-cell lines is closely associated with interleukin-2 (IL-2) dependence for their growth. That is, IL-2-dependent HTLV-I-transformed cell lines contain the lck message abundantly as HTLV-I-negative T-cell lines, whereas IL-2-independent HTLV-I-transformed cell lines express either no or little lck mRNA, although they are derived from T-cells. The lck gene contains 2 distinct promoters which direct 2 types of lck transcript with different 5' untranslated regions. In this study, we show that HTLV-I-transformed IL-2-dependent T-cell lines contain the upstream promoter-initiated lck transcript exclusively, in contrast to HTLV-I-negative transformed T-cell lines which express the down-stream promoter- as well as the upstream promoter-initiated lck transcript. In addition, lck mRNA disappears transiently in IL-2-dependent HTLV-I-transformed T-cell lines after stimulation for T-cell activation, which is also observed in peripheral blood T lymphocytes. These results indicate that the disappearance of lck mRNA in HTLV-I-transformed, IL-2-independent cell lines is caused by a mechanism which down-regulates the upstream promoter-initiated lck transcript and this IL-2-independent state may represent a further "activated" condition of the IL-2-dependent state by the stimulation which mediates T-cell activation.