Transcriptional activation of lck by retrovirus promoter insertion between two lymphoid-specific promoters

The LCK-14-3-3ζ-TRPM8 axis regulates TRPM8 function/assembly and promotes pancreatic cancer malignancy

Transient receptor potential melastatin 8 (TRPM8) functions as a Ca2+-permeable channel in the plasma membrane (PM). Dysfunction of TRPM8 is associated with human pancreatic cancer and several other diseases in clinical patients, but the underlying mechanisms are unclear. Here, we found that lymphocyte-specific protein tyrosine kinase (LCK) directly interacts with TRPM8 and potentiates TRPM8 phosphorylation at Y1022. LCK positively regulated channel function characterized by increased TRPM8 current densities by enhancing TRPM8 multimerization. Furthermore, 14-3-3ζ interacted with TRPM8 and positively modulated channel multimerization. LCK significantly enhanced the binding of 14-3-3ζ and TRPM8, whereas mutant TRPM8-Y1022F impaired TRPM8 multimerization and the binding of TRPM8 and 14-3-3ζ. Knockdown of 14-3-3ζ impaired the regulation of TRPM8 multimerization by LCK. In addition, TRPM8 phosphotyrosine at Y1022 feedback regulated LCK activity by inhibiting Tyr505 phosphorylation and modulating LCK ubiquitination. Finally, we revealed the importance of TRPM8 phosphorylation at Y1022 in the proliferation, migration, and tumorigenesis of pancreatic cancer cells. Our findings demonstrate that the LCK-14-3-3ζ-TRPM8 axis for regulates TRPM8 assembly, channel function, and LCK activity and maybe provide potential therapeutic targets for pancreatic cancer.

Insertional activation of STAT3 and LCK by HIV-1 proviruses in T cell lymphomas

Retroviruses cause cancers in animals by integrating in or near oncogenes. Although HIV-1 infection increases the risk of cancer, most of the risk is associated with immunodeficiency and coinfection by oncogenic virus (Epstein-Barr virus, Kaposi sarcoma herpesvirus, and human papillomavirus). HIV-1 proviruses integrated in some oncogenes cause clonal expansion of infected T cells in vivo; however, the infected cells are not transformed, and it is generally believed that HIV-1 does not cause cancer directly. We show that HIV-1 proviruses integrated in the first introns of signal transducer and activator of transcription 3 (STAT3) and lymphocyte-specific protein tyrosine kinase (LCK) can play an important role in the development of T cell lymphomas. The development of these cancers appears to be a multistep process involving additional nonviral mutations, which could help explain why T cell lymphomas are rare in persons with HIV-1 infection.

Comparative analysis of gene expression mechanisms between group IA and IB phospholipase A2 genes from sea snake Laticauda semifasciata

Phospholipase A(2) (PLA(2)) genes expressed in the venom glands of the sea snake, Laticauda semifasciata, were investigated. Both mRNAs, encoding group IA (without a pancreatic loop) and group IB (with pancreatic loop), were detected from venom glands by Northern blot hybridization analysis and RT-PCR. The results of quantitative PCR analysis indicated that the expression amount of group IA genes was around 100-300 times greater than that of group IB genes. Sequence analysis of 5'-upstream regions and a reporter gene assay of the genes (groups IA and IB) previously cloned showed that the functional sequence (411 bp) was inserted in the 5'-flanking region of the group IA PLA(2) genes. It seemed that the contribution of the inserted sequence to the amount of transcribed mRNAs was greater than that of number of genes present in the genome. Comparative analysis of the 5'-flanking sequences from several snake genes encoding toxic PLA(2)s revealed that this sequence was probably inserted into an ancestral gene of PLA(2) with a pancreatic loop. After the duplication of the gene, which contained the inserted sequence, the PLA(2) gene without a pancreatic loop evolved from one of the duplicate genes. This inserted sequence might determine the future of the genes expressed in the venom glands.

Large-scale identification of disease genes involved in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of diseases in which chromosomal aberrations, small insertions or deletions, or point mutations in certain genes have profound consequences for prognosis. However, the majority of AML patients present without currently known genetic defects. Retroviral insertion mutagenesis in mice has become a powerful tool for identifying new disease genes involved in the pathogenesis of leukemia and lymphoma. Here we have used the Graffi-1.4 strain of murine leukemia virus, which causes predominantly AML, in a screen to identify novel genes involved in the pathogenesis of this disease. We report 79 candidate disease genes in common integration sites (CISs) and 15 genes whose family members previously were found to be affected in other studies. The majority of the identified sequences (60%) were not found in lymphomas and monocytic leukemias in previous screens, suggesting a specific involvement in AML. Although most of the virus integrations occurred in or near the 5' or 3' ends of the genes, suggesting deregulation of gene expression as a consequence of virus integration, 18 CISs were located exclusively within the genes, conceivably causing gene disruption.

Conserved regulation of the lymphocyte-specific expression of lck in the Fugu and mammals

The lck gene encodes a lymphocyte-specific protein-tyrosine kinase that is implicated in T cell maturation and signaling. In mammals, the transcription of the lck gene is regulated by two independent promoters, the proximal promoter, which is active in thymocytes, and the distal promoter, which dominates in mature T cells. In the human and mouse lck gene loci, the two promoter elements are separated by at least 40 kb and 10 kb, respectively. In this study, we have cloned and sequenced 60 kb from the pufferfish (Fugu rubripes) lck locus. The promoter region of the Fugu lck spans only 4.2 kb and contains a proximal and a distal promoter in the 2.3-kb region adjacent to the coding sequence. By generating transgenic mice, we have demonstrated that the compact promoter of the Fugu lck contains regulatory elements that direct expression to lymphoid organs of mice. We were able to localize the regulatory elements to a short region of 830 bp without losing specificity to cultured human T cell line. These results show that the basic mechanisms that mediate lymphocyte-specific expression are conserved between teleosts and mammals. The short promoter of the Fugu lck isolated by us offers a powerful tool for labeling T cells, targeting expression, and manipulating T cell activity in fishes as well as in mammals.

Identification and characterization of a transcriptional regulator for the lck proximal promoter

The lck gene encodes a protein-tyrosine kinase that plays a key role in signaling mediated through T cell receptor (TCR) and pre-TCR complexes. Transcription of the lck gene is regulated by two independent promoter elements: the proximal and distal promoters. Previous studies employing transgenic mice demonstrated that the sequence between -584 and -240 from the transcription start site in the mouse lck proximal promoter is required for its tissue-specific expression in the thymus. In this study, we demonstrate that a Krüppel-like zinc finger protein, mtbeta (BFCOL1, BERF-1, ZBP-89, ZNF148), previously cloned as a protein that binds to the CD3delta gene enhancer, binds to the -365 to -328 region of the lck proximal promoter. mtbeta is ubiquitously expressed in various cell lines and mouse tissues. Overexpressed mtbeta is more active in T-lineage cells than B-lineage cells for transactivating an artificial promoter consisting of the mtbeta binding site and a TATA box. Activity of the lck proximal promoter was significantly impaired by mutating the mtbeta binding site or by reducing mtbeta protein expression level by using antisense mRNA. Our results indicate that mtbeta activity is regulated in a tissue-specific manner and that mtbeta is a critical transactivator for the lck proximal promoter.

Detection of p56(lck) kinase activity using scintillation proximity assay in 384-well format and imaging proximity assay in 384- and 1536-well format

p56(lck) is a lymphocyte-specific tyrosine kinase that plays an important role in both T-cell maturation and activation. We have developed a homogeneous assay in which p56(lck) catalyzes the transfer of the gamma-phosphate group from [gamma-(33)P]ATP to a biotinylated peptide substrate. The labeled peptide is then captured on a streptavidin-coated scintillation proximity assay (SPA) bead or imaging proximity bead. The SPA is counted in a microplate scintillation counter and the imaging proximity assay is counted in a charge-coupled device-based imaging system called LEADseekertrade mark, recently launched as a homogeneous imaging system by Amersham Pharmacia Biotech. We show, via time-dependence assays and inhibitor studies, that this assay can be performed in 1536-well microplate format using imaging proximity as the method of detection. The results compare favorably with the same assay performed in 384-well microplate format using both SPA and imaging proximity as the detection methods. From this study, we conclude that a kinase assay can be performed in 384- and 1536-well format using imaging as the detection method, with significant time savings over standard scintillation counting. In addition, we show cost saving advantages of 1536- over 384-well format in terms of reagent usage, higher throughput, and waste disposal.

Dysregulation of the protein tyrosine kinase LCK in lymphoproliferative disorders and in other neoplasias

Initially identified as a T-cell specific member of the Src family of protein tyrosine kinases, Lck has become the object of intensive investigations which have revealed a key role for this kinase in the central processes controlling T-cell development, activation, proliferation and survival. Experimental evidence of the oncogenic potential of Lck, together with the identification of defects in the regulation of Lck expression or activity in T-cell leukemias, suggests that dysregulation of Lck might play a role in neoplastic transformation. Here we review the data documenting a potential role for this kinase in the initiation and maintenance of the transformed state in human cancers.

Regulation of Src-family protein tyrosine kinase transcription during lymphocyte ontogeny

The distribution and quantity of cellular signaling elements influence response patterns to a variety of stimuli. As protein tyrosine phosphorylation is a requisite event induced by a majority of surface receptors, and protein tyrosine kinases of the src-family (src-PTKs) act as proximal transducers for many hematopoietic receptors, we have designed a quantitative RT-PCR assay to measure src-family PTK expression during critical stages of lymphocyte ontogeny. With this assay we demonstrate that the distal promoter element regulating expression of lck, a src-PTK essential for T-cell development and activation, is similarly regulated during ontogeny of T and B cells. However, lck transcript abundance is drastically reduced in B lineage cells, suggesting that transcriptional elements influencing lck promoter activity are modulated in these cells. Moreover, although transcripts encoding the src-PTK fyn accumulate at 0.1% of lck mRNA levels in thymocytes, diminished activity of the lck distal promoter in the B-cell background brings lck and fyn transcript levels to near equivalence in this population. Importantly, transcripts arising from the lck distal promoter element and the fyn locus are similarly upregulated during developmental transitions associated with antigen-receptor expression in both B and T cells. These findings suggest that although the magnitude of lck and fyn expression is differentially regulated in B and T cells, expression at these loci is similarly developmentally programmed during ontogeny of both lymphocyte lineages.

The development of novel and selective p56lck tyrosine kinase inhibitors

Early T-cell receptor mediated signal transduction involves the activation of several tyrosine protein kinases. One of these tyrosine kinases, p56lck, is expressed primarily in T-cells and Natural Killer (NK) cells and has been shown to be critical for their proliferative and effector functions. Indandiones have been identified as a potent and selective chemical class that inhibits p56lck.

A homogeneous, fluorescence polarization assay for src-family tyrosine kinases

A nonradioactive, simple, sensitive fluorescence polarization assay was developed to assay protein tyrosine kinase activity. This assay involves incubation of a fluorescenylated peptide substrate with the kinase, ATP, and anti-phosphotyrosine antibody. The phosphorylated peptide product is immunocomplexed with the anti-phosphotyrosine antibody resulting in an increase in the polarization signal as measured in a fluorescence polarization analyzer. Among several anti-phosphotyrosine antibodies examined, monoclonal antibody PY54 was found to give the best polarization signal with the test peptide. For validation of the fluorescence polarization assay, Lck activity was compared with a 32PO4 transfer assay. In both the fluorescence polarization and 32PO4 transfer assays, Lck activity showed a similar dependence on ATP, Lck enzyme, and peptide substrate concentrations. Both assays gave similar inhibition constants with a known tyrosine kinase inhibitor staurosporine and the Lck inhibitor, 4-amino-5-(methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine. These results show that the fluorescence polarization assay can detect inhibitors and is comparable to the 32PO4 transfer assay. The fluorescence polarization method is advantageous compared to the 32PO4 transfer assay or ELISA or DELFIA because it is a one-step assay that does not involve several washings, liquid transfer, and sample preparation steps. It has the added advantage of using nonisotopic substrates. The fluorescence polarization assay thus is environmentally safe and minimizes handling problems. The homogeneous nature of the assay makes it readily adaptable to high-throughput screening for small-molecule drug discovery.

Expression of p56lck in B-cell neoplasias

The protooncogene p56lck is considered to participate in malignant transformation of lymphoid cells. In order to evaluate the role of this tyrosine kinase in B cell neoplasias, we investigated the expression of p56lck by Western blot analysis. In 12/16 Burkitt's lymphoma derived cell lines, 3/3 lymphoblastoid cell lines, 1/6 Hodgkin's disease derived cell lines, and 10/10 freshly isolated chronic lymphocytic leukemia cells constitutive expression of the protein was detected. Protein tyrosine kinase assays detected a catalytic active form of p56lck in all p56lck expressing samples. Stimulation experiments of the different cell lines and primary tumour cells by the phorbol ester TPA and the B-cell specific stimulation with SAC/anti-IgM respectively indicated a change of the expression level in comparison with the unstimulated cells and, a higher molecular weight species of the protein tyrosine kinase p56lck was observed. This was probably due to hyperphosphorylation of p56lck. No correlation between an infection with the Epstein-Barr virus and the expression of p56lck was found in the cell lines used and in primary tumour cells. Inhibition of p56lck activity by the specific inhibitor 4-amino-6-hydroxyflavone revealed a decrease of proliferation of the T-cell line Jurkat, but not of the Burkitt's lymphoma cell lines. In the analysed cell lines we found a reduction of the kinase activity of p56lck of approximately 70%. These results suggest that lck may contribute to the maintenance of the transformation of the analysed B cell neoplasias but that lck does not support a model for an initial event in B cell transformation.

Discovery of a novel, potent, and Src family-selective tyrosine kinase inhibitor. Study of Lck- and FynT-dependent T cell activation

Here, we have studied the activity of a novel protein-tyrosine kinase inhibitor that is selective for the Src family of tyrosine kinases. We have focused our study on the effects of this compound on T cell receptor-induced T cell activation, a process dependent on the activity of the Src kinases Lck and FynT. This compound is a nanomolar inhibitor of Lck and FynT, inhibits anti-CD3-induced protein-tyrosine kinase activity in T cells, demonstrates selectivity for Lck and FynT over ZAP-70, and preferentially inhibits T cell receptor-dependent anti-CD3-induced T cell proliferation over non-T cell receptor-dependent phorbol 12-myristate 13-acetate/interleukin-2 (IL-2)-induced T cell proliferation. Interestingly, this compound selectively inhibits the induction of the IL-2 gene, but not the granulocyte-macrophage colony-stimulating factor or IL-2 receptor genes. This compound offers a useful new tool for examining the role of the Lck and FynT tyrosine kinases versus ZAP-70 in T cell activation as well as the role of other Src family kinases in receptor function.

Lck-dependent tyrosyl phosphorylation of the phosphotyrosine phosphatase SH-PTP1 in murine T cells

The phosphorylation and dephosphorylation of proteins on tyrosyl residues are key regulatory mechanisms in T-cell signal transduction and are controlled by the opposing activities of protein tyrosine kinases and phosphotyrosyl phosphatases (PTPs). In T cells, several nontransmembrane protein tyrosine kinases are associated with receptors; for example, Lck is bound to the coreceptors CD4 and CD8 and becomes activated upon their stimulation. In comparison, little is known about the role of nontransmembrane PTPs in early T-cell signaling. SH-PTP1 (PTP1C, HCP, SHP) is a nontransmembrane PTP expressed primarily in hematopoietic cells, including T cells. We have found that SH-PTP1 is basally phosphorylated on serine in resting T cells. Upon stimulation of CD4 or CD8 either in a T-cell hybridoma cell line or in primary thymocytes, SH-PTP1 becomes tyrosyl phosphorylated. Moreover, SH-PTP1 is constitutively phosphorylated on tyrosine in the Lck-overexpressing lymphoma cell line LSTRA. SH-PTP1 is also a good substrate for recombinant Lck in vitro. Comparisons of the tryptic phosphopeptide maps of wild-type SH-PTP1 and deletion and point mutations establish that the two sites (Y-536 and Y-564) which are directly phosphorylated by Lck in vitro are also phosphorylated in vivo in LSTRA cells. One of these sites (Y-564) is phosphorylated in T cells in response to Lck activation. We conclude that SH-PTP1 undergoes Lck-dependent tyrosyl phosphorylation in T cells and likely plays a role in early T-cell signaling.

Lck-dependent tyrosyl phosphorylation of the phosphotyrosine phosphatase SH-PTP1 in murine T cells

The phosphorylation and dephosphorylation of proteins on tyrosyl residues are key regulatory mechanisms in T-cell signal transduction and are controlled by the opposing activities of protein tyrosine kinases and phosphotyrosyl phosphatases (PTPs). In T cells, several nontransmembrane protein tyrosine kinases are associated with receptors; for example, Lck is bound to the coreceptors CD4 and CD8 and becomes activated upon their stimulation. In comparison, little is known about the role of nontransmembrane PTPs in early T-cell signaling. SH-PTP1 (PTP1C, HCP, SHP) is a nontransmembrane PTP expressed primarily in hematopoietic cells, including T cells. We have found that SH-PTP1 is basally phosphorylated on serine in resting T cells. Upon stimulation of CD4 or CD8 either in a T-cell hybridoma cell line or in primary thymocytes, SH-PTP1 becomes tyrosyl phosphorylated. Moreover, SH-PTP1 is constitutively phosphorylated on tyrosine in the Lck-overexpressing lymphoma cell line LSTRA. SH-PTP1 is also a good substrate for recombinant Lck in vitro. Comparisons of the tryptic phosphopeptide maps of wild-type SH-PTP1 and deletion and point mutations establish that the two sites (Y-536 and Y-564) which are directly phosphorylated by Lck in vitro are also phosphorylated in vivo in LSTRA cells. One of these sites (Y-564) is phosphorylated in T cells in response to Lck activation. We conclude that SH-PTP1 undergoes Lck-dependent tyrosyl phosphorylation in T cells and likely plays a role in early T-cell signaling.

tkl is the avian homolog of the mammalian lck tyrosine protein kinase gene

We have tested the possibility that tkl, a partially characterized avian tyrosine protein kinase gene, is the chicken homolog of lck, a lymphocyte-specific mammalian gene. Using polymerase chain reactions, we have cloned sequences encoding the previously unidentified amino terminus of the tkl gene product. The newly defined unique domain of Tkl displayed significant identity (68%) to the equivalent region of the mammalian lck gene product, p56lck. This identity included a glycine residue at position 2 (present in all Scr-related tyrosine protein kinases) and a cysteine motif at positions 20 and 23, which allows binding of p56lck to CD4 and CD8 in mammalian T lymphocytes. A specific RNase protection assay revealed that, in contrast to a previous report (K. Strebhardt, J. I. Mullins, C. Bruck, and H. Rübsamen-Waigmann, Proc. Natl. Acad. Sci. USA 84:8778-8782, 1987), tkl expression is restricted to the lymphoid tissues thymus and spleen. Moreover, the absence of tkl transcripts in the bursa of Fabricius suggested that this gene is expressed in avian T lymphocytes but not in B lymphocytes. A polyclonal rabbit antiserum raised against the unique domain of Tkl recognized a 56-kDa polypeptide with associated protein kinase activity from avian thymus-derived cells. Additional studies showed that p56tkl is structurally similar to mammalian p56lck and that it is physically associated with the avian CD4 and CD8 T-cell surface antigens. It was also determined that tkl transcripts have one major type of 5' untranslated region (UTR), which differs greatly from the two known 5' UTRs of mammalian lck mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

tkl is the avian homolog of the mammalian lck tyrosine protein kinase gene

We have tested the possibility that tkl, a partially characterized avian tyrosine protein kinase gene, is the chicken homolog of lck, a lymphocyte-specific mammalian gene. Using polymerase chain reactions, we have cloned sequences encoding the previously unidentified amino terminus of the tkl gene product. The newly defined unique domain of Tkl displayed significant identity (68%) to the equivalent region of the mammalian lck gene product, p56lck. This identity included a glycine residue at position 2 (present in all Scr-related tyrosine protein kinases) and a cysteine motif at positions 20 and 23, which allows binding of p56lck to CD4 and CD8 in mammalian T lymphocytes. A specific RNase protection assay revealed that, in contrast to a previous report (K. Strebhardt, J. I. Mullins, C. Bruck, and H. Rübsamen-Waigmann, Proc. Natl. Acad. Sci. USA 84:8778-8782, 1987), tkl expression is restricted to the lymphoid tissues thymus and spleen. Moreover, the absence of tkl transcripts in the bursa of Fabricius suggested that this gene is expressed in avian T lymphocytes but not in B lymphocytes. A polyclonal rabbit antiserum raised against the unique domain of Tkl recognized a 56-kDa polypeptide with associated protein kinase activity from avian thymus-derived cells. Additional studies showed that p56tkl is structurally similar to mammalian p56lck and that it is physically associated with the avian CD4 and CD8 T-cell surface antigens. It was also determined that tkl transcripts have one major type of 5' untranslated region (UTR), which differs greatly from the two known 5' UTRs of mammalian lck mRNAs.(ABSTRACT TRUNCATED AT 250 WORDS)

The LCK gene is involved in the t(1;7)(p34;q34) in the T-cell acute lymphoblastic leukemia derived cell line, HSB-2

HSB-2 is a cell line derived from a patient who had T-cell acute lymphoblastic leukemia (T-cell ALL) with a t(1;7)(p34;q34). We used a genomic probe from the T-cell receptor beta (TCR beta) locus (7q34) to identify DNA rearrangements in HSB-2. Two rearranged BglII DNA fragments were cloned, and one of these clones was shown to contain the translocation breakpoint on the derivative chromosome I [der(I)]. We used a probe derived from this clone to isolate an unrearranged phage clone encompassing the breakpoint at Ip34. The restriction map of this clone was compared to the published maps of known protooncogenes located at Ip32-34. By restriction mapping, Southern blot analysis, and DNA sequencing we showed that the translocation breakpoint on chromosome I is located within the first intron of the LCK gene. The LCK gene codes for p56lck, a member of the SRC family of cytoplasmic tyrosine protein kinases. There are two classes of LCK transcripts (type I and type II), each expressed from a distinct promoter, and each having a unique 5' untranslated region (UTR); the protein coding regions of the two classes are identical. The breakpoint in the t(1;7) separates the two LCK promoters and juxtaposes the constant region of the TCR beta locus with the proximal promoter and with the protein-coding region of the LCK gene on the der(I) chromosome.

Differential expression of two classes of lck transcripts upon phorbol ester treatment of human leukemic T cells

The human lymphocyte-specific tyrosine kinase gene, lck, is transcribed from two distinct promoters, resulting in two classes of transcripts (type I and II) differing in their 5' untranslated regions. The steady-state levels of the type I and II lck transcripts were measured in a variety of lymphoid and non-lymphoid human tumor cell lines by S1 nuclease mapping and by a sensitive assay system using the polymerase chain reaction. Human thymocytes and all the leukemic T cell lines tested express both type I and II lck transcripts, albeit at different relative levels. Peripheral blood T cells express mainly type II lck transcripts, whereas two colonic carcinoma lines, COLO 201 and COLO 205, express exclusively type I lck transcripts. Treatment of the leukemic T cell lines, P30/OKUBO and Jurkat, by the phorbol esters tetradecanoylphorbol acetate (TPA) or phorbol dibutyrate (PDB) results in the down-regulation of the type I, and the up-regulation of the type II, lck transcript levels. The effect of PDB on the in vitro differentiation of Jurkat cells, and the expression of lck transcripts, is reversible. The modulation of lck transcript levels in TPA-treated Jurkat cells is not due to differential RNA stability, suggesting that the two lck promoters are utilized differentially during T cell differentiation. The leukemic T cell line, Jurkat, may thus serve as a model for the elucidation of molecular mechanisms that regulate lck transcription and T cell differentiation.

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.

Delayed thymocyte development induced by augmented expression of p56lck

Accumulating evidence supports the contention that CD4 and CD8 receptor molecules play a critical signaling role during thymocyte development. The lymphocyte-specific protein tyrosine kinase (p56lck), by virtue of its physical association with these surface components, provides a likely candidate for the biochemical signal transducing element required for these effects. To investigate the function of p56lck in T lymphocytes, transgenic mice were produced that carry either the wild-type lck gene or a mutated lck gene encoding a constitutively activated form of p56lck (p56lckF505). Both transgenes were expressed in thymocytes under the control of the lck proximal promoter element. A large set of founder animals was obtained in which steady-state accumulation of lck transgene mRNA directly correlated with transgene copy number, suggesting that this transgene contains a dominant control region. Progeny of these founders exhibited a transgene-dependent dose-related decrease in the production of thymocytes bearing functional antigen receptors. This effect was strictly dependent on p56lck activity, in that both wild-type and mutated versions of the genes induced similar effects with differing efficiencies. Remarkably, even a twofold increase in p56lck abundance was sufficient to substantially disrupt the appearance of functional thymocytes. These results indicate that thymocyte maturation is regulated in part by signals derived from p56lck.

Hematopoietic cells express two forms of lyn kinase differing by 21 amino acids in the amino terminus

cDNAs for the murine lyn protein tyrosine kinase gene were cloned from mouse bone marrow-derived monocytic cells. Comparison of the human and murine genes demonstrated a 94% homology in peptide sequence. Comparable to the human gene, murine lyn was found to be expressed in myeloid and B-lymphoid lineage cells. During the cloning, two types of cDNAs were obtained that differed by the presence (lynA) or absence (lynB) of 63 bp within the amino-terminal coding region of the gene. The genomic structure of the murine lyn gene demonstrates that the two types of lyn transcripts are derived from alternative splicing utilizing an internal splice donor site. Transcripts for both forms were found to be expressed in myeloid cells. lyn-specific antisera detected comparable levels of proteins of 56 and 53 kDa in hematopoietic cells. these 56- and 53-kDa proteins comigrated with proteins produced by in vitro translation or in vivo expression of the lynA and lynB cDNAs, respectively. The two forms had comparable in vitro kinase activities in immunoprecipitates and showed similar peptide patterns, with partial V8 digestion of the in vitro-phosphorylated proteins. The potential significance of the two lyn proteins is discussed.

Hematopoietic cells express two forms of lyn kinase differing by 21 amino acids in the amino terminus

cDNAs for the murine lyn protein tyrosine kinase gene were cloned from mouse bone marrow-derived monocytic cells. Comparison of the human and murine genes demonstrated a 94% homology in peptide sequence. Comparable to the human gene, murine lyn was found to be expressed in myeloid and B-lymphoid lineage cells. During the cloning, two types of cDNAs were obtained that differed by the presence (lynA) or absence (lynB) of 63 bp within the amino-terminal coding region of the gene. The genomic structure of the murine lyn gene demonstrates that the two types of lyn transcripts are derived from alternative splicing utilizing an internal splice donor site. Transcripts for both forms were found to be expressed in myeloid cells. lyn-specific antisera detected comparable levels of proteins of 56 and 53 kDa in hematopoietic cells. these 56- and 53-kDa proteins comigrated with proteins produced by in vitro translation or in vivo expression of the lynA and lynB cDNAs, respectively. The two forms had comparable in vitro kinase activities in immunoprecipitates and showed similar peptide patterns, with partial V8 digestion of the in vitro-phosphorylated proteins. The potential significance of the two lyn proteins is discussed.

Thymic tumorigenesis induced by overexpression of p56lck

The lck gene encodes a membrane-associated protein tyrosine kinase (p56lck) that is believed to participate in lymphocyte-specific signal transduction pathways. To investigate the function of this molecule, transgenic mice were generated carrying the wild-type lck gene or a mutated lck gene encoding a constitutively activated form of p56lck (p56lckF505). Transgene expression in thymocytes was achieved in each case using the lck proximal promoter element. Mice expressing high levels of either p56lckF505 or p56lckY505 reproducibly developed thymic tumors. The sensitivity of thymocytes to p56lck-induced transformation suggests that disturbances in lck expression may contribute to the pathogenesis of some human neoplastic diseases.

Safety issues related to retroviral-mediated gene transfer in humans

The first three approved human clinical trials utilizing retroviral-mediated gene transfer are now underway. While this technology holds great promise for the study and treatment of human disease, it also poses a number of safety concerns. In evaluating clinical protocols, potential complications and the likelihood of their occurrence are estimated by review committees so that a risk/benefit assessment can be made. Current knowledge, reviewed in this article, suggests that no acute complications secondary to retroviral-mediated gene transfer are likely, but the possibility of long-term or unforeseen sequelae in patients suggests the need for post-treatment monitoring.

Developmental regulation of lck gene expression in T lymphocytes

In the mouse and human, mRNA transcripts encoding the lymphocyte-specific protein tyrosine kinase p56lck are derived from two separate promoters resulting in heterogeneity in the 5' untranslated region sequence. The proximal promoter lies just 5' to the coding region for the gene and is active only in thymocytes. In contrast, the distal promoter lies 34 kilobases (kb) 5' in the human, and is active both in thymocytes and mature peripheral T cells. As previously reported, transgenic mice bearing functional proximal promoter sequence juxtaposed with the SV40 large T antigen gene invariably develop lymphoid tumors confined to the thymus. In the current work, transgenic mice bearing a 2.6-kb fragment of the human distal promoter fused to the SV40 large T antigen gene express large T antigen in thymocytes and in peripheral lymphoid cells, and develop tumors of both the thymus and the peripheral lymphoid organs. The ability of the human distal promoter to function appropriately in transgenic mice is consistent with the strong similarity observed between the mouse and human distal promoter sequences. With the exception of a single short interval that serves as a target for binding of nuclear factors, significant sequence similarity is not seen when the distal and proximal promoter sequences are compared. Hence, developmentally regulated, lineage-specific transcription of the lck gene is mediated by distinct promoter sequences that appear to be capable of functioning independently.

Changes in the relative abundance of type I and type II lck mRNA transcripts suggest differential promoter usage during T-cell development

The lck gene, which encodes the lymphoid cell-specific tyrosine protein kinase p56lck, is expressed from two widely separated promoters. The proximal promoter gives rise to a type I lck transcript, and the distal promoter gives rise to a type II transcript. We found that the ratio of the two transcripts changed during T-cell maturation. Type I lck mRNA was twofold more abundant than the type II transcript in early fetal thymocytes. In the adult, the type I and type II lck mRNAs were present in approximately equal amounts in immature thymocytes expressing the heat-stable antigen. In contrast, there was five- to ninefold more type II lck than type I lck mRNA in more mature thymocytes that did not express the heat-stable antigen and in splenic T cells. This change in relative transcript abundance probably reflects activation of the distal promoter and inactivation of the proximal promoter during T-cell maturation in the thymus. It is possible that the two promoters are regulated by different trans-acting factors whose expression is regulated during T-cell maturation.

Changes in the relative abundance of type I and type II lck mRNA transcripts suggest differential promoter usage during T-cell development

The lck gene, which encodes the lymphoid cell-specific tyrosine protein kinase p56lck, is expressed from two widely separated promoters. The proximal promoter gives rise to a type I lck transcript, and the distal promoter gives rise to a type II transcript. We found that the ratio of the two transcripts changed during T-cell maturation. Type I lck mRNA was twofold more abundant than the type II transcript in early fetal thymocytes. In the adult, the type I and type II lck mRNAs were present in approximately equal amounts in immature thymocytes expressing the heat-stable antigen. In contrast, there was five- to ninefold more type II lck than type I lck mRNA in more mature thymocytes that did not express the heat-stable antigen and in splenic T cells. This change in relative transcript abundance probably reflects activation of the distal promoter and inactivation of the proximal promoter during T-cell maturation in the thymus. It is possible that the two promoters are regulated by different trans-acting factors whose expression is regulated during T-cell maturation.

lck suppresses gene expression from various promoters including human T-cell leukemia virus type I promoter

The T-lymphocyte-specific tyrosine kinase gene, lck, is expressed in T-lymphocyte cell lines, except for several human T-cell leukemia virus type I(HTLV-I)-transformed T-lymphocyte cell lines, which produce HTLV-I. By introducing an lck-expression vector, we found that lck product suppresses gene expression from HTLV-I promoter in a transient assay. Moreover, various other promoters of cellular genes or viruses were found to have their transcriptional activity repressed by lck.

Structure of the human lck gene: differences in genomic organisation within src-related genes affect only N-terminal exons

Although cDNA sequences coding for several Rous sarcoma virus Src-related protein tyrosine kinases (PTKs) have been reported for several years, knowledge of the structure and organisation of genes of the src family is still limited. In this work, a detailed structure and organisation of the human lck gene is reported. A 17-kb genomic clone encoding human p56 Lck, a lymphocyte-specific PTK of the Src-related subfamily, has been isolated. The human lck gene is organized in 13 exons, one more than in the human cellular (c)-src gene. The twelve coding exons are located in this clone, whereas the putative 5'-noncoding exon is probably located very far upstream from the second exon. Splicing sites for exons 4 to 12, which encode both conserved phospholipase-C-like and catalytic domains of the Src-like PTKs, arise exactly at the same position for the human lck, human c-src and c-fgr genes. The only differences concern the splice sites of exons 1' and 2, which encode the unique N-terminal domain of human Lck. These results give further evidence that the different PTKs of the Src-like family have probably evolved through the mechanism of exon shuffling.

Selective expression of alternative lck mRNAs in human malignant cell lines

The lck protein tyrosine kinase is normally expressed in a cell type-specific fashion, with mRNA being confined to cells of lymphoid lineage. Despite this highly specific pattern of expression in normal tissues, lck mRNA has also been detected in selected cell lines derived from human nonlymphoid neoplasms. In this study we explored the mechanisms underlying the expression of lck mRNA within human nonlymphoid neoplastic cell lines. We determined that lck mRNA expression was correlated with transcriptional activation and that there was no evidence for genomic rearrangement or amplification within the lck coding region to account for the expression of lck mRNA in the nonlymphoid neoplastic cell lines. The lck gene has previously been shown to contain two distinct promoter elements. In this study, we demonstrated that lck-producing cell lines derived from human nonlymphoid neoplasms expressed transcripts initiated exclusively from the 3'-most promoter element (3' promoter). In contrast, lymphoid cell lines derived from nonmalignant sources expressed lck transcripts exclusively initiated from the 5'-most promoter element (5' promoter). Most cell lines derived from human lymphoid neoplasms express lck transcripts initiated from both the 5' and 3' promoters in various ratios. Thus, lck expression in a variety of malignant cell lines results from a selective induction of transcription from the 3' promoter.

Structure of the two promoters of the human lck gene: differential accumulation of two classes of lck transcripts in T cells

The human T-cell- or lymphocyte-specific gene, lck, encodes a tyrosine kinase and is a member of the src family. In this report we demonstrate that there are two classes of human lck transcripts (types I and II), containing different 5'-untranslated regions, which are expressed from two distinct promoters. No apparent sequence similarity was observed between the 5'-flanking regions of the two promoters. The expression of lck in human T-cell leukemia and carcinoma cell lines and in human peripheral blood T lymphocytes was examined by S1 nuclease and primer extension mapping and by Northern (RNA) blot analysis of total cellular RNA. The following results were obtained. (i) Two RNA start sites in the downstream promoter were used to generate type I transcripts. (ii) The major human type I start site has not been described for the mouse. (iii) At least five RNA start sites in the upstream promoter were used to generate type II transcripts. (iv) In T cells and in two colon carcinoma cell lines, type II transcripts were present in higher amounts than type I transcripts. (v) In T cells treated with phytohemagglutinin, tetradecanoylphorbol acetate, and cyclosporin A, the modulation of lck expression was associated primarily with changes in levels of type II transcripts. The above results suggest that the two human lck promoters are utilized differentially and may be regulated independently during certain physiological states.

Selective expression of alternative lck mRNAs in human malignant cell lines

The lck protein tyrosine kinase is normally expressed in a cell type-specific fashion, with mRNA being confined to cells of lymphoid lineage. Despite this highly specific pattern of expression in normal tissues, lck mRNA has also been detected in selected cell lines derived from human nonlymphoid neoplasms. In this study we explored the mechanisms underlying the expression of lck mRNA within human nonlymphoid neoplastic cell lines. We determined that lck mRNA expression was correlated with transcriptional activation and that there was no evidence for genomic rearrangement or amplification within the lck coding region to account for the expression of lck mRNA in the nonlymphoid neoplastic cell lines. The lck gene has previously been shown to contain two distinct promoter elements. In this study, we demonstrated that lck-producing cell lines derived from human nonlymphoid neoplasms expressed transcripts initiated exclusively from the 3'-most promoter element (3' promoter). In contrast, lymphoid cell lines derived from nonmalignant sources expressed lck transcripts exclusively initiated from the 5'-most promoter element (5' promoter). Most cell lines derived from human lymphoid neoplasms express lck transcripts initiated from both the 5' and 3' promoters in various ratios. Thus, lck expression in a variety of malignant cell lines results from a selective induction of transcription from the 3' promoter.

Structure of the two promoters of the human lck gene: differential accumulation of two classes of lck transcripts in T cells

The human T-cell- or lymphocyte-specific gene, lck, encodes a tyrosine kinase and is a member of the src family. In this report we demonstrate that there are two classes of human lck transcripts (types I and II), containing different 5'-untranslated regions, which are expressed from two distinct promoters. No apparent sequence similarity was observed between the 5'-flanking regions of the two promoters. The expression of lck in human T-cell leukemia and carcinoma cell lines and in human peripheral blood T lymphocytes was examined by S1 nuclease and primer extension mapping and by Northern (RNA) blot analysis of total cellular RNA. The following results were obtained. (i) Two RNA start sites in the downstream promoter were used to generate type I transcripts. (ii) The major human type I start site has not been described for the mouse. (iii) At least five RNA start sites in the upstream promoter were used to generate type II transcripts. (iv) In T cells and in two colon carcinoma cell lines, type II transcripts were present in higher amounts than type I transcripts. (v) In T cells treated with phytohemagglutinin, tetradecanoylphorbol acetate, and cyclosporin A, the modulation of lck expression was associated primarily with changes in levels of type II transcripts. The above results suggest that the two human lck promoters are utilized differentially and may be regulated independently during certain physiological states.