An EZH2 polymorphism is associated with clinical outcome in metastatic colorectal cancer patients.

BACKGROUND: Despite therapeutic innovations, metastatic colorectal cancer (mCRC) is still characterized by poor prognosis and few molecular markers predict the risk of progression. Polycomb group genes (PcGs) are epigenetic modifiers involved in tumor suppressor gene silencing. PcG member EZH2 mediates gene silencing through histone-H3 lysine-27 methylation. In colorectal cancer (CRC), EZH2 overexpression predicts shorter survival. Recently, four EZH2 single-nucleotide polymorphisms (SNPs) have been described. The present study was aimed at evaluating the correlation between EZH2 SNPs and outcome parameters in mCRC patients. PATIENTS AND METHODS: DNA was extracted from blood samples of 110 mCRC patients treated with first-line 5-fluorouracil, folinic acid, irinotecan (FOLFIRI) and bevacizumab. Genotyping was carried out by real-time PCR. Genotype was used to predict objective response, progression-free survival (PFS) and overall survival (OS). EZH2 messenger RNA levels were evaluated on lymphocytes of a parallel cohort of 50 CRC patients. RESULTS: One allelic variant (rs3757441 C/C versus C/T or T/T) was significantly associated with shorter PFS and OS (P < 0.01 and P < 0.05, respectively). At multivariate analysis, the same variant resulted an independent predictor of PFS and OS (P < 0.05). The C/C variant was associated with significantly higher EZH2 expression (P < 0.05). CONCLUSION: An EZH2 SNP may be useful to predict clinical outcome in mCRC patients.

Specific inhibition of lymphokine biosynthesis and autocrine growth using antisense oligonucleotides in Th1 and Th2 helper T cell clones.

T helper cells have recently been divided into two subsets. The Th1 subset secretes and responds to IL-2 in an autocrine manner. The Th2 subset upon mitogen or antigen stimulation releases IL-4. Here we describe a novel technology that allowed us to confirm this distinction. We have used synthetic oligonucleotides complementary to the 5' end of mouse IL-2 and IL-4 to specifically block the biosynthesis of IL-2 or IL-4 in two murine helper T cell clones from the Th1 or Th2 subset. We show that the antisense IL-2 oligonucleotide inhibited the proliferation of the Th1 clone and had no effect on the Th2 clone. In parallel experiments, the antisense IL-4 oligonucleotide blocked the proliferation of the Th2 clone and not the proliferation of the Th1 clone. The inhibition was significantly reversed in both cases by the addition of the relevant lymphokine (IL-2 in the case of the Th1 clone, IL-4 in the case of the Th2 clone). Northern analysis, using cDNA probes specific for the two lymphokines, showed a decrease in the steady-state level of the relevant lymphokine mRNA, suggesting the specific degradation of the mRNA by an RNase H-like enzymatic activity. This strategy, which allows the specific blockade of the biosynthesis of a lymphokine, could be useful for future studies on the role of each T helper subset in physiological immune responses.

Epigenetic gene regulation in stem cells and correlation to cancer.

Through the classic study of genetics, much has been learned about the regulation and progression of human disease. Specifically, cancer has been defined as a disease driven by genetic alterations, including mutations in tumor-suppressor genes and oncogenes, as well as chromosomal abnormalities. However, the study of normal human development has identified that in addition to classical genetics, regulation of gene expression is also modified by 'epigenetic' alterations including chromatin remodeling and histone variants, DNA methylation, the regulation of polycomb group proteins, and the epigenetic function of non-coding RNA. These changes are modifications inherited during both meiosis and mitosis, yet they do not result in alterations of the actual DNA sequence. A number of biological questions are directly influenced by epigenetics, such as how does a cell know when to divide, differentiate or remain quiescent, and more importantly, what happens when these pathways become altered? Do these alterations lead to the development and/or progression of cancer? This review will focus on summarizing the limited current literature involving epigenetic alterations in the context of human cancer stems cells (CSCs). The extent to which epigenetic changes define cell fate, identity, and phenotype are still under intense investigation, and many questions remain largely unanswered. Before discussing epigenetic gene silencing in CSCs, the different classifications of stem cells and their properties will be introduced. This will be followed by an introduction to the different epigenetic mechanisms. Finally, there will be a discussion of the current knowledge of epigenetic modifications in stem cells, specifically what is known from rodent systems and established cancer cell lines, and how they are leading us to understand human stem cells.

Regulation of expression of the interleukin-2 receptor on hematopoietic cells by interleukin-3.

Remarkable similarities in the intracellular and genetic events occur when lymphoid and hematopoietic cells are exposed to their specific growth factors. The interleukin-2 (IL-2) receptor, whose cell-surface expression is an absolute requirement for the growth and differentiation of lymphoid cells, was detected on various nonlymphoid hematopoietic cell types in this study. Cell lines consisting either of granulocyte-macrophage precursors or mast cells, which are dependent on interleukin-3 (IL-3) for their growth, expressed high levels of the IL-2 receptor on their surface. Analysis of the binding characteristics of these receptors with 125I-labeled recombinant IL-2 revealed that only receptors with low affinity for IL-2 were present on these cells. Addition of purified recombinant IL-3 to these cell lines led to an increase in IL-2 receptor gene expression within 1 hour in isolated nuclei. This IL-3--induced increase in the number of IL-2 receptors on the cell surface is maximal within 24 hours. Addition of 10,000 units of IL-2 to these cells had no apparent effect on their growth or differentiation. The presence of the receptor with only low affinity for IL-2 on hematopoietic cells and the regulation by IL-3 suggest that this receptor is involved in some important metabolic event in hematopoiesis.

Stress and immune responses after surgical treatment for regional breast cancer.

BACKGROUND: Adults who undergo chronic stress, such as the diagnosis and surgical treatment of breast cancer, often experience adjustment difficulties and important biologic effects. This stress can affect the immune system, possibly reducing the ability of individuals with cancer to resist disease progression and metastatic spread. We examined whether stress influences cellular immune responses in patients following breast cancer diagnosis and surgery. METHODS: We studied 116 patients recently treated surgically for invasive breast cancer. Before beginning their adjuvant therapy, all subjects completed a validated questionnaire assessing the stress of being cancer patients. A 60-mL blood sample taken from each patient was subjected to a panel of natural killer (NK) cell and T-lymphocyte assays. We then developed multiple regression models to test the contribution of psychologic stress in predicting immune function. All regression equations controlled for variables that might exert short- or long-term effects on these responses, and we also ruled out other potentially confounding variables. RESULTS: We found, reproducibly between and within assays, the following: 1) Stress level significantly predicted lower NK cell lysis, 2) stress level significantly predicted diminished response of NK cells to recombinant interferon gamma, and 3) stress level significantly predicted decreased proliferative response of peripheral blood lymphocytes to plant lectins and to a monoclonal antibody directed against the T-cell receptor. CONCLUSIONS: The data show that the physiologic effects of stress inhibit cellular immune responses that are relevant to cancer prognosis, including NK cell toxicity and T-cell responses. Additional, longitudinal studies are needed to determine the duration of these effects, their health consequences, and their biologic and/or behavioral mechanisms.

Five versus more than five years of tamoxifen therapy for breast cancer patients with negative lymph nodes and estrogen receptor-positive tumors.

BACKGROUND: In 1982, the National Surgical Adjuvant Breast and Bowel Project initiated a randomized, double-blinded, placebo-controlled trial (B-14) to determine the effectiveness of adjuvant tamoxifen therapy in patients with primary operable breast cancer who had estrogen receptor-positive tumors and no axillary lymph node involvement. The findings indicated that tamoxifen therapy provided substantial benefit to patients with early stage disease. However, questions arose about how long the observed benefit would persist, about the duration of therapy necessary to maintain maximum benefit, and about the nature and severity of adverse effects from prolonged treatment. PURPOSE: We evaluated the outcome of patients in the B-14 trial through 10 years of follow-up. In addition, the effects of 5 years versus more than 5 years of tamoxifen therapy were compared. METHODS: In the trial, patients were initially assigned to receive either tamoxifen at 20 mg/day (n = 1404) or placebo (n = 1414). Tamoxifen-treated patients who remained disease free after 5 years of therapy were then reassigned to receive either another 5 years of tamoxifen (n = 322) or 5 years of placebo (n = 321). After the study began, another group of patients who met the same protocol eligibility requirements as the randomly assigned patients were registered to receive tamoxifen (n = 1211). Registered patients who were disease free after 5 years of treatment were also randomly assigned to another 5 years of tamoxifen (n = 261) or to 5 years of placebo (n = 249). To compare 5 years with more than 5 years of tamoxifen therapy, data relating to all patients reassigned to an additional 5 years of the drug were combined. Patients who were not reassigned to either tamoxifen or placebo continued to be followed in the study. Survival, disease-free survival, and distant disease-free survival (relating to failure at distant sites) were estimated by use of the Kaplan-Meier method; differences between the treatment groups were assessed by use of the logrank test. The relative risks of failure (with 95% confidence intervals [CIs]) were determined by use of the Cox proportional hazards model. Reported P values are two-sided. RESULTS: Through 10 years of follow-up, a significant advantage in disease-free survival (69% versus 57%, P < .0001; relative risk = 0.66; 95% CI = 0.58-0.74), distant disease-free survival (76% versus 67%, P < .0001; relative risk = 0.70; 95% CI = 0.61-0.81), and survival (80% versus 76%, P = .02; relative risk = 0.84; 95% CI = 0.71-0.99) was found for patients in the group first assigned to receive tamoxifen. The survival benefit extended to those 49 years of age or younger and to those 50 years of age or older. Tamoxifen therapy was associated with a 37% reduction in the incidence of contralateral (opposite) breast cancer (P = .007). Through 4 years after the reassignment of tamoxifen-treated patients to either continued-therapy or placebo groups, advantages in disease-free survival (92% versus 86%, P = .003) and distant disease-free survival (96% versus 90%, P = .01) were found for those who discontinued tamoxifen treatment. Survival was 96% for those who discontinued tamoxifen compared with 94% for those who continued tamoxifen treatment (P = .08). A higher incidence of thromboembolic events was seen in tamoxifen-treated patients (through 5 years, 1.7% versus 0.4%). Except for endometrial cancer, the incidence of second cancers was not increased with tamoxifen therapy. CONCLUSIONS AND IMPLICATIONS: The benefit from 5 years of tamoxifen therapy persists through 10 years of follow-up. No additional advantage is obtained from continuing tamoxifen therapy for more than 5 years.

Interleukin 6 activates androgen receptor-mediated gene expression through a signal transducer and activator of transcription 3-dependent pathway in LNCaP prostate cancer cells.

Interleukin 6 (IL-6) is a cytokine that regulates not only immune and inflammatory responses but also the growth of some tumors, including prostate carcinomas. IL-6 signals through Janus kinase, signal transducer and activator of transcription 3 (STAT3), and mitogen-activated protein kinase and is also able to induce androgen receptor (AR)-mediated gene activation in prostate cancer, which is an important process in prostate cancer androgen-independent progression. We now show that IL-6-induced AR-mediated gene activation requires the activation of STAT3 by IL-6 in LNCaP prostate cancer cells. In particular, STAT3 associates with AR in an androgen-independent but IL-6-dependent manner. Inhibition of STAT3 rather than mitogen-activated protein kinase results in inhibition of AR-mediated gene activation in response to IL-6. These findings not only identify STAT3 as an important signaling molecule required for IL-6-signaling to induce AR-mediated gene activation in prostate carcinoma cells but also reveal the importance of activated STAT3 in human tumor development and progression.

Characterization of a class 3 tyrosine kinase.

In an effort to identify unique tyrosine kinases found in human leukemia cell lines, we utilized polymerase chain reaction (PCR) technology and degenerate oligonucleotide primers to produce a cDNA library of kinase catalytic domains found in the human monocytic cell line AML-193. This search yielded a member of the class 3 tyrosine kinases closely related to the murine kinase FD-22. Previous work has identified this kinase as JAK1. This class of tyrosine kinases is characterized by being ubiquitously expressed, lacking both a ligand-binding domain and a SH2 domain, while containing a second domain similar to a degenerate kinase domain. Our studies focused on the further characterization of this class 3 tyrosine kinase using Northern blot analysis to demonstrate an increase in steady-state mRNA by interferon-gamma in human monocytes. A human-hamster somatic cell hybrid panel and linkage mapping was used to assign JAK1 (aml-116) to human chromosome 1.

Adjuvant CMFVP versus adjuvant CMFVP plus ovariectomy for premenopausal, node-positive, and estrogen receptor-positive breast cancer patients: a Southwest Oncology Group study.

PURPOSE: To determine whether the addition of surgical ovariectomy to standard chemotherapy prolongs disease-free survival (DFS) and overall survival in premenopausal patients with estrogen receptor (ER)-positive operable breast cancer with positive axillary nodes. PATIENTS AND METHODS: Three hundred fourteen premenopausal patients with ER-positive, node-positive breast cancer were enrolled between July 1979 and July 1989. Patients were stratified according to number of involved nodes and type of primary surgery and randomized to receive either of the following: (1) cyclophosphamide 60 mg/m2/d by mouth for 1 year, methotrexate 15 mg/m2 intravenously (i.v.) weekly for 1 year, fluorouracil (5-FU) 400 mg/m2 i.v. weekly for 1 year, vincristine .625 mg/m2 i.v. weekly for the first 10 weeks, and prednisone weeks 1 to 10 with doses decreasing from 30 mg/m2 to 2.5 mg/m2 (CMFVP); or (2) bilateral ovariectomy followed by CMFVP. RESULTS: The median follow-up time is 7.7 years and the maximum 13.2 years. Treatment arms are not significantly different with respect to either survival or DFS (one-sided log-rank, P = .55 and .70, respectively). The 7-year survival rate is 71% on the CMFVP arm and 73% on CMFVP plus ovariectomy. No significant differences were observed in node or receptor level subsets. CONCLUSION: We conclude that, in this study, the addition of ovariectomy did not improve results over chemotherapy alone in the treatment of premenopausal women with node-positive, ER-positive, operable breast cancer. Our sample size was too small to detect a small improvement. The death hazards ratio of CMFVP/CMFVP plus ovariectomy was 1.22 (95% confidence interval [CI], .79 to 1.89).

Adjuvant CMFVP versus tamoxifen versus concurrent CMFVP and tamoxifen for postmenopausal, node-positive, and estrogen receptor-positive breast cancer patients: a Southwest Oncology Group study.

PURPOSE: To compare chemohormonal therapy, chemotherapy alone, and hormonal therapy alone in postmenopausal patients with estrogen receptor (ER)-positive operable breast cancer and positive axillary nodes with respect to survival and disease-free survival (DFS). PATIENTS AND METHODS: Eight hundred ninety-two postmenopausal women with ER-positive, node-positive breast cancer were enrolled by the Southwest Oncology Group (SWOG) from July 1979 to March 1989 and 74 by the Eastern Cooperative Oncology Group (ECOG) between June 1987 and March 1989. Patients were stratified according to number of involved nodes and type of primary surgery and randomized to receive the following: (1) tamoxifen 10 mg twice daily by mouth for 1 year; (2) cyclophosphamide 60 mg/m2/d by mouth for 1 year, methotrexate 15 mg/m2 intravenously (IV) weekly for 1 year, fluorouracil (5-FU) 400 mg/m2 IV weekly for 1 year, vincristine .625 mg/m2 IV weekly for the first 10 weeks, and prednisone during weeks 1 to 10 with doses decreasing from 30 mg/m2 to 2.5 mg/m2 (CMFVP); or (3) the combination of tamoxifen and CMFVP. RESULTS: The median follow-up duration is 6.5 years, with a maximum of 12.8 years. Treatment arms are not significantly different with respect to either survival or DFS (log-rank, 2 df, P = .82 and .23, respectively). The 5-year survival rate is 77% for the tamoxifen arm, 78% for CMFVP, and 75% for the combination. No significant differences were observed in node or receptor level subsets. Severe or worse toxicity was experienced by 56% of patients on CMFVP and 61% on CMFVP plus tamoxifen, compared with 5% on tamoxifen alone. CONCLUSION: CMFVP chemotherapy, either alone or in combination with tamoxifen, has not been shown to be superior to tamoxifen alone in the treatment of postmenopausal women with node-positive, ER-positive, operable breast cancer.

Tamoxifen and chemotherapy for axillary node-negative, estrogen receptor-negative breast cancer: findings from National Surgical Adjuvant Breast and Bowel Project B-23.

PURPOSE: Uncertainty about the relative worth of doxorubicin/cyclophosphamide (AC) and cyclophosphamide/methotrexate/fluorouracil (CMF), as well as doubt about the propriety of giving tamoxifen (TAM) with chemotherapy to patients with estrogen receptor-negative tumors and negative axillary nodes, prompted the National Surgical Adjuvant Breast and Bowel Project to initiate the B-23 study. PATIENTS AND METHODS: Patients (n = 2,008) were randomly assigned to CMF plus placebo, CMF plus TAM, AC plus placebo, or AC plus TAM. Six cycles of CMF were given for 6 months; four cycles of AC were administered for 63 days. TAM was given daily for 5 years. Relapse-free survival (RFS), event-free survival (EFS), and survival (S) were determined by using life-table estimates. Tests for heterogeneity of outcome used log-rank statistics and Cox proportional hazards models to detect differences across all groups and according to chemotherapy and hormonal therapy status. RESULTS: No significant difference in RFS, EFS, or S was observed among the four groups through 5 years (P =.96,.8, and.8, respectively), for those aged < or = 49 years (P =.97,.5, and.9, respectively), or for those aged > or = 50 years (P =.7,.6, and.6, respectively). A comparison between all CMF- and all AC-treated patients demonstrated no significant differences in RFS (87% at 5 years in both groups, P =.9), EFS (83% and 82%, P =.6), or S (89% and 90%, P =.4). There were no significant differences in RFS, EFS, or S between CMF and AC in patients aged < or = 49 or > or = 50 years. No significant difference in any outcome was observed when chemotherapy-treated patients who received placebo were compared with those given TAM. RFS in both groups was 87% (P =.6), 87% in patients aged < or = 49 (P =.9), and 88% and 87%, respectively (P =.4), in those aged > or = 50 years. CONCLUSION: There was no significant difference in the outcome of patients who received AC or CMF. TAM with either regimen resulted in no significant advantage over that achieved from chemotherapy alone.

Characterization of CD4 glycoprotein determinant-HIV envelope protein interactions: perspectives for analog and vaccine development.

The CD4 surface determinant, previously associated as a phenotypic marker for helper/inducer subsets of T lymphocytes, has now been critically identified as the binding/entry protein for human immunodeficiency viruses (HIV). The human CD4 molecule is readily detectable on monocytes, T lymphocytes, and brain tissues. Soluble HIV (HTLV IIIB) envelope protein (gp120) binds native or recombinant CD4 with equal affinity estimated to be 4 to 8 nM kDa. All human tissue sources of CD4 bind radiolabeled gp120 to the same relative degree; however, the murine homologous protein, L3T4, does not bind the HIV envelope protein. Lack of sufficient recognition by the recombinant L3T4 molecule suggests divergence in the gp120-binding epitope. The binding of gp120 to CD4 is dependent upon intact sulfhydryl bonds within cysteine residues and glycosylation. Deglycosylated native gp120 is unable to bind CD4 under physiological conditions. Recombinant deglycosylated fragments cannot bind to the CD4 receptor, although they serve as immunogen for neutralizing antibody development. A number of synthetic peptides to putative critical domains of gp120 have been studied for their antagonism of native gp120 binding. Peptide T analogs or synthetic cogeners of Neuroleukin proposed to bind the CD4 determinant involved in gp120 binding had no competitive displacement of native gp120 binding as assessed by two independent methods that measure gp120 interaction with CD4. Recombinant C-terminal fragments, also containing other putative domains, did not displace native gp120 from CD4. Glycosylation appears to be critical in the maintenance of the structure of the binding domain of gp120. Native gp120 binding to CD4 is sufficient for the activation of cellular metabolism that alters target cell gene expression and differentiation, suggesting that the virus binding contributes to the activation of the host cell.

Tyrphostin AG-490 inhibits cytokine-mediated JAK3/STAT5a/b signal transduction and cellular proliferation of antigen-activated human T cells.

Janus kinase 3 (JAK3) is a cytoplasmic tyrosine kinase required for T cell development and activated by cytokines that utilize the interleukin-2 (IL-2) receptor common gamma chain (gamma(c)). Genetic inactivation of JAK3 is manifested as severe combined immunodeficiency disease (SCID) in humans and mice. These findings have suggested that JAK3 represents a pharmacological target to control certain lymphoid-derived diseases. Here we provide novel evidence that AG-490 potently inhibits the autokinase activity of JAK3 and tyrosine phosphorylation and DNA binding of signal transducer and activator of transcription 5a and 5b (STAT5a/b). Similar inhibitory effects were observed with other cytokines that use gamma(c). AG-490 also inhibited IL-2-mediated proliferative growth in human T cells with an IC50) = 25 microM that was partially recoverable. Moreover, we demonstrate that this inhibitor prevented tetanus toxoid antigen-specific T cell proliferation and expansion but failed to block activation of Zap70 or p56Lck after anti-CD3 stimulation of human T cells. Taken together, these findings suggest that AG-490 inhibits the JAK3-mediated Type II signaling pathway but not the T cell receptor-derived Type I pathway and possesses therapeutic potential for T cell-derived pathologies such as graft-versus-host disease, allergy, and autoimmune disorders.

Sensitivity of the amylase-creatinine clearance ratio in acute pancreatitis.

An elevated amylase-creatinine clearance ratio has been established as being highly specific for the diagnosis of acute pancreatitis. In the present study, the sensitivity of this test was compared to that of the serum amylase and the one-hour urinary amylase test in 29 patients with acute pancreatitis. Abnormal elevations of the amylase-creatinine clearance ratio were found less frequently than abnormal elevations of the serum and one-hour urinary amylases. Moreover, abnormal elevations of the amylase-creatinine clearance ratio showed less deviation from normal and values returned to normal sooner than those of the serum and one-hour urinary amylases. When compared to the serum amylase and the one-hour urinary amylase tests, the amylase-creatinine clearance ratio is a relatively insensitive test in patients with acute pancreatitis.

Purification and properties of the pyruvate kinase isozyme M1 from the pig brain.

There are four pyruvate kinase isozymes in vertebrate tissues, designated as L, M1, M2, and R. Although pyruvate kinases have been purified and characterized from pig liver, muscle, kidney, and heart, the brain isozyme has not. The aim of this work was to purify, characterize and make an isozymic designation for the pig brain pyruvate kinase. Purification was accomplished by chromatography on phosphocellulose, Sephadex G200, and blue-dextran agarose columns. The molecular weight of the native enzyme was determined by sucrose density centrifugation. The degree of purity, and subunit molecular weight were determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The isoelectric point was estimated by the rapid isoelectric focusing method in sucrose gradients. The pH optimum, and kinetics in the presence and absence of fructose-1,6-diphosphate were determined spectrophotometrically. The purification scheme used resulted in a 382-fold purification of pig brain pyruvate kinase, and a final specific activity of 191 Units/mg protein. As estimated by scanning of the sodium dodecyl sulfate polyacrylamide gels, the purification scheme also resulted in a preparation that was of at least 98% purity. Pig brain pyruvate kinase has a native molecular weight of approx. 230,000, and a subunit molecular weight of approx. 60,000. The pI was determined to be approximately 8.0, while the pH optimum was estimated at pH 7.4. Fructose-1,6-diphosphate had no effect on either the Km for phospho(enol)pyruvate, or the Vmax of the reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin activates Ras via signaling proteins SHC, growth factor receptor bound 2, and son of sevenless.

Identification of the signal transduction pathways used by PRL is essential for understanding the role of PRL receptors in growth and differentiation processes. Early cellular mediators of PRL receptor activation include tyrosine kinases of the Janus kinase (JAK) and SRC families, with rapid nuclear signaling via tyrosine phosphorylated signal transducers and activators of transcription. In the present study we provide the first demonstration of PRL-induced activation of Ras, an oncogenic protein that supports an alternative signaling route from the membrane to the nucleus. PRL stimulated Ras in rat Nb2-SP lymphoma cells, as detected by a 2.0-fold increase in the GTP-bound state of the molecule (P < 0.01). This activation was associated with marked tyrosine phosphorylation and increased membrane association of the 52-kilodalton form of SHC. Moreover, PRL induced binding of SHC to growth factor receptor bound 2 and the guanine-nucleotide exchange factor son of sevenless, a common method used by growth factor receptors to activate Ras. In contrast, no apparent regulation by PRL of Ras via VAV or p120 Ras-guanosine triphosphatase-activating protein was detected, based upon an absence of PRL-inducible tyrosine phosphorylation of these proteins. Collectively, these results provide a molecular bridge between activation of PRL receptor-associated tyrosine kinases and subsequent stimulation of the serine/threonine kinase Raf-1, an established Ras target that was recently shown to be activated by PRL in Nb2 cells. We conclude that PRL is able to activate Ras via recruitment of the signaling proteins SHC, growth factor receptor bound 2, and son of sevenless in Nb2 cells. Moreover, PRL induced tyrosine phosphorylation of SHC in two of three PRL-responsive human breast cancer cell lines, suggesting that SHC-mediated Ras activation is a commonly used signaling strategy by PRL.

JAK2 activation and cell proliferation induced by antibody-mediated prolactin receptor dimerization.

Cytokines that interact with receptors of the hematopoietin super-family have recently been reported to stimulate receptor-associated JAK tyrosine kinases, including PRL activation of JAK2. Unlike other tyrosine kinases, none of the JAK kinases has thus far been implicated in oncogenesis, and their involvement in growth signaling has not been established. Using the PRL-dependent pre-T-cell line Nb2, the present study provided a link between bivalent dimerization of a hematopoietin receptor and activation of its associated JAK kinase, and demonstrated a strong positive correlation between the mitogenic potency of a series of bivalent anti-PRL receptor antibodies and the degree of induced tyrosine phosphorylation of JAK2. Antibody bivalency was required for JAK2 phosphorylation. Monovalent anti-PRL receptor Fab fragments alone were inactive, but their activity could be partially restored by cross-linking with bivalent anti-Fab antibodies. Additional evidence for antibody-induced receptor dimerization was provided by a bell-shaped dose-response curve for the most potent receptor agonist, monoclonal antibody T6. This phenomenon is typically seen at pharmacological concentrations of bivalent ligands, when bound ligand molecules fail to adjoin a second receptor due to occupancy. The present study provided functional support for a model of PRL receptor triggering by ligand-induced receptor homodimerization and subsequent activation of the associated tyrosine kinase JAK2.

Cloning of the gene encoding rat JAK2, a protein tyrosine kinase.

A complete cDNA clone encoding the rat JAK2 protein tyrosine kinase was isolated from an Nb2-SP (rat pre-T lymphoma cell line) cDNA library. The nucleotide (nt) and deduced amino acid (aa) sequences for this clone were determined and an open reading frame of 3399 bp, encoding a protein of a deduced mass of 130 kDa, was found. The coding regions of the rat and murine Jak2 clones share 93.4% nt identity and 97.1% aa identity. Northern analysis demonstrated that the 5-kb mRNA is highly abundant in brain and spleen, less abundant in skeletal muscle and testis, and detectable in kidney, heart, lung and liver. Translation of the rat Jak2 mRNA in rabbit reticulocytes results in a protein which is specifically immunoprecipitated by antibodies (Ab) recognizing JAK2, but not by Ab recognizing JAK1.

Molecular cloning of FKHRL1P2, a member of the developmentally regulated fork head domain transcription factor family.

Here we report the expression of a fork head domain protein in human T helper cells. We cloned and characterized a fork head cDNA from human T helper cell mRNA using differential display RT-PCR. The cDNA contains a 546-nucleotide (nt) open reading frame (ORF) that codes for the carboxyl-terminal 180 amino acids (aa) of the recently identified fkhrl1 gene. This ORF does not contain the characteristic DNA-binding domain found in members of the forkhead protein family. In-vitro transcription/translation of this cDNA expressed a protein of approximately 20 kDa. We have generated antibodies that specifically immunoprecipitated the in-vitro-translated 20-kDa protein. This antibody also recognizes in human T lymphocytes a 70-kDa protein corresponding in size to that predicted for the fkhrl1 gene product. The mRNA levels for fkhrl1 is elevated in T helper-induced lymphocytes in comparison to PHA-stimulated T lymphocytes. Further characterization of FKHRL1 and its related family members should shed light on the transcriptional mechanisms of this fork head gene subfamily and their role in T helper cell differentiation and regulation of cell growth.