Interleukin-7 regulates c-myc expression in murine T cells and thymocytes: a role for tyrosine kinase(s) and calcium mobilization

Targeting Molecular Signaling Pathways and Cytokine Responses to Modulate c-MYC in Acute Myeloid Leukemia

Overexpression of the MYC oncogene, encoding c-MYC protein, contributes to the pathogenesis and drug resistance of acute myeloid leukemia (AML) and many other hematopoietic malignancies. Although standard chemotherapy has predominated in AML therapy over the past five decades, the clinical outcomes and patient response to treatment remain suboptimal. Deeper insight into the molecular basis of this disease should facilitate the development of novel therapeutics targeting specific molecules and pathways that are dysregulated in AML, including fms-like tyrosine kinase 3 (FLT3) gene mutation and cluster of differentiation 33 (CD33) protein expression. Elevated expression of c-MYC is one of the molecular features of AML that determines the clinical prognosis in patients. Increased expression of c-MYC is also one of the cytogenetic characteristics of drug resistance in AML. However, direct targeting of c-MYC has been challenging due to its lack of binding sites for small molecules. In this review, we focused on the mechanisms involving the bromodomain and extra-terminal (BET) and cyclin-dependent kinase 9 (CDK9) proteins, phosphoinositide-Akt-mammalian target of rapamycin (PI3K/AKT/mTOR) and Janus kinase-signal transduction and activation of transcription (JAK/STAT) pathways, as well as various inflammatory cytokines, as an indirect means of regulating MYC overexpression in AML. Furthermore, we highlight Food and Drug Administration (FDA)-approved drugs for AML, and the results of preclinical and clinical studies on novel agents that have been or are currently being tested for efficacy and tolerability in AML therapy. Overall, this review summarizes our current knowledge of the molecular processes that promote leukemogenesis, as well as the various agents that intervene in specific pathways and directly or indirectly modulate c-MYC to disrupt AML pathogenesis and drug resistance.

Tumor-Specific Effector CD8+ T Cells That Can Establish Immunological Memory in Humans after Adoptive Transfer Are Marked by Expression of IL7 Receptor and c-myc

The optimal T-cell attributes for adoptive cancer immunotherapy are unclear. Recent clinical trials of ex vivo-expanded tumor-infiltrating lymphocytes indicated that differentiated T effector cells can elicit durable antitumor responses in some patients with cancer, with their antitumor activity tightly correlated with their persistence in the host. Thus, there is great interest in the definition of intrinsic biomarkers that can predict the conversion of short-lived tumor antigen-specific T effector cells into long-lived T memory cells. Long-term persistence of ex vivo-expanded tumor-specific CD8+ T effector clones has been reported in refractory metastatic melanoma patients after adoptive T-cell transfer. By using highly homogeneous clone populations from these preparations, we performed a comparative transcriptional profiling to define preinfusion molecular attributes that can be ascribed to an effector-to-memory transition. Through this route, we discovered that preinfusion T-cell clones that expressed the IL7 receptor (IL7R) and c-myc were more likely to persist longer after adoptive transfer to patients. The predictive value of these two biomarkers was strengthened by using IL7R protein, IL7-induced pSTAT5, and c-myc mRNA expression to prospectively identify human tumor-specific T effector clones capable of engraftment into immunodeficient mice. Overall, our findings reveal IL7R and c-myc expression as intrinsic biomarkers that can predict the fate of CD8+ T effector cells after adoptive transfer.

The activities of MYC, MNT and the MAX-interactome in lymphocyte proliferation and oncogenesis

The MYC family of proteins plays essential roles in embryonic development and in oncogenesis. Efforts over the past 30 years to define the transcriptional activities of MYC and how MYC functions to promote proliferation have produced evolving models of MYC function. One picture that has emerged of MYC and its partner protein MAX is of a transcription factor complex with a seemingly unique ability to stimulate the transcription of genes that are epigenetically poised for transcription and to amplify the transcription of actively transcribed genes. During lymphocyte activation, MYC is upregulated and stimulates a pro-proliferative program in part through the upregulation of a wide variety of metabolic effector genes that facilitate cell growth and cell cycle progression. MYC upregulation simultaneously sensitizes cells to apoptosis and activated lymphocytes and lymphoma cells have pro-survival attributes that allow MYC-driven proliferation to prevail. For example, the MAX-interacting protein MNT is upregulated in activated lymphocytes and was found to protect lymphocytes from MYC-dependent apoptosis. Here we review the activities of MYC, MNT and other MAX interacting proteins in the setting of T and B cell activation and oncogenesis. This article is part of a Special Issue entitled: Myc proteins in cell biology and pathology.

Characterization of an interleukin-7-dependent thymic cell line derived from a p53(-/-) mouse

In order to study the response of T cells to IL-7, we aimed to generate an IL-7-dependent thymocyte line. CD4(-)CD8(-) thymocytes from a p53(-)/(-) mouse were continuously propagated in interleukin-7 (IL-7), and after 2 months there developed an immortal line termed "D1." The D1 line has retained a stable dependency on IL-7. Withdrawal of IL-7 from D1 cells induced arrest in G1 phase of the cell cycle, followed by apoptosis. In addition to IL-7, several other cytokines that employ gamma(c) as part of their receptor were also capable of stimulating D1 cell survival and proliferation. Gene induction by IL-7 was analyzed in D1 cells using RNase protection and array analysis and revealed a number of transcripts potentially involved in cell cycle, apoptosis and signaling.

Decreased expression of c-myc family genes in thymuses from myasthenia gravis patients

The thymus is a critical organ for the elimination of autoreactive T cells by apoptosis. We studied the expression of apoptosis-associated genes, bcl-xL, bad, caspase-3, and c-myc family genes in myasthenia gravis (MG) thymuses. We observed that the mRNA levels of myc family genes, c-myc and max, were markedly reduced in MG thymuses. These results indicate that c-myc-mediated signaling is abnormal in MG thymuses. The levels of molecules whose expressions are associated with myc, such as STAM, prothymosin-alpha, and NFkappaB, were also analyzed.

Defining the specific physiological requirements for c-Myc in T cell development

c-Myc is associated with cell growth and cycling in many tissues and its deregulated expression is causally implicated in cancer, particularly lymphomagenesis. However, the contribution of c-Myc to lymphocyte development is unresolved. We show here that the formation of normal lymphocytes by c-Myc-/- cells is selectively defective. c-Myc-/- cells are inefficient, in an age-dependent manner, at populating the thymus, and subsequent thymocyte maturation is ineffective: they fail to grow and proliferate normally at the late double-negative (DN) CD4-CD8- stage. Because N-Myc expression in thymocytes usually declines at the late DN stage, these results confirm that the nonredundant contributions of Myc family members to development are related to their distinct patterns of developmental gene expression.

Thymic and intestinal intraepithelial T lymphocyte development are each regulated by the gammac-dependent cytokines IL-2, IL-7, and IL-15

Both thymic and extrathymic T lineage development are characterized by cytokine-dependent regulation of complex proliferative, differentiative, and anti-apoptotic processes. The role of the gammac-dependent cytokines in this program has been interpreted as limited to the activity of IL-7. However, through the analysis of double knock-out mice, which lack signaling through the IL-7R and other gammac-dependent cytokines, we revealed a role for IL-15 in the production of early thymic pro-T cells. Although IL-2 does not function in the production of thymocytes, thymic restoration of IL-2R expression prevented fatal autoimmunity associated with IL-2- or IL-2R-deficient mice, suggesting that IL-2R functions non-redundantly at the level of the thymus to regulate self-reactivity. Moreover, IL-2, IL-7, and IL-15 also extend their developmental effects beyond the thymus to other sites of T lymphocyte production, including the gut. Here, their redundant and non-redundant activities are directly correlated to the development of phenotypically diverse subsets of intestinal intraepithelial lymphocytes.

Interleukin-7: physiological roles and mechanisms of action

Interleukin-7 (IL-7), a product of stromal cells, provides critical signals to lymphoid cells at early stages in their development. Two types of cellular responses to IL-7 have been identified in lymphoid progenitors: (1) a trophic effect and (2) an effect supporting V(D)J recombination. The IL-7 receptor is comprised of two chains, IL-7R alpha and gamma(c). Following receptor crosslinking, rapid activation of several classes of kinases occurs, including members of the Janus and Src families and PI3-kinase. A number of transcription factors are subsequently activated including STATs, c-myc, NFAT and AP-1. However, it remains to be determined which, if any, previously identified pathway leads to the trophic or V(D)J endpoints. The trophic response to IL-7 involves protecting lymphoid progenitors from a death process that resembles apoptosis. This protection is partly mediated by IL-7 induction of Bcl-2, however other IL-7-induced events are probably also involved in the trophic response. The V(D)J response to IL-7 is partly mediated through increased production of Rag proteins (which cleave the target locus) and partly by increasing the accessibility of a target locus to cleavage through chromatin remodeling.

The role of interleukin-7 in early T-cell development

Interleukin-7 (IL-7) is a non redundant cytokine in thymic T-cell development. It binds to a dimeric receptor consisting of a specific IL-7Ralpha and a gamma-common subunit that it shares with the receptors for IL-2, 4, 9, 13 and 15. IL-7 is critical for early T-cell development but it also acts on immature B-cells and mature T-cells, and leads to secondary cytokine release. Its mechanisms of action in early T-cell development may be multiple. There is direct evidence to support a mechanistic involvement in TCR-gamma rearrangement that drives further TCR-gammadelta thymocyte commitment and maturation. There is indirect evidence for a role of IL-7 in TCR-beta rearrangement. It may however also act as a survival factor for TCR-beta rearranging thymocytes while the critical commitment selections are effected by other factors. The effects of IL-7 in fetal thymus organ culture are dose dependent, with a biphasic response: low doses of IL-7 are necessary for normal TCR-alphabeta thymocyte development but high doses block TCR-alphabeta maturation in favor of TCR-gammadelta development. A good understanding of the dose response of IL-7 in thymocyte development, mature T-cell stimulation, and of the release of secondary cytokines will be important for planning successful clinical trials with IL-7.

Interleukin-7 induces T cell proliferation in the absence of Erk/MAP kinase activity

Interleukin (IL)-7 and IL-2 are important lymphoproliferative cytokines which both use the gamma c chain as part of their respective receptors. To learn more of their signaling mechanisms a comparison was made of the patterns of intracellular tyrosine phosphorylated proteins induced by these cytokines in the murine T cell line, CT6. Several similarities were revealed in the tyrosine phosphorylated proteins induced. However, a notable subset of proteins of mainly < 60 kDa were only phosphorylated by IL-2. Characterization of the two most prominent bands of this subset, pp54 and pp42, revealed these to contain Shc and p42MAP/Erk kinase, respectively. Further studies confirmed that IL-7 was unable to induce the phosphorylation of either the p44MAP/Erk or p42MAP/Erk or activation of the kinases. Shc is involved in activation of p21ras, a key event in the signaling cascade, via p72raf and MEK, leading to MAP/Erk kinase (MAPK) activation. These data indicate that this pathway is not utilized by IL-7 and may not, therefore, be essential for cytokine-driven T cell proliferation. This possibility was supported by studies with the MEK inhibitor PD098059, which had no selective effect on CT6 proliferation induced by IL-2 as compared with IL-7, although the drug completely inhibited MAP/Erk phosphorylation induced by IL-2.

Interleukin-7. Biology and implications for dermatology

In recent years, it has become apparent that IL-7, originally characterized as a growth factor for pre-B lymphocytes, also has important implications for the skin. Keratinocytes have been shown to produce IL-7. which in turn can elicit a variety of biological responses on several cell types residing in the skin. IL-7 has been demonstrated to augment the cytolytic activity of cytotoxic T cells (CTL) and natural killer (NK) cells against various neoplastic targets including melanoma cells. Proliferation and long-term survival of murine dendritic epidermal T lymphocytes (DETC) in vitro is supported by IL-7. IL-7 also induces secretion of inflammatory cytokines by monocytes/macrophages and renders these cells to become tumoricidal against melanoma cells. Normal and malignant melanocytes respond to IL-7 with increased expression of intercellular adhesion molecule (ICAM-1). In addition, IL-7 has been shown to act as growth factor for Sezary cells, suggesting a role of keratinocyte-derived IL-7 in the pathogenesis of cutaneous T cell lymphoma. Because of the potent in vitro immunomodulatory effects of IL-7 which have been confirmed in mouse tumor models, IL-7 may become a valuable additional agent to immunotherapeutical regimens currently studied in patients with advanced melanoma. This review summarizes our present knowledge about the molecular and immunological properties of IL7 with emphasis on the effects of that cytokine within the cutaneous compartment and the potential clinical utility in dermatology.