A dose-finding study of temsirolimus and liposomal doxorubicin for patients with recurrent and refractory bone and soft tissue sarcoma.

There are few effective therapies for high-risk sarcomas. Initial chemosensitivity is often followed by relapse. In vitro, mammalian target of rapamycin (mTOR) inhibition potentiates the efficacy of chemotherapy on resistant sarcoma cells. Although sarcoma trials using mTOR inhibitors have been disappointing, these drugs were used as maintenance. We conducted a Phase I/II clinical trial to test the ability of temsirolimus to potentiate the cytotoxic effect of liposomal doxorubicin and present here the dose-finding portion of this study. Adult and pediatric patients with recurrent or refractory sarcomas were treated with increasing doses of liposomal doxorubicin and temsirolimus using a continual reassessment method for escalation, targeting a dose-limiting toxicity rate of 20%. Blood samples were drawn before and after the first dose of temsirolimus in Cycles 1 and 2 for pharmacokinetic analysis. The maximally tolerated dose combination was liposomal doxorubicin 30 mg/m(2) monthly with temsirolimus 20 mg/m(2) weekly. Hematologic toxicity was common but manageable. Dose-limiting toxicities were primarily renal. Concurrent administration of liposomal doxorubicin resulted in increased exposure to sirolimus, the active metabolite of temsirolimus. Thus, the combination of liposomal doxorubicin and temsirolimus is safe for heavily pretreated sarcoma patients. Co-administration with liposomal doxorubicin did not alter temsirolimus pharmacokinetics, but increased exposure to its active metabolite.

Interaction of hematopoietic progenitor kinase 1 with adapter proteins Crk and CrkL leads to synergistic activation of c-Jun N-terminal kinase.

Hematopoietic progenitor kinase 1 (HPK1), a mammalian Ste20-related protein kinase, is an upstream activator of c-Jun N-terminal kinase (JNK). In order to further characterize the HPK1-mediated JNK signaling cascade, we searched for HPK1-interacting proteins that could regulate HPK1. We found that HPK1 interacted with Crk and CrkL adaptor proteins in vitro and in vivo and that the proline-rich motifs within HPK1 were involved in the differential interaction of HPK1 with the Crk proteins and Grb2. Crk and CrkL not only activated HPK1 but also synergized with HPK1 in the activation of JNK. The HPK1 mutant (HPK1-PR), which encodes the proline-rich region alone, blocked JNK activation by Crk and CrkL. Dominant-negative mutants of HPK1 downstream effectors, including MEKK1, TAK1, and SEK1, also inhibited Crk-induced JNK activation. These results suggest that the Crk proteins serve as upstream regulators of HPK1. We further observed that the HPK1 mutant HPK1-KD(M46), which encodes the kinase domain with a point mutation at lysine-46, and HPK1-PR blocked interleukin-2 (IL-2) induction in Jurkat T cells, suggesting that HPK1 signaling plays a critical role in IL-2 induction. Interestingly, HPK1 phosphorylated Crk and CrkL, mainly on serine and threonine residues in vitro. Taken together, our findings demonstrate the functional interaction of HPK1 with Crk and CrkL, reveal the downstream pathways of Crk- and CrkL-induced JNK activation, and highlight a potential role of HPK1 in T-cell activation.

Hematopoietic progenitor kinase-1 (HPK1) stress response signaling pathway activates IkappaB kinases (IKK-alpha/beta) and IKK-beta is a developmentally regulated protein kinase.

Nuclear factor kappa-B (NF-kappaB) is a pleiotropic transcription factor that plays a central role in the immune and inflammatory responses, and is also involved in controlling viral transcription and apoptosis. A critical control in the activation of NF-kappaB is the phosphorylation of its inhibitory factor IkappaBs by IkappaB kinases (IKK-alpha and -beta). Here, we present experiments addressing the regulation and global expression of murine IKK-beta, and localize the IKK-beta gene to mouse chromosome 8A3-A4. IKK-beta was expressed primarily in the liver, kidney and spleen, and at lower levels in the other adult tissues. While IKK-beta was expressed ubiquitously throughout the mouse embryo at 9.5 days, its expression began to be localized to the brain, neural ganglia, neural tube, and liver in the 12.5-day's embryo. At 15.5 days, the expression of IKK-beta was further restricted to specific tissues of the embryo, suggesting that IKK-beta is a developmentally regulated protein kinase. Interestingly, IKK-beta phosphorylated IkappaB constitutively, whereas IKK-alpha was not active in the absence of cell stimulation. Moreover, both IKK-alpha and -beta were activated by hematopoietic progenitor kinase-1 (HPK1) and MAPK/ERK kinase kinase-1 (MEKK1) specifically, suggesting that IkappaB/NF-kappaB is regulated through the HPK1-MEKK1 stress response signaling pathway.

Caspase-mediated cleavage and functional changes of hematopoietic progenitor kinase 1 (HPK1).

Activation of c-Jun N-terminal kinase (JNK) by Fas ligation is caspase-dependent, suggesting that caspases may regulate activators of the JNK pathway. Here, we report that an upstream activator of JNK, hematopoietic progenitor kinase 1 (HPK1), was cleaved during apoptosis. Cleavage of HPK1 was blocked by peptide inhibitors for caspases. HPK1 was efficiently processed by recombinant caspase 3 in vitro. A conserved caspase recognition site, DDVD (amino acids 382 - 385), was found in the HPK1 protein sequence. By testing HPK1 proteins with in vivo and in vitro cleavage assays, we showed that aspartic acid residue 385 is the target for caspases. HPK1 cleavage separated the amino N-terminal kinase domain from the carboxyl C-terminal regulatory domain, and enhanced HPK1 kinase activity. Unlike the full-length HPK1, the N-terminal cleaved product failed to bind adaptor molecules Grb2 (growth factor receptor-bound protein 2) and Crk (CT10 regulator of kinase). The C-terminal fragment, although having three proline-rich domains, bound to Grb2 and Crk less efficiently than the full-length HPK1 protein. Taken together, the cleavage of HPK1 by caspase profoundly changed its biochemical properties.

Persistent activation of c-Jun N-terminal kinase 1 (JNK1) in gamma radiation-induced apoptosis.

The c-Jun N-terminal kinases (JNK) are activated by various stimuli, including UV light, interleukin-1, tumor necrosis factor-alpha (TNF-alpha), and CD28 costimulation. Induction of JNK by TNF-alpha, a strong apoptosis inducer, implies a possible role of JNK in the regulation of programmed cell death. Present studies show that lethal doses of gamma radiation (GR) induced JNK activities at the early phase of apoptosis in Jurkat T-cells. We demonstrate that JNK1 was activated by either the T-cell activation signals, anti-CD28 monoclonal antibody plus phorbol 12-myristate 13-acetate (PMA), or the apoptosis-inducing treatment, GR; however, the induction patterns were different. In contrast to the rapid and transient JNK1 activation caused by CD28 signaling plus PMA, GR induced a delayed and persistent JNK1 activation. This implies a distinct regulatory mechanism and specific function of JNK1 in irradiated cells. The nuclear and cytosolic JNK1 activities were simultaneously increased in the irradiated cells without an evident change in the protein levels. The abilities of GR to induce JNK1 activation and DNA fragmentation were correlated. Peripheral blood lymphocytes were more sensitive to GR than Jurkat cells in JNK1 induction. The responsiveness of JNK1 to GR suggests the involvement of JNK1 in the initiation of the apoptosis process.

Interaction between c-Rel and the mitogen-activated protein kinase kinase kinase 1 signaling cascade in mediating kappaB enhancer activation.

The Rel family of transcription factors are important mediators of various cytokine stimuli such as interleukin (IL)-1, tumor necrosis factor (TNF)-alpha, and CD28 costimulation in T cell effector responses. These stimuli induce Rel family DNA-binding activity to the kappaB enhancer and CD28 response elements of many cytokine gene promoters leading to cytokine production. Consistent with the importance of Rel family induction during immune responses, c-Rel knockout mice exhibit profound defects in T cell functions including IL-2 secretion and T cell proliferative responses to CD28 plus T cell receptor costimulation. The novel protein kinases, c-Jun NH2-terminal kinases (JNKs)/stress-activated protein kinases, are also activated by TNF-alpha, IL-1, and CD28 costimulation. Because of the common regulation of c-Rel and JNK1 by these agents in T cells, we investigated the role of JNK1 in c-Rel activation. We found that MAP kinase kinase kinase (MEKK) 1, a JNK1 activator, induced transcription from the human immunodeficiency virus-1 long terminal repeat and IL-2R alpha promoters in a kappaB-dependent manner. Coexpression of IkappaBalpha, a c-Rel inhibitor, inhibited the MEKK1-induced transcriptional activity. JNK1 synergized with MEKK1 in activating transcription from a kappaB-driven heterologous promoter. Furthermore, JNK1 associated with c-Rel in vivo in Jurkat T cells by coimmunoprecipitation assays and bound directly to c-Rel in a yeast two-hybrid assay. c-Rel also competed with c-Jun in in vitro kinase assays. However, JNK1 did not phosphorylate c-Rel, NF-kappaB, and IkappaB alpha in vitro, indicating that c-Rel may serve as a docking molecule to allow JNK1 phosphorylation of certain Rel-associated proteins. Transactivation of the IL-2Ralpha and HIV-kappaB-driven promoters by c-Rel was augmented by coexpression of MEKK1. These results demonstrate the first significant role for the MEKK1 kinase cascade module in c-Rel-mediated transcription.

Human HPK1, a novel human hematopoietic progenitor kinase that activates the JNK/SAPK kinase cascade.

The c-Jun amino-terminal kinases (JNKs)/stress-activated protein kinases (SAPKs) play a crucial role in stress responses in mammalian cells. The mechanism underlying this pathway in the hematopoietic system is unclear, but it is a key in understanding the molecular basis of blood cell differentiation. We have cloned a novel protein kinase, termed hematopoietic progenitor kinase 1 (HPK1), that is expressed predominantly in hematopoietic cells, including early progenitor cells. HPK1 is related distantly to the p21(Cdc42/Rac1)-activated kinase (PAK) and yeast STE20 implicated in the mitogen-activated protein kinase (MAPK) cascade. Expression of HPK1 activates JNK1 specifically, and it elevates strongly AP-1-mediated transcriptional activity in vivo. HPK1 binds and phosphorylates MEKK1 directly, whereas JNK1 activation by HPK1 is inhibited by a dominant-negative MEKK1 or MKK4/SEK mutant. Interestingly, unlike PAK65, HPK1 does not contain the small GTPase Rac1/Cdc42-binding domain and does not bind to either Rac1 or Cdc42, suggesting that HPK1. activation is Rac1/Cdc42-independent. These results indicate that HPK1 is a novel functional activator of the JNK/SAPK signaling pathway.

Activation of the c-Jun N-terminal kinase pathway by a novel protein kinase related to human germinal center kinase.

The c-Jun N-terminal kinase (JNK), or stress-activated protein kinase plays a crucial role in cellular responses stimulated by environmental stress and proinflammatory cytokines. However, the mechanisms that lead to the activation of the JNK pathway have not been elucidated. We have isolated a cDNA encoding a novel protein kinase that has significant sequence similarities to human germinal center kinase (GCK) and human hematopoietic progenitor kinase 1. The novel GCK-like kinase (GLK) has a nucleotide sequence that encodes an ORF of 885 amino acids with 11 kinase subdomains. Endogenous GLK could be activated by UV radiation and proinflammatory cytokine tumor necrosis factor alpha. When transiently expressed in 293 cells, GLK specifically activated the JNK, but not the p42/44(MAPK)/extracellular signal-regulated kinase or p38 kinase signaling pathways. Interestingly, deletion of amino acids 353-835 in the putative C-terminal regulatory region, or mutation of Lys-35 in the putative ATP-binding domain, markedly reduced the ability of GLK to activate JNK. This result indicates that both kinase activity and the C-terminal region of GLK are required for maximal activation of JNK. Furthermore, GLK-induced JNK activation could be inhibited by a dominant-negative mutant of mitogen-activated protein kinase kinase kinase 1 (MEKK1) or mitogen-activated protein kinase kinase 4/SAPK/ERK kinase 1 (SEK1), suggesting that GLK may function upstream of MEKK1 in the JNK signaling pathway.

Involvement of hematopoietic progenitor kinase 1 in T cell receptor signaling.

Hematopoietic progenitor kinase 1 (HPK1), a mammalian Ste20-related serine/threonine protein kinase, is a hematopoietic-specific upstream activator of the c-Jun N-terminal kinase. Here, we provide evidence to demonstrate the involvement of HPK1 in T cell receptor (TCR) signaling. HPK1 was activated and tyrosine-phosphorylated with similar kinetics following TCR/CD3 or pervanadate stimulation. Co-expression of protein-tyrosine kinases, Lck and Zap70, with HPK1 led to HPK1 activation and tyrosine phosphorylation in transfected mammalian cells. Upon TCR/CD3 stimulation, HPK1 formed inducible complexes with the adapters Nck and Crk with different kinetics, whereas it constitutively interacted with the adapters Grb2 and CrkL in Jurkat T cells. Interestingly, HPK1 also inducibly associated with linker for activation of T cells (LAT) through its proline-rich motif and translocated into glycolipid-enriched microdomains (also called lipid rafts) following TCR/CD3 stimulation, suggesting a critical role for LAT in the regulation of HPK1. Together, these results identify HPK1 as a new component of TCR signaling. T cell-specific signaling molecules Lck, Zap70, and LAT play roles in the regulation of HPK1 during TCR signaling. Differential complex formation between HPK1 and adapters highlights the possible involvement of HPK1 in multiple signaling pathways in T cells.