A case report of concurrent embryonal rhabdomyosarcoma and diffuse large B-cell lymphoma in an adult without identifiable cancer predisposition.

BACKGROUND: Diffuse large B-cell lymphoma (DLBCL) is the most common form of non-Hodgkin lymphoma. Rhabdomyosarcoma, the most common soft tissue sarcoma of childhood. makes up less than 1% of solid malignancies in adults with around 400 new cases each year in the United States. They have not previously been reported concurrently. CASE PRESENTATION: A 37 year old woman presented with painful enlarging leg mass. Biopsy of the mass was consistent with embryonal rhabdomyosarcoma. Staging imaging revealed a PET avid anterior mediastinal lymph node. Excisional biopsy of this mass was consistent with diffuse large B-cell lymphoma. Hybridization capture-based next-generation DNA sequencing did not reveal shared somatic tumor mutations. Germline analysis did not show identifiable aberrations of TP53 or other heritable cancer susceptibility genes. She was treated with a personalized chemotherapy regimen combining features of R-CHOP and Children's Oncology Group ARST 0331. CONCLUSIONS: This case illustrates a unique clinical entity successfully treated with a personalized chemotherapeutic regimen.

Activity of a selective inhibitor of nuclear export, selinexor (KPT-330), against AML-initiating cells engrafted into immunosuppressed NSG mice.

Currently available combination chemotherapy for acute myeloid leukemia (AML) often fails to result in long-term remissions, emphasizing the need for novel therapeutic strategies. We reasoned that targeted inhibition of a prominent nuclear exporter, XPO1/CRM1, could eradicate self-renewing leukemia-initiating cells (LICs) whose survival depends on timely XPO1-mediated transport of specific protein and RNA cargoes. Using an immunosuppressed mouse model bearing primary patient-derived AML cells, we demonstrate that selinexor (KPT-330), an oral antagonist of XPO1 that is currently in clinical trials, has strong activity against primary AML cells while sparing normal stem and progenitor cells. Importantly, limiting dilution transplantation assays showed that this cytotoxic activity is not limited to the rapidly proliferating bulk population of leukemic cells but extends to the LICs, whose inherent drug resistance and unrestricted self-renewal capacity has been implicated in the difficulty of curing AML patients with conventional chemotherapy alone.

Antileukemic activity of nuclear export inhibitors that spare normal hematopoietic cells.

Drugs that target the chief mediator of nuclear export, chromosome region maintenance 1 protein (CRM1) have potential as therapeutics for leukemia, but existing CRM1 inhibitors show variable potencies and a broad range of cytotoxic effects. Here, we report the structural analysis and antileukemic activity of a new generation of small-molecule inhibitors of CRM1. Designated selective inhibitors of nuclear export (SINE), these compounds were developed using molecular modeling to screen a small virtual library of compounds against the nuclear export signal (NES) groove of CRM1. The 2.2-Å crystal structure of the CRM1-Ran-RanBP1 complex bound to KPT-251, a representative molecule of this class of inhibitors, shows that the drug occupies part of the groove in CRM1 that is usually occupied by the NES, but penetrates much deeper into the groove and blocks CRM1-directed protein export. SINE inhibitors exhibit potent antileukemic activity, inducing apoptosis at nanomolar concentrations in a panel of 14 human acute myeloid leukemia (AML) cell lines representing different molecular subtypes of the disease. When administered orally to immunodeficient mice engrafted with human AML cells, KPT-251 had potent antileukemic activity with negligible toxicity to normal hematopoietic cells. Thus, KPT-SINE CRM1 antagonists represent a novel class of drugs that warrant further testing in AML patients.

The RING domains of the promyelocytic leukemia protein PML and the arenaviral protein Z repress translation by directly inhibiting translation initiation factor eIF4E.

The promyelocytic leukemia protein (PML) is a mammalian regulator of cell growth which is characteristically disrupted in acute promyelocytic leukemia and by a variety of viruses. PML contains a RING domain which is required for its growth-suppressive and antiviral properties. Although normally nuclear, in certain pathogenic conditions, including arenaviral infection, PML is relocated to the cytoplasm, where its functions are poorly understood. Here, we observe that PML and arenavirus protein Z use regions around the first zinc-binding site of their respective RING domains to directly interact, with sub-micromolar affinity, with the dorsal surface of translation initiation factor eIF4E, representing a novel mode of eIF4E recognition. PML and Z profoundly reduce the affinity of eIF4E for its substrate, the 5' 7-methyl guanosine cap of mRNA, by over 100-fold. Association with the dorsal surface of eIF4E and direct antagonism of mRNA cap binding by PML and Z lead to direct inhibition of translation. These activities of the RING domains of PML and Z do not involve ubiquitin-mediated protein degradation, in contrast to many RINGs which have been observed to do so. Although PML and Z have well characterized physiological functions in regulation of growth and apoptosis, this work establishes the first discrete biochemical mechanism which underlies the biological activities of their RING domains. Thus, we establish PML and Z as translational repressors, with potential contributions to the pathogenesis of acute promyelocytic leukemia and variety of viral infections.

PML RING suppresses oncogenic transformation by reducing the affinity of eIF4E for mRNA.

The promyelocytic leukemia protein PML is organized into nuclear bodies which mediate suppression of oncogenic transformation and of growth. The biochemical functions of PML bodies are unknown, despite their involvement in several human disorders. We demonstrate that eukaryotic initiation factor 4E (eIF4E) directly binds the PML RING, a domain required for association with bodies and for suppression of transformation. Nuclear eIF4E functions in nucleocytoplasmic transport of a subset of transcripts including Cyclin D1. Present studies indicate that some PML requires the evolutionarily older eIF4E protein for association with nuclear bodies. Further more, PML RING modulates eIF4E activity by drastically reducing its affinity for its substrate, 5' m(7)G cap of mRNA. We demonstrate that eIF4E requires cap binding for transport of Cyclin D1 mRNA and subsequent transformation activity. Additionally, PML reduces the affinity of eIF4E for m(7)G mRNA cap, causing a reduction in Cyclin D1 protein levels and consequent transformation inhibition. PML is the first factor shown to modulate nuclear eIF4E function. These findings provide the first biochemical framework for understanding the transformation suppression activity of PML.

D/H amide kinetic isotope effects reveal when hydrogen bonds form during protein folding.

We have exploited a procedure to identify when hydrogen bonds (H-bonds) form under two-state folding conditions using equilibrium and kinetic deuterium/hydrogen amide isotope effects. Deuteration decreases the stability of equine cytochrome c and the dimeric and crosslinked versions of the GCN4-p1 coiled coil by approximately 0. 5 kcal mol-1. For all three systems, the decrease in equilibrium stability is reflected by a decrease in refolding rates and a near equivalent increase in unfolding rates. This apportionment indicates that approximately 50% of the native H-bonds are formed in the transition state of these helical proteins. In contrast, an alpha/beta protein, mammalian ubiquitin, exhibits a small isotope effect only on unfolding rates, suggesting its folding pathway may be different. These four proteins recapitulate the general trend that approximately 50% of the surface buried in the native state is buried in the transition state, leading to the hypothesis that H-bond formation in the transition state is cooperative, with alpha-helical proteins forming a number of H-bonds proportional to the amount of surface buried in the transition state.

Construction of macromolecular assemblages in eukaryotic processes and their role in human disease: linking RINGs together.

Members of the Really Interesting New Gene (RING) family of proteins are found throughout the cells of eukaryotes and function in processes as diverse as development, oncogenesis, viral replication and apoptosis. There are over 200 members of the RING family where membership is based on the presence of a consensus sequence of zinc binding residues. Outside of these residues there is little sequence homology; however, there are conserved structural features. Current evidence strongly suggests that RINGs are protein interaction domains. We examine the features of RING binding motifs in terms of individual cases and the potential for finding a universal consensus sequence for RING binding domains (FRODOs). This review examines known and potential functions of RINGs, and attempts to develop a framework within which their seemingly multivalent cellular roles can be consistently understood in their structural and biochemical context. Interestingly, some RINGs can self-associate as well as bind other RINGs. The ability to self-associate is typically translated into the annoying propensity of these domains to aggregate during biochemical characterization. The RINGs of PML, BRCA1, RAG1, KAP1/TIF1beta, Polycomb proteins, TRAFs and the viral protein Z have been well characterized in terms of both biochemical studies and functional data and so will serve as focal points for discussion. We suggest physiological functions for the oligomeric properties of these domains, such as their role in formation of macromolecular assemblages which function in an intricate interplay of coupled metal binding, folding and aggregation, and participate in diverse functions: epigenetic regulation of gene expression, RNA transport, cell cycle control, ubiquitination, signal transduction and organelle assembly.

Transition state heterogeneity in GCN4 coiled coil folding studied by using multisite mutations and crosslinking.

We have investigated the folding behavior of dimeric and covalently crosslinked versions of the 33-residue alpha-helical GCN4-p1 coiled coil derived from the leucine zipper region of the transcriptional activator GCN4. The effects of multisite substitutions indicate that folding occurs along multiple routes with nucleation sites located throughout the protein. The similarity in activation energies of the different routes together with an analysis of intrinsic helical propensities indicate that minimal helix is present before a productive collision of the two chains. However, approximately one-third to one-half of the total helical structure is formed in the postcollision transition state ensemble. For the crosslinked, monomeric version, folding occurs along a single robust pathway. Here, the region nearest the crosslink, with the least helical propensity, is structured in the transition state whereas the region farthest from the tether, with the most propensity, is completely unstructured. Hence, the existence of transition state heterogeneity and the selection of folding routes critically depend on chain topology.

Rat preputial sebocyte differentiation involves peroxisome proliferator-activated receptors.

The hallmark of sebaceous epithelial cell (sebocyte) differentiation is the accumulation of fused neutral fat droplets. Very little sebocyte differentiation occurs, however, in primary or organ culture, even upon incubating with androgens, which are required for maturation in vivo. We hypothesized that sebocyte cell culture systems lack activators of the peroxisome proliferator-activated receptors that are involved in adipocyte differentiation. We here report that activation of peroxisome proliferator-activated receptor gamma and alpha by their respective specific ligands, a thiazolidinedione and a fibrate, induced lipid droplet formation in sebocytes but not epidermal cells. Linoleic acid and carbaprostacyclin, both peroxisome proliferator-activated receptor delta and alpha ligand-activators, were more effective but less specific, stimulating lipid formation in both types of cells. Either was more effective than the combination of peroxisome proliferator-activated receptor gamma and alpha activation, suggesting that peroxisome proliferator-activated receptor delta is involved in this lipid formation. Linoleic acid 0.1 mM stimulated significantly more advanced sebocyte maturation than any other treatment, including carbaprostacyclin, which suggests a distinct role of long chain fatty acids in sebocyte differentiation. Peroxisome proliferator-activated receptor gammal mRNA was demonstrated in sebocytes, but not in epidermal cells; it was more strongly expressed in freshly dispersed than in cultured sebocytes. In contrast, peroxisome proliferator-activated receptor delta mRNA was expressed to a similarly high extent before and after culture in both sebocytes and epidermal cells. These findings are compatible with the concepts that peroxisome proliferator-activated receptor gamma1 gene expression plays a unique role in the differentiation of sebocytes, while peroxisome proliferator-activated receptor delta activation and long chain fatty acids finalize sebocyte maturation and are capable of stimulating epidermal lipid formation. These findings have implications for the development of new modalities of treatment for acne vulgaris.

Trifluoroethanol promotes helix formation by destabilizing backbone exposure: desolvation rather than native hydrogen bonding defines the kinetic pathway of dimeric coiled coil folding.

We measure the effects of low concentrations of helix-stabilizing cosolvents, including 2,2,2-trifluoroethanol (TFE), on the thermodynamics and kinetics of folding of the dimeric alpha-helical coiled coil derived from the leucine zipper region of bZIP transcriptional activator GCN4. The change in kinetic behavior upon addition of 5% (v/v) TFE indicates that it stabilizes the transition state to the same degree as the fully helical native state. However, folding rates are largely insensitive to alanine to glycine mutagenesis, indicating that the majority of helical structure is formed after the transition state. Equilibrium hydrogen isotope partitioning measurements indicate that intramolecular hydrogen bonds are not strengthened by TFE and that amide hydrogen bonds in the transition state are nearly the same strength as those in the unfolded state. Thus, the mechanism by which TFE exerts its helix-stabilizing effects can be divorced from helix formation and does not depend on the strengthening of intrahelical hydrogen bonds. Rather, TFE increases the structure of the binary alcohol/water solvent, thereby increasing the energetic cost associated with solvation of the polypeptide backbone. At low concentrations, TFE destabilizes the unfolded species and thereby indirectly enhances the kinetics and thermodynamics of folding of the coiled coil. A high degree of polypeptide backbone desolvation, and not the formation of regular helical structure and native strength hydrogen bonds, is the critical feature of the transition state for folding of this small dimeric protein.

Mechanisms of androgen induction of sebocyte differentiation.

It has been difficult to induce the expected sebocyte differentiation in vitro with dihydrotestosterone (DHT). We reasoned that our culture system lacks differentiating factors, and peroxisome proliferator-activated receptors (PPARs) were the prime candidates. We tested PPAR activators informative about diverse PPAR subtypes, with and without DHT (10(-6) M): BRL-49653 (10(-6) M, PPAR-gamma), WY-14643 (10(-6) M, PPAR-alpha), and linoleic acid (LIN, 10(-4) M, PPAR-delta). Treatments were added in serum-free medium to cultures of rat preputial sebocytes. Control, DHT, BRL and BRL + DHT treatments caused 11, 25, 66 and 80%, respectively, of preputial cell colonies to differentiate into lipid-forming colonies (LFCs) (p < 0.001). WY induced 20% and LIN over 95% LFC formation. PPAR-gamma mRNA was identified in preputial sebocytes by the RNase protection assay. These data suggest that differentiation of sebocytes is transduced by PPARs and have implications for the development of new treatments for acne.