Multiple myeloma is affected by multiple and heterogeneous somatic mutations in adhesion- and receptor tyrosine kinase signaling molecules

Multiple myeloma (MM) is a largely incurable plasma cell malignancy with a poorly understood and heterogeneous clinical course. To identify potential, functionally relevant somatic mutations in MM, we performed whole-exome sequencing of five primary MM, corresponding germline DNA and six MM cell lines, and developed a bioinformatics strategy that also integrated published mutational data of 38 MM patients. Our analysis confirms that identical, recurrent mutations of single genes are infrequent in MM, but highlights that mutations cluster in important cellular pathways. Specifically, we show enrichment of mutations in adhesion molecules of MM cells, emphasizing the important role for the interaction of the MM cells with their microenvironment. We describe an increased rate of mutations in receptor tyrosine kinases (RTKs) and associated signaling effectors, for example, in EGFR, ERBB3, KRAS and MAP2K2, pointing to a role of aberrant RTK signaling in the development or progression of MM. The diversity of mutations affecting different nodes of a particular signaling network appears to be an intrinsic feature of individual MM samples, and the elucidation of intra- as well as interindividual redundancy in mutations that affect survival pathways will help to better tailor targeted therapeutic strategies to the specific needs of the MM patient.

Pharmacologic activation of p53-dependent and p53-independent apoptotic pathways in Hodgkin/Reed-Sternberg cells

The status of the p53 pathway in classical Hodgkin lymphoma (cHL) remains unclear, and a lack of proven TP53 mutations contrasts with often high expression levels of p53 protein. In this study, we demonstrate that pharmacologic activation of the p53 pathway with the murine double minute 2 (MDM2) antagonist nutlin-3 in Hodgkin lymphoma-derived cell lines leads to effective apoptosis induction and sensitizes the cells to other anticancer drugs. Cells with mutant p53 are resistant to nutlin-3, but sensitive to geldanamycin, a pharmacologic inhibitor of heat shock 90 kDa protein (HSP90), indicating that HSP90 inhibition can induce apoptosis in a p53-independent manner. Conversely, cells with defects in the HSP90/nuclear factor-kappa B pathway expressing wild-type p53 are more resistant to geldanamycin, but still sensitive to nutlin-3. Our results suggest that selective activation of p53 by MDM2 antagonists as a single agent or in combination with conventional chemotherapeutics and/or inhibitors of p53-independent survival pathways may offer effective treatment options for patients with cHL. Importantly, because nutlins and HSP90 inhibitors are non-genotoxic agents, their use might offer a means to reduce the genotoxic burden of current chemotherapeutic regimens.

[Heat shock protein 90 alpha und beta are overexpressed in multiple myeloma cells and critically contribute to survival]

HSP90's are overexpressed in different cancer types and they probably are required to sustain aberrant signalling in malignant cells. Recently, pharmacological inhibition of HSP90 was found to suppress growth of myeloma cell lines and in primary myeloma cells. Therefore, we wanted to investigate the role of HSP90alpha and HSP90beta in the pathogenesis of malignant myeloma (MM) in more detail. Immunohistochemistry was employed to examine the expression of HSP90alpha and HSP90beta in MM. The importance of HSP90 for survival of MM -cells was investigated by SiRNA-mediated knockdown of HSP90 and blockade of the IL-6R/STAT3 and the MAPK signaling pathways in vitro. HSP90alpha and HSP90beta were overexpressed in majority of investigated MM cases, but not in MGUS or in normal plasma cells. SiRNA-mediated knockdown of HSP90 or treatment with the novel HSP90 inhibitor 17-DMAG attenuated the levels of STAT3 and phospho-ERK and decreased the viability of MM cells. The knockdown of HSP90alpha was sufficient to induce apoptosis. This effect was strongly increased when both HSP90s were targeted, indicating a cooperation of both. HSP90 critically contributes to myeloma survival in the context of its microenvironment and therefore strengthen the potential value of HSP90 as a therapeutic target.

A highly conserved enhancer in the Dlx5/Dlx6 intergenic region is the site of cross-regulatory interactions between Dlx genes in the embryonic forebrain

Four Dlx homeobox genes, Dlx1, Dlx2, Dlx5, and Dlx6 are expressed in the same primordia of the mouse forebrain with temporally overlapping patterns. The four genes are organized as two tail-to-tail pairs, Dlx1/Dlx2 and Dlx5/Dlx6, a genomic arrangement conserved in distantly related vertebrates like zebrafish. The Dlx5/Dlx6 intergenic region contains two sequences of a few hundred base pairs, remarkably well conserved between mouse and zebrafish. Reporter transgenes containing these two sequences are expressed in the forebrain of transgenic mice and zebrafish with patterns highly similar to endogenous Dlx5 and Dlx6 expression. The activity of the transgene is drastically reduced in mouse mutants lacking both Dlx1 and Dlx2, consistent with the decrease in endogenous Dlx5 and Dlx6 expression. These results suggest that cross-regulation by Dlx proteins, mediated by the intergenic sequences, is essential for Dlx5 and Dlx6 expression in the forebrain. This hypothesis is supported by cotransfection and DNA-protein binding experiments. We propose that the Dlx genes are part of a highly conserved developmental pathway that regulates forebrain development.

In situ hybridization and reverse transcription--polymerase chain reaction studies on the expression of the GABA(C) receptor rho1- and rho2-subunit genes in avian and rat brain

The pharmacological properties of homo-oligomeric channels formed by the GABA type A receptor-like rho1 and rho2 polypeptides are very reminiscent of those of the GABA type C receptors that have been extensively characterized in the retina. Similar receptors have been reported to occur in certain brain regions of a variety of vertebrate species. We have used in situ hybridization to investigate the expression patterns of the rho1- and rho2-polypeptide genes in the brain of the 1-day-old chick (Gallus domesticus) and the adult rat (Rattus norvegicus). Our results show that in the chick both the rho1- and rho2-subunit transcripts are present in the cerebellum, the optic tectum, the epithalamus and the nucleus pretectalis. However, the two messenger RNAs are often found in different populations of cells. Thus, only the rho1-subunit gene is expressed in the deep cerebellar nuclei, the dorsal thalamus, the ectostriatum and the tractus vestibulomesencephalicus, while only the rho2-subunit gene is transcribed in the nucleus habenularis lateralis and the nucleus isthmo-opticus. In contrast, neither of the rho-polypeptide messenger RNAs can be detected by in situ hybridization in the rat central nervous system. Reverse transcription-polymerase chain reaction amplification has been used to confirm the expression of the two rho-subunit genes in the chicken brain. Surprisingly, this highly sensitive technique also revealed transcription of these genes in the rat brain. We conclude that the rho1- and rho2-subunit genes are expressed at a much higher level in the avian brain than in the rat brain and that, at least in birds, subtypes of the GABA(C) receptor exist.

Opioid receptors from a lower vertebrate (Catostomus commersoni): sequence, pharmacology, coupling to a G-protein-gated inward-rectifying potassium channel (GIRK1), and evolution

The molecular evolution of the opioid receptor family has been studied by isolating cDNAs that encode six distinct opioid receptor-like proteins from a lower vertebrate, the teleost fish Catostomus commersoni. One of these, which has been obtained in full-length form, encodes a 383-amino acid protein that exhibits greatest sequence similarity to mammalian mu-opioid receptors; the corresponding gene is expressed predominantly in brain and pituitary. Transfection of the teleost cDNA into HEK 293 cells resulted in the appearance of a receptor having high affinity for the mu-selective agonist [D-Ala2, MePhe4-Gly-ol5]enkephalin (DAMGO) (Kd = 0.63 +/- 0.15 nM) and for the nonselective antagonist naloxone (Kd = 3.1 +/- 1.3 nM). The receptor had negligible affinity for U50488 and [D-Pen2, D-Pen5]enkephalin (DPDPE), which are kappa- and delta-opioid receptor selective agonists, respectively. Stimulation of transfected cells with 1 microM DAMGO lowered forskolin-induced cAMP levels, an effect that could be reversed by naloxone. Experiments in Xenopus oocytes have demonstrated that the fish opioid receptor can, in an agonist-dependent fashion, activate a coexpressed mouse G-protein-gated inward-rectifying potassium channel (GIRK1). The identification of six distinct fish opioid receptor-like proteins suggests that additional mammalian opioid receptors remain to be identified at the molecular level. Furthermore, our data indicate that the mu-opioid receptor arose very early in evolution, perhaps before the appearance of vertebrates, and that the pharmacological and functional properties of this receptor have been conserved over a period of approximately 400 million years implying that it fulfills an important physiological role.

Structure and pharmacological properties of a molluscan glutamate-gated cation channel and its likely role in feeding behavior

We describe the isolation of a molluscan (Lymnaea stagnalis) full-length complementary DNA that encodes a mature polypeptide (which we have named Lym-eGluR2) with a predicted molecular weight of 105 kDa that exhibits 44-48% identity to the mammalian kainate-selective glutamate receptor GluR5, GluR6, and GluR7 subunits. Injection of in vitro-transcribed RNA from this clone into Xenopus laevis oocytes results in the robust expression of homo-oligomeric cation channels that can be gated by L-glutamate (EC50 = 1.2 +/- 0.3 micron) and several other glutamate receptor agonists; rank order of potency: glutamate >> kainate > ibotenate > AMPA. These currents can be blocked by the mammalian non-NMDA receptor antagonists 6,7-dinitroquinoxaline-2,3-dione, 6-cyano-7-nitroquinoxaline-2,3-dione, and 1-(4-chlorobenzoyl)piperazine-2,3-dicarboxylic acid. Ionic-replacement experiments have shown that the agonist-induced current is carried entirely by sodium and potassium ions. In situ hybridization has revealed that the Lym-eGluR2 transcript is present in all 11 ganglia of the Lymnaea CNS, including the 4-cluster motorneurons within the paired buccal ganglia. The pharmacological properties and deduced location of Lym-eGluR2 are entirely consistent with it being (a component of) the receptor, which has been identified previously on buccal motorneurons, that mediates the excitatory effects of glutamate released from neurons within the feeding central pattern generator.

Tryptophan mutants of human C5a anaphylatoxin: a fluorescence anisotropy decay and energy transfer study

Three mutants of the anaphylatoxin C5a were prepared with positions 2, 64 and 70, respectively, substituted by tryptophan. The last mutant was additionally labelled at Cys27 for fluorescence energy transfer (FET) measurements. The structural integrity and biological activity of the molecules were not affected. Fluorescence anisotropy decay (FAD) measurements showed that the rotational correlation time for tryptophan decreases in the order: [Trp2]rhC5a > [Trp64]rhC5a > [Trp70]rhC5a, indicating an increasing mobility of the side chain. Measurements of the fluorescence energy transfer from Trp70 to the 1,5-AEDANS group at Cys27 yielded a distance distribution of 2.4 +/- 0.8 nm. This value is compatible with the C-terminal chain being arranged as a slightly stretched helix pointing away from the body of the molecule.

A recombinant hybrid anaphylatoxin with dual C3a/C5a activity

By site-directed mutagenesis of a human complement factor C5a cDNA clone, we have designed a hybrid anaphylatoxin in which three amino acid residues in the C-terminal sequence of human C5a were exchanged to create the native C-terminal human C3a (hC3a) sequence Leu-Gly-Leu-Ala-Arg. This hybrid anaphylatoxin rC5a-(1-69)-LGLAR exhibited true C3a and C5a activity when tested in the guinea pig ileum contraction assay. Quantitative measurements of ATP release from guinea pig platelets revealed about 1% intrinsic C3a activity for this hybrid, while the C5a activity was essentially unchanged. Competitive binding assays confirmed that the rC5a-(1-69)-LGLAR mutant was able to displace radioiodinated rhC5a with a KI of approx. 40 nM and hC3a with a KI of approx. 3.7 microM from guinea pig platelets. Since the C-termini of both human C3a and C5a anaphylatoxins are known to interact with their respective receptors, we conclude that the same peptidic sequence, LGLAR, is able to bind to and activate two different receptors, the C3a receptor as well as the C5a receptor. This clone provides a novel tool for the identification of further receptor-binding residues in both anaphylatoxins, since any mutants may be tested for altered C3a and C5a activity simultaneously.