| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | April 2, 2002 |
| PATENT TITLE |
Nucleic acids encoding NGF variants |
| PATENT ABSTRACT | NGF variants which have trkC-binding activity and trkC-signal inducing activity are provided. The variants optionally have trkA or trkB binding and signal induction activity. The NGF variants of the present invention are useful in the treatment of neuronal disorders. Nucleic acids and expression vectors encoding the NGF variant neurotrophins are also provided |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | April 24, 1998 |
| PATENT REFERENCES CITED |
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| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A nucleic acid comprising a nucleotide sequence encoding an NGF variant having substitutions at amino acid positions G23, H84, and V18 or V20 of SEQ ID NO: 1, so that the variant binds trkC, said variant otherwise retaining the sequence of SEQ ID NO: 1. 2. An expression vector comprising the nucleic acid of claim 1. 3. An isolated host cell comprising the nucleic acid of claim 1. 4. A method of producing an NGF variant, comprising culturing the host cell of claim 3 under conditions that allow expression of the NGF variant. 5. The method of claim 4, further comprising the steps of isolating the NGF variant. 6. The nucleic acid of claim 1, wherein V20 is substituted. 7. The nucleic acid of claim 1, wherein the NGF variant further comprises a substitution of F86. 8. The nucleic acid of claim 1, wherein the NGF variant further comprises a substitution of T81. 9. The nucleic acid of claim 1, wherein the NGF variant further comprises a substitution of T29. 10. The nucleic acid of claim 1, wherein the NGF variant is selected from the group consisting of NGF130 (SEQ ID NO:12), NGF131 (SEQ ID NO:13), NGFR2 (SEQ ID NO:18), and NGFR3 (SEQ ID NO:19). 11. The nucleic acid of claim 1, wherein the NGF variant further comprises an amino acid substitution at D16 which imparts trkB binding to the NGF variant. 12. The nucleic acid of claim 1, wherein the NGF variant further comprises a modification of a ten-amino-acid-N-terminal sequence of NGF, that further reduces or eliminates trkA binding, wherein the N-terminal amino acid sequence SerSerSerHisProllePhe is absent. 13. The nucleic acid of claim 1, wherein at least one of the amino acids in the ten-amino-acid-N-terminal sequence of the NGF variant are deleted or substituted to reduce or eliminate trkA binding. 14. The nucleic acid of claim 12, wherein the NGF variant further comprises an amino acid substitution imparting trkB binding at D16. 15. The nucleic acid of claim 1, wherein the NGF variant further comprises a deletion of amino acid R119 or A120 or both. 16. The nucleic acid of claim 15, wherein the NGF variant comprises a deletion of amino acid R118. 17. A nucleic acid comprising a nucleotide sequence encoding an NGF variant having substitutions at amino acid positions V18, V20, G23, H84 and either or both F86 or T81 of SEQ ID NO: 1, so that the variant binds trkC, said variant otherwise retaining the sequence of SEQ ID NO: 1. 18. An expression vector comprising the nucleic acid of claim 17. 19. An isolated host cell comprising the nucleic acid of claim 17. 20. A method of producing an NGF variant, comprising culturing the host cell of claim 19 under conditions that allow expression of the NGF variant. 21. The method of claim 20, further comprising the steps of isolating the NGF variant. 22. The nucleic acid of claim 17, wherein both T81 and F86 are substituted in the NGF variant. 23. The nucleic acid of claim 17, wherein the NGF variant further comprises a substitution of T29. 24. The nucleic acid of claim 17, wherein the NGF variant is selected from the group consisting of NGF126 (SEQ ID NO: 10), NGF1234 (SEQ ID NO: 9), NGF124 (SEQ ID NO: 7), NGF125 (SEQ ID NO: 8), NGF12 (SEQ ID NO: 5), NGF123 (SEQ ID NO: 6), and NGF127 (SEQ ID NO: 11). -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND 1. Technical Field This application relates to proteins which are involved in the growth, regulation or maintenance of nervous tissue, particularly neurons. In particular, it relates to NGF variants that have activities of other neurotrophic factor NT-3. NGF variants which have trkC-binding activity and trkC-signal inducing activity are provided. The variants optionally have trkA or trkB binding and signal induction activity. The NGF variants of the present invention are useful in the treatment of neuronal disorders. Nucleic acids and expression vectors encoding the NGF variant neurotrophins are also provided. 2. Introduction The survival and maintenance of differentiated function of vertebrate neurons is influenced by the availability of specific proteins referred to as neurotrophins. The neurotrophins form a highly homologous family of growth factors that are important for survival and maintenance of neurons during developmental and adult stages of the vertebrate nervous system (for review see Snider, 1994). Limited production of neurotrophins results in death of superfluous neurons (for reviews, see (1); (2)). The various neurotrophins differ functionally in their ability to support survival of distinct neuronal populations in the central and the peripheral nerve system (3), (4); (5), (80). The neurotrophin family is a highly homologous family which includes NT-3 (6), (7); (5); (8); (9); (10), nerve growth factor (NGF) (11); (12), brain-derived neurotrophic factor (BDNF) (13); (14)) and neurotrophin 4/5 (NT-4/5) ((15), (16), (17) and neurotrophin-6 (NT-6) (Barde, 1991; Gotz et al., 1994). Studies suggest that neurotrophins transduce intracellular signaling at least in part through the ligand-dependent activation of a class of tyrosine kinase-containing receptors of M.sub.r =140-145,000 known as the trks (18); (19) (21); (20) (22); (23); (24); (25); (26). Binding of the neurotrophins induces autophosphorylation of the trk receptors which triggers the subsequent steps in the signal transduction cascade (Kaplan & Stephens, 1994). Thus, the signal transduction pathway of neurotrophins is initiated by this high-affinity binding to and activation of specific tyrosine kinase receptors and subsequent receptor autophosphorylation (19); (27). Although there is some degree of cross-receptor interaction between the neurotrophins and the different trks, the predominant specificity appears to be NGF/trkA, BDNF/trkB, and NT-3/trkC while NT-4/5 appears to interact primarily with trkB as efficiently as BDNF (27); (19) (21); (25); (22); (28); (18); (28a). NGF interacts exclusively with trkA (Kaplan et al., 1991) while BDNF and NT-4/5 bind to trkB (Ip et al., 1993). TrkA and trkB can respond in vitro under certain circumstances to multiple neurotrophins (6); (23). TrkC responds exclusively to NT-3 (25); (26). NT-3 signals preferably through trkC but can also bind to trkA and trkB with lower affinity (Lamballe et al., 1991; Urfer et al., 1994) (FIG. 1). Thus, the most stringent member of the trk receptors in terms of specificity (trkC) interacts exclusively with the most promiscuous ligand (NT-3) of the neurotrophin family. However, the neuronal environment does restrict trkA and trkB in their ability to respond to non-preferred neurotrophic ligands (29). In addition to the trk family of receptors, the neurotrophins can also bind to a different class of receptor termed the p75 low affinity NGF receptor (p75; (30); (31)) which has an unknown mechanism of transmembrane signaling but is structurally related to a receptor gene family which includes the tumor necrosis factor receptor (TNFR), CD40, 0X40, and CD27 (32); (33); (34), (35); (36); (37)). The role of the gp75 in the formation of high-affinity binding sites and in the signal transduction pathway of neurotrophins is as yet unclear (for reviews see (38); (39)). An examination of the primary amino acid sequence of the neurotrophins reveals seven regions of 7-10 residues each which account for 85% of the sequence divergence among the family members. Nerve growth factor (NGF) is a 120 amino acid polypeptide homodimeric protein that has prominent effects on developing sensory and sympathetic neurons of the peripheral nervous system. NGF acts via specific cell surface receptors on responsive neurons to support neuronal survival, promote neurite outgrowth, and enhance neurochemical differentiation. NGF actions are accompanied by alterations in neuronal membranes (40), (41), in the state of phosphorylation of neuronal proteins (42), (43), and in the abundance of certain mRNAs and proteins likely to play a role in neuronal differentiation and function (see, for example (44)). Forebrain cholinergic neurons also respond to NGF and may require NGF for trophic support. (45). Indeed, the distribution and ontogenesis of NGF and its receptor in the central nervous system (CNS) suggest that NGF acts as target-derived neurotrophic factor for basal forebrain cholinergic neurons (46), (81). NT-3 transcription has been detected in a wide array of peripheral tissues (e. g. kidney, liver, skin) as well as in the central nerve system (e. g. cerebellum, hippocampus) (5); (7), (82). During development, NT-3 mRNA transcription is most prominent in regions of the central nervous system in which proliferation, migration and differentiation of neurons are ongoing (50). Supporting evidence for a role in neuronal development includes the promoting effect of NT-3 on neural crest cells (51) and the stimulation of the proliferation of oligodendrocyte precursor cells in vivo (79). NT-3 also supports in vitro the survival of sensory neurons from the nodose ganglion (NG) (7); (5), (83) and a population of muscle sensory neurons from dorsal root ganglion (DRG) (52). In addition to these in vitro studies, a recent report showed that NT-3 prevents in vivo the degeneration of adult central noradrenergic neurons of the locus coerulus in a model that resembles the pattern of cell loss found in Alzheimer's disease. Extensive mutational analyses of human NT-3 (Urfer et al., 1994) and mouse and human NGF (Ibanez et al., 1993; Shih et al., 1994) suggested the binding sites for trkC and trkA, respectively. The three-dimensional structures of several neurotrophins have been resolved by X-ray crystallography (McDonald et al., 1991; Holland et al., 1994; Robinson et al., 1995). In NGF the N-terminal residues contribute significantly to affinity for trkA (Shih et al., 1994) and provide the most important determinants for specificity (Ibanez et al., 1993; Urfer et al., 1994). Significant losses of biological activity and receptor binding were observed with purified homodimers of human and mouse NGF, representing homogenous truncated forms modified at the amino and carboxy termini (47); (48); (49). The 109 amino acid species (10-118)hNGF, resulting from the loss of the first 9 residues of the N-terminus and the last two residues from the C-terminus of purified recombinant human NGF, is 300-fold less efficient in displacing mouse [.sup.125 I]NGF from the human trkA receptor compared to (1-118)hNGF (49). It is 50- to 100-fold less active in dorsal root ganglion and sympathetic ganglion survival compared to (1-118)hNGF (48). The (1-118)hNGF has been reported to have considerably lower trkA tyrosine kinase autophosphorylation activity (49). For NT-3 it has been demonstrated that the epitope for trkC is formed by residues in the central .beta.-strand bundle region but does not include residues from non-conserved loops or the first six residues of the N-terminus (Urfer et al., 1994). However, a non-conserved .beta.-hairpin loop encompassing residues 40-49 (NGF residue numbers will be used throughout the text) has been proposed to mediate trkA/trkC specificity (Ilag et al., 1994), though this loop does not contribute to NT-3 binding to trkC (Urfer et al., 1994). The mechanism of trkC discrimination, however, is unclear, especially since the most important residue in NT-3 involved in binding to trkC, R103, is conserved in all neurotrophins. The elucidation of the structural determinants for neurotrophin specificity is important for understanding the function and evolution of this family of growth factors. Furthermore, administration of neurotrophins in models of nerve lesions have been shown to be beneficial for regeneration and survival of neurons (Sendtner et al., 1992; Yan et al., 1992). Since the neurotrophins have become candidates for therapeutics for a variety of neurodegenerative diseases, knowledge of the structural mechanism of neurotrophic specificity and function will help develop novel neurotrophin-based therapeutics. There has been some limited attempts to create chimeric or pan-neurotrophic factors. (See (53); (56); (54), (55)). Neuronal populations involved in neurodegenerative disorders may express more than one trk receptor and therefore administration of molecules with multiple specificities, such as MNTS-1 (Urfer et al., 1994) or PNT-1 (Ibanez et al., 1993) could be advantageous compared to administration of a single monospecific neurotrophin or a cocktail of monospecific neurotrophins. For example, the various members of the neurotrophin family may have different pharmacokinetics and therefore the behavior of neurotrophin cocktails could be difficult to predict or control. There is a need for neurotrophic molecules that have more than one neurotrophin activity and/or have improved pharmacokinetic properties and that are readily administered and retain effectiveness. These and other advantages are provide by the molecules and methods presented herein. SUMMARY The present invention is based in part on the discovery that certain residues that are part of the central .beta.-strand bundle of NT-3 and are not conserved among the neurotrophins can impart NT-3 trkC-binding and trkC-signal inducing activity when grafted onto NGF. Exchange of NGF residues at positions 18, 20, 23, 29, 84 and 86 by their NT-3 counterparts resulted in NGF variants that bound to trkC, while maintaining their affinity to trkA, and were able to induce autophosphorylation and differentiation of PC12 cells expressing trkC. These NGF variants show that the amino acid at position 23 (Glycine in NGF/Threonine in NT-3) is critical for trkC recognition while other residues fine tune the specificity of NT-3 for trkC. The results demonstrate the importance of non-conserved residues of the central .beta.-strand bundle region for the interaction of NT-3 with trkC and emphasize the different mechanism of specificity determination that is employed in the NT-3/trkC and NGF/trkA ligand/receptor pairs. Accordingly, NGF variants are provided that have trkC-binding and signal inducing activity. The NGF variants optionally have trkA-binding and signal induction activity and optionally have trkB-binding and signal inducing activity. In one embodiment the variant has both trkA and trkC activity. In another embodiment, the variant has trkC activity but lacks trkA activity. The amino acid sequence of the NGF variants are derived by the substitution, insertion or deletion of one or more amino acids of an NGF amino acid sequence. Preferably, the NGF is a naturally-occurring mammalian NGF. Most preferably it is a human NGF. An NGF variant will typically retain at least 75% amino acid sequence identity with the NGF parent molecule from which it is derived. Useful quantities of these NGF variants are provided using recombinant DNA techniques. It is a further aspect of the invention to provide recombinant nucleic acids encoding the NGF variants, and expression vectors and host cells containing these nucleic acids. An additional aspect of the present invention provides methods for producing the NGF variants, including methods using nucleic acid, vectors and host cells of the invention. In one embodiment a host cell transformed with an expression vector containing a nucleic acid encoding an NGF variant is cultured to allow expression of the nucleic acid to produce a recombinant NGF variant. Furthermore, methods and compositions for treating neuronal disorders of a mammal are provided, which use the NGF variants of the invention. Other aspects of the invention will become apparent from the following detailed description, the figures, and the claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic showing specificities of neurotrophin/trk receptor interactions. FIG. 2 depicts a sequence alignment of human NGF (SEQ ID NO:1) and human NT-3 (SEQ ID NO:2). Residue numbers that refer to the NGF sequence are used throughout the paper. Asterisks highlight NGF residues which were mutated in the variants analyzed in this study. Bars indicate locations of .beta.-strands in the X-ray structure of murine NGF (McDonald et al., 1991). FIG. 3A depicts a model of human NT-3 and FIG. 3B shows the crystal structure of murine NGF. The two monomers of each neurotrophin are shown in tan and gray; residue numbers in NGF gray monomer are denoted by a *. For highlighted residues, sidechain oxygen atoms are red and sidechain nitrogen atoms are blue. Residue 103 (Arg in both NGF and NT-3) is purple. NGF residues which were replaced with their NT-3 counterparts and affected binding and specificity are yellow; residues which did not affect binding and specificity are green. The first residue seen in the NGF crystal structure (residue 10) is brown. The variable .beta.-hairpin loop (residues 40-49) previously proposed to affect specificity (Ilag et al., 1994) is shown in cyan. FIGS. 4A and 4B depict tyrosine phosphorylation of trkA in PC12 cells expressing rat trkC. Cells were treated with 100 ng/ml of respective neurotrophin for 5 min. Lysates were equalized for cell protein, immunoprecipitated with an anti-trkA specific polyclonal antiserum and electrophoresed on 7.5% SDS-polyacryamide gels. Tyrosine phosphorylation was detected using an anti-phosphotyrosine mAb 4G10. NGF/P, purified NGF; NGF/U, concentrated supernatant of NGF-expressing 293 cells; NT-3/P, purified NT-3; NT-3/U, concentrated supernatant of NT-3 expressing 293 cells; 0, mock-treated 293 cells. FIGS. 4A and 4B show results from two separate experiments using the neurotrophins listed above each lane. FIGS. 5A, 5B and 5C depict tyrosine phosphorylation of trkC in PC12 cells expressing rat trkC. Cells were treated with 100 ng/ml of respective neurotrophin for 5 min. Lysates were equalized for cell protein, immunoprecipitated with an anti-trkC specific antiserum 656 and electrophoresed on 7.5% SDS-polyacryamide gels. Tyrosine phosphorylation was detected using an anti-phosphotyrosine mAb 4G10. NGF/P, purified NGF; NGF/U, concentrated supernatant of NGF-expressing 293 cells; NT-3/P, purified NT-3; NT-3/U, concentrated supernatant of NT-3 expressing 293 cells; 0, mock-treated 293 cells. FIGS. 5A, 5B and 5C show results from three separate experiments using the neurotrophins listed above each lane. |
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