Human K+ ion EAG channels

Details Human K+ ion EAG channels Human K+ ion EAG channels

2000-10-23

2003-10-28

Kemmerer, Elizabeth (Department: 1647)

Chemistry: molecular biology and microbiology

Micro-organism, tissue cell culture or enzyme using process...

Recombinant dna technique included in method of making a...

C435S320100, C435S252300, C435S325000, C435S348000, C435S410000, C435S254100, C536S023500, C536S023100

Reexamination Certificate

active

06638736

ABSTRACT:

The present invention relates to a novel human K
+
ion channel, to nucleic acid molecules encoding the same and to vectors comprising said nucleic acid molecules. The invention additionally relates to antibodies specifically directed to the novel K
+
ion channel and to pharmaceutical compositions and diagnostic kits containing at least one of the above-mentioned components. Furthermore, the present invention relates to methods of treating a disease caused by malfunction of the polypeptide of the present invention or by the (over)expression of the nucleic acid molecule of the invention comprising administering an inhibitor of said (over)expression or of ion channel function or an inhibitor abolishing said malfunction to a patient in need thereof. Methods of devising drugs for treating or preventing the above-mentioned disease, methods of inhibiting cell proliferation and methods of prognosing cancer are additional embodiments comprised by the present invention. The invention also envisages specific antisense or gene therapies on the basis of the nucleic acid molecule of the invention for inhibiting undesired cellular proliferation, for example, in connection with cancer or in neurodegenerative diseases.
Potassium channels are a relevant factor in the regulation of the resting potential of cells, and this has been regarded as their major role in excitable and non-excitable tissues. On the other hand, the explanation for their ubiquitous presence and the impressive variability in their properties remains elusive. A reasonable hypothesis is that potassium channels are present in all cell types because they have in addition some “housekeeping” role, for example in cell proliferation
1
. Their implication in the regulation of the cell division cycle has been tested repeatedly, and some experimental evidence has been presented
2,3
. However, especially since both depolarization and hyperpolarization of the membrane potential during cell cycle have been reported as depending on cell type
1,4
, there is no general model to explain the function of potassium channels in cell cycle. Two mechanisms have been proposed to explain the role of K
+
channels: they either influence the intracellular Ca
2+
concentration, or control cell volume (17, 18). Both mechanisms would indirectly influence cell proliferation. A member of the eag family has also been proposed to be preferentially expressed in cancer cells (19) Several potassium channel blockers have been tested for their capability to block cancer cell proliferation, and some of them have even been used as coadjuvants for tumor chemotherapy, specially in multidrug-resistant tumors. Nevertheless, the lack of identification of a particular potassium channel directly involved in the control of cell proliferation has, up to date, precluded the description of more specific and effective treatment protocols.
1
An “Appendix of Amendments” is enclosed showing the amendments to the Title, Specification and the claims. In the Appendix, the added portions are underscored and the deleted portions are bracketed.
Thus, the technical problem underlying the present invention was to identify a biological component within the conglomerate of potassium channels with their various effects on cell cycle division that allows an unambiguous assignment to cellular proliferation, with a specific view to human cellular proliferation. The solution to said technical problem is achieved by providing the embodiments characterized in the claims.
Accordingly, the present invention relates to a nucleic acid molecule comprising a nucleic acid molecule encoding a (poly)peptide having a function of the human K
+
ion eag channel which is
(a) a nucleic acid molecule comprising a nucleic acid molecule encoding the polypeptide having the amino acid sequence of SEQ ID: No 3 or 4;
(b) a nucleic acid molecule comprising the nucleic acid molecule having the DNA sequence of SEQ ID: No 13 or 14;
(c) a nucleic acid molecule hybridizing to the complementary strand of a nucleic acid molecule of (a) or (b); or
(d) a nucleic acid molecule being degenerate to the sequence of the nucleic acid molecule of (c).
The nucleic acid molecule of the invention encodes a (poly)peptide which is or comprises the human homologues of the rat eag channel. In this regard the term “a nucleic acid molecule comprising a nucleic acid molecule encoding a (poly)peptide having a function of the human K
+
ion eag channel” may mean that said first mentioned nucleic acid molecule solely encodes said (poly)peptide. Thus, it may be identical to said second mentioned nucleic acid molecule. Alternatively, it may comprise regulatory regions or other untranslated regions. In a further embodiment, said first mentioned nucleic acid may comprise heterologous nucleic acid which may encode heterologous proteinaceous material thus giving rise, e.g., to fusion proteins. It is further to be noted that the DNA sequences of SEQ ID NO: 13 and 14 are splice variants of the nucleic acid sequence encoding the (poly)peptide of the invention. The corresponding amino acid sequences are depicted in SEQ ID NO: 3 and 4.
The term “having a function of a human K
+
ion eag channel”, as used in connection with the present invention, has the following meaning: The channel has a single channel conductance in asymmetrical potassium, at 0 mV of about 6 pS. This value clearly distinguishes the human channel from the rat channel for which a value of about 7 pS was measured. In addition or in the alternative, the above term may have the following meaning: The channel has a IC50 of about 1 mM to quinidine when expressed in Xenopus laevis oocytes, as compared to 400 &mgr;M for reag. Further, when measuring voltage-dependence of activation in high extracellular potassium using a two-electrode voltage-clamp it was found that in a conductance-voltage plot, the voltage for half-activation is shifted by about 40 mV or more to the right in the heag channel with respect to the reag channel (see FIG.
13
). On the basis of the above features, either alone or in combination, a differentiation based on function between the human ion channel of the invention and the prior art channels, in particular of the rat ion channel, is possible for the person skilled in the art without further ado. Preferably, the channel has all recited functions. The above values refer to values that are obtainable with the experimental set-up described in this specification. Alterations of experimental parameters such as the employment of a different expression system may, as is well known to the person skilled in the art, also change the above values. Yet, these embodiments are also comprized by the scope of the present invention.
The term “hybridizing” as used in accordance with the present invention relates to stringent or non-stringent hybridization conditions. Preferably, it relates to stringent conditions. Said hybridization conditions may be established according to conventional protocols described, for example, in Sambrook, “Molecular Cloning, A Laboratory Manual”, Cold Spring Harbor Laboratory (1989) N.Y., Ausubel, “Current Protocols in Molecular Biology”, Green Publishing Associates and Wiley Interscience, N.Y. (1989), or Higgins and Hames (eds) “Nucleic acid hybridization, a practical approach” IRL Press Oxford, Washington D.C., (1985). Hybridizing molecules or molecules falling under alternative (d), supra, also comprise fragments of the molecules identified in (a) or (b) wherein the nucleotide sequence need not be identical to its counterpart in SEQ ID 13 or 14, said fragments having a function as indicated above.
An example of one such stringent hybridization condition is hybridization at 4×SSC at 65° C., followed by a washing in 0.1×SSC at 65° C. for one hour. Alternatively, an exemplary stringent hybridization condition is in 50% formamide, 4×SSC at 42° C. Examples of such non-stringent hybridization conditions are 4×SSC at 50° C. or hybridization with 30-40% formamide at 42° C. Complementary strands of hybri

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