Methods for identifying modulators of Notch activation
The present invention is directed to methods for detecting or measuring Notch activation by observing or measuring the appearance of Notch on the cell surface or by observing or measuring Notch cleavage products that are indicative of Notch activation. The present invention is also directed to methods for detecting a molecule that modulates Notch activation by observing or measuring a change in the amount of Notch expressed on the cell surface or a change in the amount or pattern of Notch cleavage products. The present invention is also directed to a substantially purified activated heterodimeric form of Notch and components thereof and pharmaceutical compositions and kits thereof. The present invention is based, at least in part, on the discovery that Notch in its active form, i.e., the form that mediates signal transduction and that binds Notch ligands such as Delta, is a heterodimer of an about 180 kDa subunit (N EC ) and an about 110 kDa subunit (N TM ), which are tethered together through a reducing agent-sensitive linkage, in particular, a non-covalent, metal ion-dependent linkage.
1. A method for identifying a modulator of Notch activation comprising providing a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more Notch cleavage products selected from the group consisting of N EC and N TM , in which a difference in the presence or amount of said one or more cleavage products compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
2. A method for identifying a modulator of Notch activation comprising contacting a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of one or more fragments of Notch selected from the group consisting of an amino-terminal fragment of full-length Notch terminating between the epidermal growth factor-like repeat domain and the transmembrane domain of full-length Notch, and a carboxy-terminal fragment of full-length Notch with its amino terminus situated between the epidermal growth factor-like repeat domain and the transmembrane domain; in which a difference in the presence or amount of said one or more fragments compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
3. A method for identifying a modulator of Notch activation comprising contacting a cell with a candidate modulator molecule and detecting or measuring the expression by the cell of one or more fragments of Notch selected from the group consisting of Notch fragments having a molecular weight of about 270, 200, 170, 140, 110, 100, 90 and 85 kilodaltons, in which a difference in the presence or amount of said one or more fragments compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
4. A method for identifying a modulator of Notch activation comprising contacting a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of a pattern of Notch cleavage products as shown in FIG. 10A or 10 B, in which a difference in the presence or amount of said pattern compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
5. A method for identifying a modulator of Notch activation comprising contacting a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of one or more Notch fragments of about 180 kilodaltons and about 110 kilodaltons, respectively, in which a difference in the presence or amount of the fragments compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
6. A method for identifying a modulator of Notch activation comprising contacting a cell with a candidate modulator molecule and detecting or measuring the amount of the expression by the cell of a Notch heterodimer containing a reducing agent-sensitive linkage, in which a difference in the presence or amount of the heterodimer compared to a Notch cell not contacted with the candidate molecule indicates that the molecule modulates Notch activity.
7. The method according to any one of claims 1 - 6 in which the candidate modulator molecule decreases said expression, thereby being identified as a candidate inhibitor of Notch activation.
8. The method according to any one of claims 1 - 6 in which the candidate modulator molecule increases said expression, thereby being identified as a candidate agonist of Notch activation.
9. The method according to claim 1 in which the Notch cleavage products are detected by contacting a protein-containing sample from the cell with an anti-Notch antibody or a binding region thereof under conditions conducive to immunospecific binding, and separating by size any components that bind.
10. The method according to claim 6 in which the reducing agent-sensitive linkage is a non-covalent, metal ion-dependent sensitive linkage.
11. The method according to claim 2 in which the amino-terminal fragment of full-length Notch terminates between the Lin-12/Notch repeats and the transmembrane domain, and the carboxy-terminal fragment of full-length Notch has its amino terminus situated between the Lin-12/Notch repeats and the transmembrane domain.