System for F-box hormone receptor regulated protein expression in mammalian cells

1. A system for F-box hormone receptor regulated protein expression, said system comprising:

a silencing nucleic acid molecule comprising a first promoter and an shRNA operably linked to the first promoter, wherein the shRNA silences expression of a target protein; and

an expression nucleic acid molecule comprising a second promoter, an F-box hormone receptor operably linked to the second promoter, and a nucleic acid molecule encoding a fusion protein comprising an auxin induced degradation (AID) degron fused to the target protein, wherein the nucleic acid molecule encoding the fusion protein is operably linked to the second promoter.

2. The system of claim 1 , wherein the first promoter is an RNA polymerase III promoter.

3. The system of claim 1 , wherein the first promoter is a U6 promoter.

4. The system of claim 1 , wherein the shRNA targets the 3′-UTR of the target protein.

5. The system of claim 1 , wherein the shRNA targets a coding region of the target protein.

6. The system of claim 1 , wherein the fusion protein is resistant to silencing by the shRNA.

7. The system of claim 1 , wherein the second promoter is an RNA polymerase II promoter.

8. The system of claim 1 , wherein the F-box hormone receptor is codon-optimized for expression in mammalian cells.

9. The system of claim 1 , wherein the F-box hormone receptor is an auxin receptor.

10. The system of claim 1 , wherein the F-box hormone receptor is Transport Inhibitor Response 1 (TIR1).

11. The system of claim 1 , wherein the F-box hormone receptor is a chimeric F-box hormone receptor.

12. The system of claim 1 , wherein the fusion protein comprises a target protein fused to the amino-terminus of the auxin induced degradation (AID) degron.

13. The system of claim 1 , wherein the fusion protein comprises a target protein fused to the carboxyl-terminus of the auxin induced degradation (AID) degron.

14. The system of claim 1 , wherein the expression nucleic acid molecule further encodes:

a selectable marker operably linked to the second promoter.

15. The system of claim 14 , wherein the expression nucleic acid molecule further encodes:

a first self-cleaving peptide between the F-box hormone receptor and the fusion protein and a second self-cleaving peptide between the fusion protein and the selectable marker.

16. A vector comprising the system of claim 1 , wherein the silencing nucleic acid molecule is coupled directly or indirectly to the expression nucleic acid molecule.

17. A mammalian cell infected with the vector of claim 16 .

18. A method for F-box hormone receptor regulated protein degradation in a mammalian host cell comprising:

providing a mammalian host cell;

introducing the system of claim 1 into the mammalian host cell to produce a transgenic mammalian host cell;

culturing said transgenic mammalian host cell under conditions that result in (i) silencing expression of the target protein and (ii) expression of the fusion protein; and

contacting said transgenic mammalian host cell with a molecule that binds the F-box hormone receptor so that said fusion protein undergoes degradation.

19. A method for F-box hormone receptor regulated target protein degradation in a mammalian host cell comprising:

providing a mammalian host cell;

infecting, into the mammalian host cell, a first lentiviral vector comprising (i) a first silencing nucleic acid molecule comprising a primary first promoter and a first shRNA operably linked to the primary first promoter, wherein the first shRNA silences expression of a first target protein and (ii) a first expression nucleic acid molecule comprising a primary second promoter, a Transport Inhibitor Response 1 (TIR1) receptor operably linked to the primary second promoter, and a nucleic acid molecule encoding a first fusion protein comprising an auxin-induced degradation (AID) degron fused to a first target protein, wherein the nucleic acid molecule encoding the first fusion protein is operably linked to the primary second promoter;

infecting, into the mammalian host cell, a second lentiviral vector comprising (i) a second silencing nucleic acid molecule comprising a secondary first promoter and a second shRNA operably linked to the secondary first promoter, wherein the second shRNA silences expression of a second target protein and (ii) a second expression nucleic acid molecule comprising a secondary second promoter, a Coronatine Insensitive 1 (COI1 receptor operably linked to the secondary second promoter, and a nucleic acid molecule encoding a second fusion protein comprising a jasmonate ZIM-domain (JAZ) degron fused to a second target protein, wherein the nucleic acid molecule encoding the second fusion protein is operably linked to the secondary second promoter;

culturing said infected mammalian host cell under conditions that result in (i) silencing expression of the first and second target proteins and (ii) expression of the first and second fusion proteins;

contacting said infected mammalian host cell with a molecule that binds the TIR1 receptor so that said first fusion protein undergoes degradation; and

contacting said infected mammalian host cell with a molecule that binds the COI1 receptor so that said second fusion protein undergoes degradation.

20. The system of claim 1 , wherein the auxin induced degradation (AID) degron comprises amino acids 63-109 of SEQ ID NO: 3 (AID 47 ).

21. The system of claim 1 , wherein the auxin induced degradation (AID) degron consists of amino acids 63-109 of SEQ ID NO: 3 (AID 47 ).

22. The system of claim 8 , wherein the F-box hormone receptor is a plant F-box hormone receptor.