You can use EMSA(Electrophoratic mobility shift assay) or COIP (co immuno precipitation).

Thanks a lot for your comments, Asif.

I have to use the primary cells from mouse models. I do not have enough cells for EMSA. Please elaborate how to use COIP if I do not know the transcription factor. Best

Dear Yan Zhang,

I did not try on animals. but as per general protocol An antibody for the protein of interest is incubated with a cell extract enabling the antibody to bind to the protein in solution. The antibody/antigen complex is then pulled out of the sample using protein A/G-coupled agarose beads. This isolates the protein of interest from the rest of the sample. The sample can then be separated by SDS-PAGE for western blot analysis.

Possibly any body who is good at animals molecular Biology can help you better.