Reduction of MAP Kinase activity by overexpression of a RAFTK dominant-negative kinase mutant. THP1 cells were stably transfected with the RAFTK^pcDNA vector control or with RAFTK^m457 dominant-negative kinase mutant. THP1 transfectants (20 × 10⁶) were stimulated with CSF-1/M-CSF (1,000 U/mL), and then cell lysates were prepared in RIPA buffer. Lysates were subjected to immunoprecipitation with anti-ERK1 and ERK2 antibodies. Immune complexes were absorbed with sepharose-A beads and then washed and subjected to in vitro kinase assay for 30 minutes. Samples were subjected to 15% SDS-PAGE and to autoradiography at −80°C.