MAPK1 and acute monocytic leukemia: To determine whether ERK1 and/or ERK2 involved in LPS-induced G-CSF expression, ERK expression in THP-1 human acute monocytic leukemia cells was knocked down using shRNA clones ERK1a and ERK1b carrying two different ERK1 sequences or shRNAs ERK2a and ERK2b carrying two different ERK2 sequences.