PRRT2 and acute myeloid leukemia: Furthermore, we could show a tendency for GRK6 downregulation on a transcriptional, mRNA, and protein level in response to PMA stimulation, which is known to activate protein kinase C. Although it is questionable whether these changes are solely due to PKC activation, our findings are consistent with previous studies showing the effects of PKC activation on GRK6 expression in a human acute myeloid leukaemia HL-60 cell line [14].