MEK inhibitors and STAT5 inhibitors downregulate expression of CD44 in neoplastic MCs. (A) HMC-1, ROSA, and MCPV-1 cells were incubated with the MEK1/2 inhibitor RDEA119 (refametinib) (0.1-5 μM) at 37°C for 48 hours. Then, expression of CD44 was analyzed by flow cytometry. Bars represent the expression levels of CD44 (SI) as percentage of dimethyl sulfoxide (DMSO) control (Co) expressed as mean ± SD of at least 3 independent experiments. *P < .05 compared with control (Student t test). (B) ROSA^{KIT WT} and ROSA^{KIT D816V} cells were incubated with RDEA119 (0.1-5 µM) at 37°C for 24 hours. Then, cells were subjected to RNA isolation and CD44 mRNA levels were measured by qPCR. Bars represent percentage of CD44 mRNA copies relative to ABL1 mRNA levels. Results are expressed as mean ± SD of 3 independent experiments. *P < .05 compared with control (Student t test) (left). In addition, expression of CD44 was analyzed by flow cytometry. Bars represent the expression of CD44 (SI) as percentage of DMSO control (Co) expressed as mean ± SD of 4 independent experiments. *P < .05 compared with control (Student t test) (right). (C) HMC-1, ROSA, and MCPV-1 cells were incubated with the STAT5 blocker pimozide (2.5-10 μM) at 37°C for 48 hours. Then, expression of CD44 was analyzed by flow cytometry. Bars represent the expression of CD44 (SI) as percentage of DMSO control (Co) expressed as mean ± SD of 4 independent experiments. *P < .05 compared with control (Student t test).