K-RAS and STAT5 upregulate expression of CD44 in neoplastic MCs. (A) HMC-1.2 (left) and ROSA^{KIT WT} (right) cells were transduced with lentiviral vectors encoding K-RAS WT or oncogenic K-RAS G12V as described in the text. Then, expression of CD44 was analyzed by flow cytometry. Bars represent the expression of CD44 as SI (MFI produced by CD44 antibody/MFI of the isotype-control antibody). *P < .05 compared with empty vector control (Student t test). (B) ROSA^{KIT WT} cells transduced with lentiviral vectors endcoding K-RAS WT or oncogenic K-RAS G12V 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 CD44 levels (SI) as percentage of DMSO control (Co) expressed as mean ± SD of 4 independent experiments. *P < .05 compared with control (Student t test). (C) HMC-1.2 (left) and ROSA^{KIT WT} (right) cells were transduced with an shRNA against STAT5 as described in the text. Then, expression of CD44 was analyzed by flow cytometry at day 4 after transduction. Bars represent the expression CD44 as SI. *P < .05 compared with control (Co) shRNA (Student t test). (D) HMC-1.2 (left) and ROSA^{KIT WT} (right) cells were transduced with lentiviral vectors encoding STAT5 WT or oncogenic STAT5 S710F as described in the text. Then, expression of CD44 was analyzed by flow cytometry. Bars represent the expression CD44 as SI. *P < .05 compared with empty vector control (Student t test).