Hematoxylin reduced the intracellular abundance of mutant CALR and inhibited JAK-STAT signaling. (A) Real-time polymerase chain reaction analysis of 24-hour treatment of hematoxylin in Ba/F3-MPL cell lines. Ba/F3-MPL CALR WT and the CRISPR-Cas9–generated CALR del37/del37 cell lines were treated with 20 μM of hematoxylin or equivalent amount of DMSO as the control for 24 hours before cell collection and RNA extraction (n = 4). The statistical test was conducted by a 2-tailed paired Student t test. (B) Western blot analysis of 24-hour treatment of hematoxylin in Ba/F3-MPL cell lines. Ba/F3-MPL CALR WT cells and CRISPR-Cas9–generated CALR WT/del79 and CALR del37/del37 cell lines were treated with 20 μM of hematoxylin or equivalent amount of DMSO as control for 24 hours before cell extraction and lysis. (C) Effect of time course treatment of hematoxylin on Ba/F3-MPL CALR WT, WT/del79, and del37/del37 cell lines. Hematoxylin was added at 20 μM for the indicated time before collection and cell lysis. (D) Western blot analysis of 24-hour treatment of hematoxylin in UT-7/TPO cell lines. CALR WT cell line and CRISPR-Cas9–generated CALR del58/WT cell lines were used and treated with indicated concentrations of hematoxylin. (E) Effect of multiple inhibitors on CALR protein level. All the indicated inhibitors were added for 8 hours in Ba/F3-MPL CALR del79/WT cell line. **P < .01, ***P < .001. BFA, brefeldin A; CQ, chloroquine.