JAK2 and myelofibrosis: In a study of two mouse models of thrombopoietin and constitutively active JAK2 mutant (JAKV617F)-induced myelofibrosis (88), HSP27 was found to regulate the proliferation of JAK2V617F-positive cells and interact directly with JAK2/STAT5 to protect STAT5 from dephosphorylation.