Ectopic Expression of Lin28 Biases Myeloid Differentiation to Promote an Immature Mast Cell State and Is Implicated in Aggressive Mastocytosis

Dysregulated mast cell development leads to systemic mastocytosis, a clinically variable but often devastating family of hematologic disorders. Lin28 is a heterochronic gene and pluripotency factor implicated in many types of malignancy, and prior studies suggest that Lin28 expression can restore a fetal hematopoietic program in adult mice. However, the role of Lin28 in hematologic malignancy remains controversial. In our study, we induced expression of Lin28 in adult mice using a doxycycline-responsive transgenic system. Lin28 induction caused marked mast cell accumulation in target organs such as the skin and peritoneal cavity. In vitro assays revealed a skewing of myeloid commitment in Lin28-expressing hematopoietic progenitors, with increased levels of Lin28 in common myeloid progenitors and basophil-mast cell progenitors altering gene expression patterns to favor cell fate choices that enhance mast cell specification. In addition, Lin28-induced mast cells appeared phenotypically and functionally immature, and in vitro assays suggested a slowing of mast cell terminal differentiation in the context of Lin28 upregulation. Finally, interrogation of human mast cell leukemia samples revealed upregulation of LIN28 in abnormal mast cells from patients with aggressive systemic mastocytosis (ASM). This work identifies Lin28 as a novel regulator of innate immune function and a new protein of interest in mast cell disease.