Japanese Red Cross Society

Basophils are the rarest granulocytes and play diverse roles, e.g., in protective immunity and allergic inflammatory reactions. However, the underlying molecules and mechanisms involved in basophil differentiation and functions, particularly in humans, remain largely unknown. This may be due to the lack of high-quality research tools.

We established a novel, immortalized, human basophil cell line by introducing human papillomavirus 16-E6/E7, c-MYC, and BCL-xL gene expression systems into cultured basophils, and evaluated whether this cell line is useful as a research tool, compared with KU812, which is the most commonly-used human basophil cell line.

This cell line expressed various basophil markers, including CD123, CD203c, and the high-affinity immunoglobulin (Ig)E receptor α-chain and can mature into more differentiated cells under specific culture conditions. The differentiated cells stimulated with anti-IgE antibodies showed increased CD203c expression in a dose-dependent manner, whereas the differentiated KU812 cells showed little activation after the stimulation. The established cell line also demonstrated increased sensitivity to allergic activation when stimulated with an allergen (NP-BSA) and allergen-specific IgE (anti-NP-IgE). Furthermore, histamine- and interleukin-4-releasing abilities were also confirmed. These allergic activation profiles were similar to those of basophils from healthy individuals, although the activation levels of the established cells were lower than those of basophils from highly-sensitive individuals.

These findings suggest that the established basophil cell line has substantially different characteristics from a conventional cell line and could serve as a new tool for investigating basophil differentiation and functions, as well as for testing allergic reactions.

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm driven by the BCR::ABL fusion tyrosine kinase. AMP-activated protein kinase (AMPK) plays a pivotal role in regulating cellular energy homeostasis, ensuring an adequate ATP supply for CML cell proliferation. ULK1, a well-known AMPK substrate, is a critical serine/threonine kinase in the autophagy initiation complex. ULK2, a paralog of ULK1, shares approximately 50 % amino acid sequence homology and has been reported to function complementarily with ULK1. However, emerging evidence suggests that ULK2 also has unique functions distinct from those of ULK1. Public RNA sequencing data revealed that ULK2 expression is significantly lower in hematopoietic cells compared to other tissues. To explore the function of ULK2, we performed in vitro assays using 293FT cells, which endogenously express high levels of ULK2. Mass spectrometry analysis demonstrated that ULK2 forms a stable complex with FIP200, which in turn interacts specifically with the AMPK α1 and γ1 subunits. Furthermore, shRNA-mediated knockdown of ULK2 induced AMPK activation and promoted the cytoplasmic accumulation of ULK1 and FIP200, thereby inducing autophagy in CML cells. Although autophagy typically acts as a cytoprotective mechanism, in this context, the autophagy-dependent degradation of BCR::ABL induced cell death. These findings reveal a novel regulatory axis involving ULK2, FIP200, AMPK, and autophagy, suggesting a unique role for ULK2 in CML pathophysiology and offering potential therapeutic insights.