Abstract
CD38 is an ectoenzyme and receptor with key physiological roles. It metabolizes NAD+ to adenosine diphosphate ribose (ADPR) and cyclic ADPR, regulating several processes including calcium signalling. CD38 is both a positive and negative prognostic indicator in leukaemia. In all-trans retinoic acid (RA)-induced differentiation of acute promyelocytic leukaemia and HL-60 cells, CD38 is one of the earliest and most prominently upregulated proteins known. CD38 overexpression enhances differentiation, while morpholino- and siRNA-induced knockdown diminishes it. CD38, via Src family kinases and adapters, interacts with a MAPK signalling axis that propels differentiation. Motivated by evidence suggesting the importance of CD38, we sought to determine whether it functions via dimerization. We created a linker based on the suicide substrate arabinosyl-2′-fluoro-2′-deoxy NAD+ (F-araNAD+), dimeric F-araNAD+, to induce homodimerization. CD38 homodimerization did not affect RA-induced differentiation. Probing the importance of CD38 further, we created HL-60 cell lines with CRISPR/Cas9-mediated CD38 truncations. Deletion of its enzymatic domain did not affect differentiation. Apart from increased RA-induced CD11b expression, ablation of all but the first six amino acids of CD38 affected neither RA-induced differentiation nor associated signalling. Although we cannot discount the importance of this peptide, our study indicates that CD38 is not necessary for RA-induced differentiation.
Highlights
CD38 is a type II transmembrane ectoenzyme and receptor with roles in numerous physiological processes and malignancies
HL-60 cells were cultured for 24 h with 1 μM retinoic acid (RA) as indicated
While a previous report indicated that CD38 is found as homodimers on the cell surface of murine B lymphocytes, our results suggest that dF-araNAD+ is able to induce an additional degree of CD38 homodimerization in HL-60 cells[31]
Summary
CD38 is a type II transmembrane ectoenzyme and receptor with roles in numerous physiological processes and malignancies. Ligation of CD38 using its ligand, CD31, or anti-CD38 monoclonal antibodies induces activation of a multitude of signalling proteins, including c-Cbl, p85 PI3K, c-Raf, and ERK, as well as secretion of cytokines such as IL-6 and IL-108,20,25–29. These clues drove us to investigate what CD38 receptor functions might contribute to RA-induced differentiation. We found that apart from an increase in CD11b in one of three lines, ablation of all but six amino acids of the wild-type protein had no effect on RA-induced differentiation, suggesting that the CD38 is not necessary for the process to occur
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