Large changes in NAD levels associated with CD38 expression during HL-60 cell differentiation

NAD is an important cofactor involved in multiple metabolic reactions and as a substrate for several NAD-dependent signalling enzymes. One such enzyme is CD38 which, alongside synthesising Ca2+-releasing second messengers and acting as a cell surface receptor, has also been suggested to play a key role in NAD+ homeostasis. CD38 is well known as a negative prognostic marker in B-CLL but the role of its enzymatic activity has not been studied in depth to date. We have exploited the HL-60 cell line as a model of inducible CD38 expression, to investigate CD38-mediated regulation intracellular NAD+ levels and the consequences of changes in NAD+ levels on cell physiology. Intracellular NAD+ levels fell with increasing CD38 expression and this was reversed with the CD38 inhibitor, kuromanin confirming the key role of CD38 in NAD+ homeostasis. We also measured the consequences of CD38 expression during the differentiation on a number of functions linked to NAD+ and we show that some but not all NAD+-dependent processes are significantly affected by the lowered NAD+ levels. These data suggest that both functional roles of CD38 might be important in the pathogenesis of B-CLL.