The neutrophil elastase mutant affects viability and differentiation of the human monocytic THP-1 cell

Deficiency in neutrophils (neutropenia) caused by mutations in neutrophil elastase (NE, ELA2) has been extensively investigated. Monocytes and neutrophils are derived from a common myeloid progenitor; therefore, ELA2 mutations can also influence monocyte development. These effects have not been well described. In this study, we used the human monocytic THP-1, to carry the human wild-type and G185R mutant ELA2 gene. Growth, death, differentiation and BiP expression were evaluated in the two stable cell lines and in the wild-type THP-1 cells. Exogenous wild-type ELA2 markedly increased THP-1 differentiation, whereas G185R ELA2 was incompetent to promote THP-1 differentiation in response to all-trans retinoic acid (ATRA). Indeed, during differentiation induced by ATRA, G185R cell line showed significant cell death. Also, up-regulated BiP expression accompanied cell death in the G185R cells, suggesting that the overexpression of G185R elastase increases apoptosis through an unfolded protein response. The G185R cells treated with lithium chloride (LiCl; a Wnt signalling activator) displayed higher BiP expression but similar cell viability compared with THP1 and HNEwt/THP1 cells treated with LiCl. This suggested that Wnt signalling might increase cellular tolerance to endoplasmic reticulum stress, enabling mutant monocyte survival.