REGULATION OF CELLULAR RETINOIC ACID-BINDING PROTEIN (CRABP-II) DURING HUMAN MONOCYTE DIFFERENTIATION IN-VITRO

Cellular retinoic acid binding proteins (CRABP) are low molecular weig ht proteins whose precise function remains unknown. They bind retinoid s and may thereby modulate the intracellular steady-state concentratio n of retinoids. Whereas CRABP I is ubiquitously expressed, CRABP II is mainly detected in various cell types of the skin. By representative difference analysis we found that CRABP II is also strongly expressed in human monocyte derived macrophages (MAC) but not in freshly isolate d monocytes (MO). The CRABP II mRNA was gradually upregulated during d ifferentiation from MO to MAC in the presence of 2% serum. Adherence, which is important for MO differentiation, induced CRABP II expression , but the addition of 10(-7) M retinoic acid inhibited the upregulatio n of CRABP II expression during MO/MAC differentiation. As MO can diff erentiate along the classical pathway not only to MAC but also to dend ritic cells we analyzed the expression of CRABP II in MO-derived dendr itic cells cultured with 10% FCS, IL-4, and GM-CSF. In contrast to MAC , MO-derived dendritic cells showed an extremely low expression of CRA BP II. From these results we conclude (1) that the availability and th e metabolism of retinoids may be different in MAC compared to MO and d endritic cells and (2) that this may influence differentiation and act ivation of those cells. (C) 1998 Academic Press.