Granulocyte-macrophage colony-stimulating factor increases l-arginine transport through the induction of CAT2 in bone marrow-derived macrophages

Abstract

L-arginine transport is crucial for macrophage activation because it supplies substrate for the key enzymes nitric oxide synthase 2 and arginase I. These enzymes participate in classic and alternative activation of macrophages, respectively. Classic activation of macrophages is induced by type I cytokines, and alternative activation is induced by type II cytokines. The granulocyte macrophage colony-stimulating factor (GM-CSF), in addition to inducing proliferation and differentiation of macrophages, activates arginase I, but its action on L-arginine transport is unknown. We studied the L-arginine transporters that are active in mouse primary bone marrow-derived macrophages (BMM) and examined the effect of GM-CSF treatment on transport activities. Under basal conditions, L-arginine entered mainly through system y(+)L (>75%). The remaining transport was explained by system y(+) (<10%) and a diffusion component (10-15%). In response to GM-CSF treatment, transport activity increased mostly through system y(+) (>10-fold), accounting for about 40% of the total L-arginine transport. The increase in y(+) activity correlated with a rise in cationic amino acid transporter (CAT)-2 mRNA and protein. Furthermore, GM-CSF induced an increase in arginase activity and in the conversion of L-arginine to ornithine, citrulline, glutamate, proline, and polyamines. BMM obtained from CAT2-knockout mice responded to GM-CSF by increasing arginase activity and the expression of CAT1 mRNA, which also encodes system y(+) activity. Nonetheless, the increase in CAT1 activity only partially compensated the lack of CAT2 and L-arginine metabolism was hardly stimulated. We conclude that BMM present mainly y(+)L activity and that, in response to GM-CSF, l-arginine transport augments through CAT2, thereby increasing the availability of this amino acid to the cell.

Arginine transport in human monocytic leukemia THP-1 cells during macrophage differentiation

“…Similar results have been obtained in mouse peritoneal macrophages [19]. Moreover, while describing a case of a LPI subject, we have recently demonstrated that system y ϩ L activity is impaired in monocytes and AM but not in mesenchymal cells [20].…”

Impairment of d-alanine biosynthesis in Mycobacterium smegmatis determines decreased intracellular survival in human macrophages

“…Nonetheless, infection with M. smegmatis (Ehrt et al, 1997), maturation in culture (Martin & Edwards, 1993), and specific experimental conditions may sufficiently increase reactive intermediate levels, especially for RNI, to have bactericidal action on this micro-organism, as suggested by our inhibition studies. Activation of the arginase pathway reduces arginine availability for the NO synthase reaction in murine macrophages (Martin et al, 2006). This leads to an increase in intracellular levels of Lglutamate.…”

L-arginine metabolism and its impact on host immunity against Leishmania infection

“…The most relevant CAT member involved in MΦ functions is CAT-2, which can be expressed in two splice variants. CAT-2A is constitutively expressed in the liver and muscle cells [27], whereas the expression level CAT-2B is inducible in MΦs and strongly unregulated by IFN-γ, IFN-γ coupling with LPS, IL-4, and GM-CSF [28][29][30]. In the context of Leishmania infection, the expression and function of CAT-2B in MΦs are critical, because CAT-2B-mediated L-arginine transport potentially affects both iNOS and the arginase pathways.…”