MACROPHAGE INFLAMMATORY PROTEIN-1-ALPHA ENHANCES GROWTH FACTOR-STIMULATED PHOSPHATIDYLCHOLINE METABOLISM AND INCREASES CAMP LEVELS IN THE HUMAN GROWTH FACTOR-DEPENDENT CELL-LINE M07E, EVENTS ASSOCIATED WITH GROWTH SUPPRESSION

The immunoregulatory C-C chemokine, macrophage inflammatory protein-1 alpha (MIP-1 alpha) has suppressive activity on proliferation of stem cells and early subsets of myeloid progenitor cells. A receptor for C- C chemokines that binds MIP-1 alpha has been characterized, cloned, an d shown to be related structurally to neuropeptide receptors that coup le through G-proteins to phospholipase-C and adenyl cyclase. Yet, very little information on the intracellular mechanisms of action of MIP-1 alpha is available. We show here that the human factor-dependent cell line M07e is responsive to the cell cycle-suppressive effects of MIP- 1 alpha, has specific membrane-binding sites for MIP-1 alpha, and that treatment of these cells with this chemokine increases the phosphatid ylcholine (PC) and phosphocholine turnover rates in cells that are syn ergistically stimulated by the combination of granulocyte-macrophage c olony-stimulating factor and steel factor but not by these factors act ing singly. Additionally, MIP-1 alpha treatment induces a dose- and ti me-dependent increase in intracellular cAMP levels in M07e cells. Both exogenous PC and dibutyryl cAMP were found to suppress the proliferat ion of M07e colony-forming cells to a level similar to that of MIP-1 a lpha, further implicating cAMP and PC metabolism in MIP-1 alpha-induce d M07e suppression. RANTES, a related chemokine, with weak or incomple te binding to the cloned MIP-1 alpha receptor, did not suppress M07e c olony-forming cells, nor did it increase intracellular cAMP levels, bu t it did enhance growth factor-induced PC turnover, further supporting the involvement of cAMP in MIP-1 alpha suppression while demonstratin g that increased PC turnover alone is not sufficient for suppression. These findings support the idea that the human MIP-1 alpha receptor is coupled to phospholipid and cAMP metabolism in a manner similar to ot her 7-transmembrane, C-protein-linked receptors and suggest that a pho sphatidylcholine hydrolytic cycle and an associated increase in cAMP a re part of the mechanisms of action of MIP-1 alpha.