Activation of HIV-1 coreceptor (CXCR4) mediates myelosuppression.

Chemokines are cytokines that activate and induce the migration of leukocytes. Stroma-derived factor-1 (SDF-1) is a novel chemokine that blocks the entry of T-tropic HIV-1 mediated by fusin/CXCR4/LESTR (leukocyte-derived seven-transmembrane domain receptor). In this work we demonstrate that SDF-1 triggers increases in intracellular calcium and inhibits the proliferation of myeloid progenitor cell line 32D. By contrast, SDF-1 neither triggers a calcium response nor affects the proliferation of the myeloid progenitor cell line 32D-GR that is deficient in CXCR4. Responsiveness to SDF-1 was rescued by transfection of 32D-GR cells with a cDNA encoding the human CXCR4. The data indicate that SDF-1 induces myelosuppression by activation of CXCR4. The constitutive production of SDF-1 by bone marrow stromal cells argues for a major role of SDF-1 on the regulation of myelopoiesis.

Anion exchange protein in Southeast Asian ovalocytes: heterodimer formation between normal and variant subunits.

Chemical cross-linking has been used to determine the composition of the erythrocyte band 3 protein dimer in Southeast Asian ovalocytes (SAO). Individuals with SAO are heterozygous for a mutation in which residues 400-408 of band 3 are deleted. Normal and variant protein are present in equal amounts, but the SAO protein does not transport anions or bind stilbenedisulfonates with high affinity. We find that the rate constant for 35SO4(2-) efflux from SAO cells is about 50% that of normal cells, but the time course is a single exponential, indicating that there is no detectable heterogeneity in the distribution of SAO band 3 in the population of cells. Treatment of intact cells with the homobifunctional crosslinker BS3 (bis[sulfosuccinimido]suberate) produces similar amounts of covalent dimer in both normal and SAO cells. In SAO cells, copies of normal band 3 can be distinguished from SAO band 3 by treating with H2DIDS to form a crosslink between major chymotryptic fragments (60 kDa and 35 kDa) within one subunit. Successive treatment of cells with [3H]-4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonate ([3H]H2DIDS), BS3, and chymotrypsin gives 3H-labeled products that include homodimer of normal band 3 as well as products of crosslinking normal band 3 with the 60- and 35-kDa fragment of SAO band 3. The results are in semiquantitative agreement with a model in which covalent dimer forms between normal and SAO subunits with the same probability as between two normal subunits. These results indicate that the normal copy of band 3, complexed in a heterodimer with SAO band 3, reacts with H2DIDS as in normal cells.(ABSTRACT TRUNCATED AT 250 WORDS)