Progranulin (pgrn; granulin-epithelin precursor, PC-cell-derived growth factor, or acrogranin) is a multifunctional secreted glycoprotein implicated in tumorigenesis, development, inflammation, and repair. It is highly expressed in macrophage and monocyte-derived dendritic cells. Here we investigate its regulation in myeloid cells. All-trans retinoic acid (ATRA) increased pgrn mRNA levels in myelomonocytic cells (CD34 ϩ progenitors; monoblastic U-937; monocytic THP-1; progranulocytic HL-60; macrophage RAW 264.7) but not in nonmyeloid cells tested. Interleukin-4 impaired basal expression of pgrn in U-937. Differentiation agents DMSO, and, in U-937 only, phorbol ester [phorbol 12-myristate,13-acetate (PMA)] elevated pgrn mRNA expression late in differentiation, suggestive of roles for pgrn in more mature terminally differentiated granulocyte/monocytes rather than during growth or differentiation. The response of pgrn mRNA to ATRA differs in U-937 and HL-60 lineages. In U-937, ATRA and chemical differentiation agents greatly increased pgrn mRNA stability, whereas, in HL-60, ATRA accelerated pgrn mRNA turnover. The initial upregulation of pgrn mRNA after stimulation with ATRA was independent of de novo protein synthesis in U-937 but not HL-60. Chemical blockade of nuclear factor-B (NF-B) activation impaired ATRAstimulated pgrn expression in HL-60 but not U-937, whereas in U-937 it blocked PMA-induced pgrn mRNA expression, suggestive of cellspecific roles for NF-B in determining pgrn mRNA levels. We propose that: 1) ATRA regulates pgrn mRNA levels in myelomonocytic cells; 2) ATRA acts in a cell-specific manner involving the differential control of mRNA stability and differential requirement for NF-B signaling; and 3) elevated pgrn mRNA expression is characteristic of more mature cells and does not stimulate differentiation.granulin; stem cell factor; colony-stimulating factor THE GRANULIN-EPITHELIN precursor progranulin (pgrn; see Ref. 4), which is also called proepithelin (47), PC-cell-derived growth factor (66), or acrogranin (1), is a multifunctional regulatory protein that promotes mitosis, survival, and migration in many cell types (43). It stimulates growth factor-related signaling pathways such as the phosphorylation of shc, p44/42 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, protein kinase B/AKT, and the p70 S6 kinase (24,35,65) and contributes to carcinogenesis in breast (51), ovarian (16,26), renal (18), hepatocellular (10), and prostate (44) cancers, gliomas (33), and multiple myelomas (63). Physiologically, pgrn is involved in wound repair (25,67) and is expressed during development (8) where it regulates cavitation in preimplantation embryos (17), blastocyst hatching (48), and malespecific differentiation of the neonatal hypothalamus (56,58).The granulin (GRN) gene is highly expressed in monocytederived cells, being the 17th and 30th most abundant transcript in human macrophage (9) and monocyte-derived dendritic cells (21), respectively. Peptides derived from pgrn, the granulin/ epit...