Regulation of c-kit expression in human myeloid cells

CSF-1 maintains pathogenic but not homeostatic myeloid cells in the central nervous system during autoimmune neuroinflammation

The receptor for colony stimulating factor 1 (CSF-1R) is important for the survival and function of myeloid cells that mediate pathology during experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). CSF-1 and IL-34, the ligands of CSF-1R, have similar bioactivities but distinct tissue and context-dependent expression patterns, suggesting that they have different roles. This could be the case in EAE, given that CSF-1 expression is up-regulated in the CNS, while IL-34 remains constitutively expressed. We found that targeting CSF-1 with neutralizing antibody halted ongoing EAE, with efficacy superior to CSF-1R inhibitor BLZ945, whereas IL-34 neutralization had no effect, suggesting that pathogenic myeloid cells were maintained by CSF-1. Both anti–CSF-1 and BLZ945 treatment greatly reduced the number of monocyte-derived cells and microglia in the CNS. However, anti–CSF-1 selectively depleted inflammatory microglia and monocytes in inflamed CNS areas, whereas BLZ945 depleted virtually all myeloid cells, including quiescent microglia, throughout the CNS. Anti–CSF-1 treatment reduced the size of demyelinated lesions and microglial activation in the gray matter. Lastly, we found that bone marrow–derived immune cells were the major mediators of CSF-1R–dependent pathology, while microglia played a lesser role. Our findings suggest that targeting CSF-1 could be effective in ameliorating MS pathology, while preserving the homeostatic functions of myeloid cells, thereby minimizing risks associated with ablation of CSF-1R–dependent cells.

Resolution of pluripotential intermediates in murine hematopoietic differentiation by global complementary DNA amplification from single cells: confirmation of assignments by expression profiling of cytokine receptor transcripts

Although hematopoiesis is known to proceed from stem cells through a graded series of multipotent, oligopotent, and unipotent precursor cells, it has been difficult to resolve these cells physically one from another. There is, therefore, corresponding uncertainty about the exact distribution and timing of the expression of genes known to be important in hematopoietic differentiation. In earlier work, the generation of a set of amplified complementary DNAs (cDNAs) from single precursor cells was described, whose biologic potential was determined by the outcome of cultured sibling cells. In this study, the new acquisition of cDNA from multipotent myeloid precursor cells is described, as is the mapping of RNA-level expression of 17 distinct cytokine receptors (c-kit, Flk-1, Flk-2/Flt-3, c-fms, gp130, erythropoietin receptor, GM-CSFRalpha, G-CSFR, TNFR1, IL-1RI, IL-1RII, IL-2Rbeta, IL-3-specific beta receptor, IL-4R, IL-6Ralpha, IL-7Ralpha, and IL-11Ralpha) to the enlarged sample set, spanning stages from pentapotent precursors through oligopotent intermediates to committed and maturing cells in the myeloid and lymphoid lineages. Although the enhanced scope and resolving power of the analysis yielded previously unreported observations, there was overall agreement with known biologic responsiveness at individual stages, and major contradictions did not arise. Moreover, each precursor category displayed a unique overall pattern of hybridization to the matrix of 17 receptor probes, supporting the notion that each sample pool indeed reflected a unique precursor stage. Collectively, the results provide supportive evidence for the validity of the cDNA assignments to particular stages, the depth of the information captured, and the unique capacity of the sample matrix to resolve individual stages in the hematopoietic hierarchy.

Lack of expression of c-KIT in ovarian cancers is associated with poor prognosis

The c-KIT protooncogene encodes a tyrosine kinase receptor, KIT, that is expressed in many normal and cancerous tissues. In this study, we have examined the expression of c-KIT and its ligand, stem cell factor (SCF), in human epithelial ovarian tumors, in normal ovaries and in cultured ovarian surface epithelium (OSE). Cultured cells, normal tissues and tumors were analyzed by Northern and Western blot analyses, reverse transcription-polymerase chain reaction and immunohistochemistry. Normal OSE expressed SCF, but not c-KIT; however, epithelial invaginations and inclusion cysts often expressed KIT protein. Of 15 benign ovarian tumors and tumors of low malignant potential, 87% expressed c-KIT, and 92% of these co-expressed SCF, suggesting the possibility of autocrine growth regulation. Of 35 malignant ovarian cancers, 71% expressed c-KIT (92% co-expressed SCF), with a trend for decreased c-KIT expression in advanced stage disease. Of 34 patients with malignant tumors for whom follow-up information was available (median follow-up time of 24 months), 9 had tumors that did not express c-KIT, 8 (89%) of whom have died and the remaining 1 has recurrent disease. Of the 25 patients with tumors expressing c-KIT, 56% are still alive. Eight of the patients have no evidence of disease and all had KIT-expressing tumors. Statistical analysis indicated that patients whose tumors did not express c-KIT had a significantly shorter (p < 0.05) disease-free survival time than patients who had KIT-expressing tumors. Our results suggest that c-KIT may play a role in early ovarian tumorigenesis, and that loss of c-KIT expression is associated with poor prognosis.

Phenotypic and Functional Changes Induced at the Clonal Level in Hematopoietic Stem Cells After 5-Fluorouracil Treatment

A significant fraction of hematopoietic stem cells (HSCs) have been shown to be resistant to the effects of cytotoxic agents such as 5-fluorouracil (5-FU), which is thought to eliminate many of the rapidly dividing, more committed progenitors in the bone marrow and to provide a relatively enriched population of the most primitive hematopoietic progenitor cells. Although differences between 5-FU–enriched progenitor populations and those from normal bone marrow have been described, it remained unclear if these differences reflected characteristics of the most primitive stem cells that were revealed by 5-FU, or if there were changes in the stem-cell population itself. Here, we have examined some of the properties of the stem cells in the bone marrow before and after 5-FU treatment and have defined several activation-related changes in the stem-cell population. We found that long-term reconstituting stem cells decrease their expression of the growth factor receptor c-kit by 10-fold and increase their expression of the integrin Mac-1 (CD11b). These changes begin as early as 24 hours after 5-FU treatment and are most pronounced within 2 to 3 days. This activated phenotype of HSCs isolated from 5-FU–treated mice is similar to the phenotype of stem cells found in the fetal liver and to the phenotype of transiently repopulating progenitors in normal bone marrow. We found that cell cycle is induced concomitantly with these physical changes, and within 2 days as many as 29% of the stem-cell population is in the S/G2/M phases of the cell cycle. Furthermore, when examined at a clonal level, we found that 5-FU did not appear to eliminate many of the transient, multipotent progenitors from the bone marrow that were found to be copurified with long-term repopulating, activated stem cells. These results demonstrate the sensitivity of the hematopoietic system to changes in its homeostasis and correlate the expression of several important surface molecules with the activation state of HSCs.

Phenotypic and Functional Changes Induced at the Clonal Level in Hematopoietic Stem Cells After 5-Fluorouracil Treatment

A significant fraction of hematopoietic stem cells (HSCs) have been shown to be resistant to the effects of cytotoxic agents such as 5-fluorouracil (5-FU), which is thought to eliminate many of the rapidly dividing, more committed progenitors in the bone marrow and to provide a relatively enriched population of the most primitive hematopoietic progenitor cells. Although differences between 5-FU–enriched progenitor populations and those from normal bone marrow have been described, it remained unclear if these differences reflected characteristics of the most primitive stem cells that were revealed by 5-FU, or if there were changes in the stem-cell population itself. Here, we have examined some of the properties of the stem cells in the bone marrow before and after 5-FU treatment and have defined several activation-related changes in the stem-cell population. We found that long-term reconstituting stem cells decrease their expression of the growth factor receptor c-kit by 10-fold and increase their expression of the integrin Mac-1 (CD11b). These changes begin as early as 24 hours after 5-FU treatment and are most pronounced within 2 to 3 days. This activated phenotype of HSCs isolated from 5-FU–treated mice is similar to the phenotype of stem cells found in the fetal liver and to the phenotype of transiently repopulating progenitors in normal bone marrow. We found that cell cycle is induced concomitantly with these physical changes, and within 2 days as many as 29% of the stem-cell population is in the S/G2/M phases of the cell cycle. Furthermore, when examined at a clonal level, we found that 5-FU did not appear to eliminate many of the transient, multipotent progenitors from the bone marrow that were found to be copurified with long-term repopulating, activated stem cells. These results demonstrate the sensitivity of the hematopoietic system to changes in its homeostasis and correlate the expression of several important surface molecules with the activation state of HSCs.