Role of p38 in regulation of hematopoiesis: effect of p38 inhibition on cytokine production and transcription factor activity in human bone marrow stromal cells.

This study was designed to evaluate effects of specific p38 MAP kinase inhibition on gene and protein expression of essential hematopoietic cytokines in primary human bone marrow stromal cells (HBMSC) and to identify downstream transcription factors (TF) regulated by the p38 MAP kinase signalling pathway. In vitro effects of p38 inhibitors (p38i) on cytokine regulation were compared to inhibitors of other major signalling pathways including PI3 kinase, JNK, MEK-1, NF-kappaB or protein kinase C (PKC). HBMSC were pre-treated with p38i (SB-203580) for 1 h and then stimulated with 200 ng/ml lipopolysaccharide (LPS). Supernatants and RNA were collected 6 h post LPS treatment for quantitative protein and mRNA analyses by ELISA and real-time RT-PCR, respectively, for interleukin-6 (IL-6), interleukin-11 (IL-11), granulocyte-monocyte colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF) and Activin A. Effects of the inhibitors of PI3 kinase (LY294002), JNK (synthetic inhibitory peptide), MEK-1 (PD90859), NF-kappaB (pyrrolidinedithiocarbamate (PDTC)) and protein kinase C (calphostin C) on HBMSC expression hematopoietic cytokines were evaluated and compared. SB-203580 caused dose-dependent decreases in cytokine protein expression and decreased IL-6 and IL-11 mRNA expression. Of the pathway inhibitors examined, only NF-kappaB elicited similar effects on cytokine protein and mRNA expression. p38-regulated transcription factor activity was assessed using a DNA/Protein array. Several TFs linked to cytokine regulation were modulated by SB-203580, with 10 of 21 p38-regulated TFs identified have not been previously linked to downstream p38 signalling. These observations in cultured HBMSC have illustrated the involvement of cytokine proteins, mRNA and TF activities and may improve the current understanding of the in vivo p38i suppression of erythropoiesis. In addition, these results suggest that IL-6, IL-11, GM-CSF, G-CSF and Activin A are similarly regulated by p38 and NF-kappaB and that the MEK1, JNK and PKC pathways appear to play a more limited role in modulating cytokine expression in HBMSC.

Effects of p38 MAP kinase inhibitors on the differentiation and maturation of erythroid progenitors.

In rodents, p38 MAP kinase inhibitors (p38is) induce bone marrow hypocellularity and reduce reticulocyte and erythrocyte counts. To identify target cell populations affected, a differentiating primary liquid erythroid culture system using sca-1(+)cells from mouse bone marrow was developed and challenged with p38is SB-203580, SB-226882, and SB-267030. Drug-related alterations in genes involved at different stages of erythropoiesis, cell-surface antigen expression (CSAE), burst-forming unit erythroid (BFU-E) colony formation, and cellular morphology (CM), growth (CG), and viability were evaluated. CSAE, CM, and decreases in BFU-E formation indicated delayed maturation, while CG and viability were unaffected. Terminal differentiation was delayed until day 14 versus day 7 in controls. CSAE demonstrated higher percentages of sca-1(+)cells after day 2 and reduced percentages of ter119(+) cells after day 7 in all treated cultures. Real-time reverse transcriptase polymerase chain reaction revealed a transient delay in expression of genes involved at early, intermediate, and late stages of erythropoiesis, followed by rebound expression at later time points. Results demonstrate p38is do not irreversibly inhibit erythrogenesis but induce a potency-dependent, transient delay in erythropoietic activity. The delay in activity is suggestive of effects on sca-1(+)bone marrow cells caused by alterations in expression of genes related to erythroid commitment and differentiation resulting in delayed maturation.

In vitro expansion of human cord blood CD36+ erythroid progenitors: temporal changes in gene and protein expression.

OBJECTIVE: Erythropoiesis involves proliferation and differentiation of committed erythroid progenitors to mature red blood cells. The objective of this study was to characterize growth characteristics of human CD36+ erythroid progenitors and to profile temporal expression of lineage-specific transcription factors, structural proteins, and growth factor receptors involved in erythropoiesis. MATERIALS AND METHODS: Erythropoietin-induced differentiation of human cord blood CD36+ erythroid progenitors was profiled for GATA-1, GATA-2, NFE2, EKLF, SCL, PU.1, Id1, Evi-1, c-myb, Hox2.2, c-kit, EpoR, glycophorin A (GPA), CD71, beta- and gamma-globin, and protein 4.2 gene and/or protein expression and DNA content analysis on days 4, 7, and 15 of culture. RESULTS: Real-time RT-PCR analysis revealed upregulation of GATA-1, Id1, glycophorin A, and protein 4.2 mRNA expression on day 7 when compared to day 4 and decreased expression on day 15. EKLF, GATA-2, Hox2.2, c-myb, Evi-1, c-kit, and PU.1 mRNA expression decreased on days 7 and 15. NFE2, CD71, SCL, and EPO-R mRNA expression remained similar on days 4 and 7 but decreased on day 15. Expression of globin genes beta- and gamma-globin increased on both day 7 and day 15 compared to day 4. Values from flow cytometric quantitation of glycophorin A, transferrin receptor (CD71), and hemoglobin A proteins correlated with gene expression results. DNA analysis demonstrated that most cells lacked DNA content by day 15, a finding consistent with enucleation and terminal erythroid differentiation. CONCLUSION: These data indicate that in vitro liquid cultures of committed CD36+ erythroid progenitor cells retain, in part, many features of erythropoiesis at the cellular and molecular level and may provide a useful model for assessment of disease-related or drug-induced erythropoietic abnormalities.

Cloning, expression, and initial characterization of a novel cytokine-like gene family.

We report the identification and characterization of a novel cytokine-like gene family using structure-based methods to search for novel four-helix-bundle cytokines in genomics databases. There are four genes in this family, FAM3A, FAM3B, FAM3C, and FAM3D, each encoding a protein (224-235 amino acids) with a hydrophobic leader sequence. Northern analysis indicates that FAM3B is highly expressed in pancreas, FAM3D in placenta, and FAM3A and FAM3C in almost all tissues. Immunohistochemistry showed that FAM3A is expressed prominently in the vascular endothelium, particularly capillaries. We found that FAM3A and FAM3B protein were both localized to the islets of Langerhans of the endocrine pancreas. Recombinant FAM3B protein has delayed effects on beta-cell function, inhibiting basal insulin secretion from a beta-cell line in a dose-dependent manner.