Regulation of Macrophage Inflammatory Protein-1alpha Expression by Haemopoietic Growth Factors

Jarmin, David Ian (1998) Regulation of Macrophage Inflammatory Protein-1alpha Expression by Haemopoietic Growth Factors. PhD thesis, University of Glasgow.

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Macrophage inflammatory protein-1 alpha (MIP-1alpha) is a pro-inflammatory cytokine and a regulator of haemopoiesis. Little is currently known regarding the network of regulatory factors controlling the expression of MIP-1alpha, within the bone marrow microenvironment. This study was therefore initiated to further understand how expression of this gene is regulated by haemopoietic growth factors. Macrophages are likely to be an important source of MIP-1alpha within the bone marrow and this study has therefore used primary murine bone marrow-derived macrophages and Northern blot analysis to examine the expression of MIP-1alpha following treatment with various growth factors. The results presented in this thesis show that treatment of bone marrow- derived macrophages with granulocyte-macrophage colony-stimulating factor (GM- CSF) results in a striking increase in MIP-1alpha mRNA levels, relative to control cells. This increase in MIP-1alpha mRNA expression was also followed by an increase in MIP-1alpha protein levels in these cells, suggesting that the potent stimulatory effect of GM- CSF on macrophage-derived MIP-1alpha expression may be of physiological or pathological significance. Since GM-CSF, interleukin- (IL-) 3 and IL-5 all share a common (3-chain subunit in their receptors and can functionally substitute for each other in certain cell types, primary macrophages were also treated with IL-3 or IL-5. A similar increase in mRNA levels was found when macrophages were treated with IL-3, but not IL-5. An increase in the expression of mRNAs for three other CC chemokines: MIP-1alpha, JE and MARC, was also found following treatment with GM- CSF or IL-3, implying that the potent stimulatory effects of GM-CSF and IL-3 are not restricted to MIP-1alpha and may therefore also have an impact on the expression of other CC chemokines. Previous work from our group has provided evidence of an endogenous reciprocal relationship in macrophages, between MIP-1alpha and transforming growth factor-beta (TGF-beta), in which TGF-beta acts to suppress MIP-1alpha expression. To investigate the potential effect of GM-CSF and IL-3 on the relationship between TGF-beta and MIP-1alpha, the effect of TGF-beta on the GM-CSF-or IL-3-induced expression of MIP-1alpha mRNA was assessed. TGF-beta was able to suppress the GM-CSF-or IL-3- induced expression of MIP-1alpha mRNA, but this suppression was not complete. These results suggest that GM-CSF and IL-3 may therefore be two potential stimulatory signals, that may be sufficiently potent to overcome the TGF-beta mediated block on MIP-1alpha expression. Similar effects on the expression of the GM-CSF or IL-3 induced expression of MIP-1alpha, JE and MARC were also observed. The significance of this is unclear, but may reflect the widely recognised function of TGF-beta as an immunosuppressive molecule. A previous study in our laboratory suggested that TGF-beta reversibly downregulated the expression of MIP-1alpha receptors on the murine FDCPmix cell line. Therefore, the effect of GM-CSF and IL-3 on the expression of various receptors for MIP-1alpha on bone marrow-derived macrophages was also examined and an increase in the expression of CCRl mRNA levels was observed, but no change was seen in the level of mRNA for CCR5. This suggests that CCRl and CCR5 expression may be differently regulated in bone marrow-derived macrophages. TGF-beta was observed to have only a minimal suppressive effect on the expression of CCRl and CCR5 mRNA. Binding studies revealed that treatment of bone marrow macrophages with GM-CSF also resulted in an increase in the overall levels of MIP-1alpha receptors on these cells. Scatchard analysis showed that GM-CSF increased the number of MIP-1alpha receptors with no change in the affinity of the remaining receptors for MIP-1alpha ligand. The Kd's for the receptors detected in this study are similar to those previously reported for murine CCRl, but different to those for CCR5. This observation, together with the lack of effect of GM-CSF on CCR5 expression suggests, that this increase in MIP-1alpha receptor numbers probably reflects an increase in the cell surface expression of CCRl. To investigate the functional significance of this increase in MIP-1alpha receptors, the effect of GM-CSF on the ability of macrophages to mobilise calcium in response to MIP-1alpha was examined.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Gerry Graham
Keywords: Immunology
Date of Award: 1998
Depositing User: Enlighten Team
Unique ID: glathesis:1998-75939
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Dec 2019 09:15
Last Modified: 19 Dec 2019 09:15

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