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A 17-kd polypeptide, sensitive to bacterial collagenase, is synthesized by bone marrow macrophages
L J Ruland1, P J Quesenberry, G Balian
1Department of Orthopaedics, University of Virginia School of Medicine, Charlottesville 22908.
Abstract:
A novel polypeptide with a molecular weight of 17 kd (17k protein) was identified in bone marrow cell cultures. The synthesis of 17k protein is elevated in cell cultures maintained under Dexter conditions, which support myelopoiesis. The predominance of macrophages in the stromal layer of these cultures and the observation that a mouse myelomonocytic cell line P388D1 is capable of synthesizing large amounts of 17k protein led us to the study of its synthesis by bone marrow macrophages. Metabolic labeling with [14C]proline and partial amino acid analysis of 17k protein demonstrated that the polypeptide contains relatively high amounts of proline and is also sensitive to degradation with bacterial collagenase. However, no hydroxyproline is detectable in 17k protein, and it is extensively degraded with bacterial collagenase. However, no hydroxyproline is detectable in 17k protein, and it is extensively degraded by proteolysis with pepsin, using conditions under which collagen triple helices are resistant to degradation, suggesting that collagen-like structures are not contained in 17k protein. This polypeptide is found predominantly in the cellular layers of bone marrow macrophage cultures. Incorporation of [14C]proline into 17k protein is diminished by increasing concentrations of colony-stimulating factor 1 (CSF-1). The 17k protein may be involved in macrophage proliferation because its synthesis is inhibited by CSF-1, which is required for the maintenance of bone marrow macrophages in vitro.
Insights
A novel 17 kd protein, abundant in bone marrow macrophages, is synthesized during myelopoiesis. Its production is inhibited by colony-stimulating factor 1 (CSF-1), suggesting a role in macrophage proliferation.
Area of Science:
- Biochemistry
- Cell Biology
- Hematology
Background:
- A novel 17 kd polypeptide (17k protein) was identified in bone marrow cell cultures.
- Synthesis of 17k protein is elevated under Dexter conditions supporting myelopoiesis.
- Macrophages predominate in these cultures, and P388D1 cells synthesize large amounts of 17k protein.
Purpose of the Study:
- To investigate the synthesis of 17k protein by bone marrow macrophages.
- To characterize the biochemical properties of 17k protein.
- To determine the regulatory role of colony-stimulating factor 1 (CSF-1) in 17k protein synthesis.
Main Methods:
- Metabolic labeling with [14C]proline.
- Partial amino acid analysis.
- Degradation studies using bacterial collagenase and pepsin.
- Assessment of [14C]proline incorporation in response to varying CSF-1 concentrations.
Main Results:
- 17k protein contains high proline but lacks hydroxyproline, and is sensitive to collagenase and pepsin degradation, indicating it is not collagen-like.
- The polypeptide is primarily located in the cellular layers of bone marrow macrophage cultures.
- CSF-1 diminishes [14C]proline incorporation into 17k protein in a dose-dependent manner.
Conclusions:
- 17k protein is a novel polypeptide synthesized by bone marrow macrophages.
- Its structure is distinct from collagen.
- Inhibition of 17k protein synthesis by CSF-1 suggests a potential role in regulating macrophage proliferation.