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Differential processing of colony-stimulating factor 1 precursors encoded by two human cDNAs
1Department of Tumor Cell Biology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
Molecular and Cellular Biology
|November 1, 1988
Summary
Investigating macrophage colony-stimulating factor 1 (CSF-1) biosynthesis, this study found that a larger human CSF-1 cDNA clone yields a secreted growth factor. This protein undergoes distinct post-translational modifications compared to a smaller clone, suggesting varied physiological roles.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Macrophage colony-stimulating factor 1 (CSF-1) is a crucial growth factor for myeloid cells.
- Previous studies examined CSF-1 biosynthesis using a 1.6-kb human cDNA clone encoding a 256-amino-acid precursor.
- The role of different CSF-1 precursor lengths in biosynthesis and processing remains to be fully elucidated.
Purpose of the Study:
- To investigate the biosynthesis of CSF-1 using a 4-kb human cDNA clone encoding a 554-amino-acid product.
- To compare the post-translational processing and cellular localization of CSF-1 derived from the 4-kb clone versus the previously studied 1.6-kb clone.
- To explore the potential impact of observed processing differences on CSF-1 function.
Main Methods:
- Transfection of mouse NIH-3T3 fibroblasts with retroviral vectors expressing human CSF-1 cDNA (4-kb and 1.6-kb clones).
- Co-transfection with human c-fms (CSF-1 receptor) cDNA to assess autocrine transformation.
- Analysis of protein synthesis, processing (proteolytic cleavage, glycosylation), and cellular localization using biochemical and enzymatic digestion techniques.
Main Results:
- NIH-3T3 cells expressing the 4-kb CSF-1 clone produced biologically active CSF-1 and underwent autocrine transformation.
- The 4-kb CSF-1 product was synthesized as a transmembrane glycoprotein, rapidly cleaved to a soluble form, and efficiently secreted.
- In contrast, the 1.6-kb CSF-1 precursor was stably membrane-bound with slow cleavage, and the soluble forms differed in glycosylation and polypeptide length, indicating distinct post-translational modifications.
Conclusions:
- The 4-kb human CSF-1 cDNA encodes a precursor efficiently processed to a secreted growth factor with both N-linked and O-linked carbohydrate chains.
- Differences in post-translational processing between the 4-kb and 1.6-kb CSF-1 precursors suggest distinct biological roles in vivo.
- The study highlights the importance of precursor length and processing in determining the functional characteristics of CSF-1.