Proteolytic conversion of single chain precursor macrophage-stimulating protein to a biologically active heterodimer

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Highly Efficient Transfection of Human THP-1 Macrophages by Nucleofection
07:54

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Published on: September 2, 2014

M H Wang1, T Yoshimura, A Skeel

  • 1Immunopathology Section, National Cancer Institute, National Institutes of Health, Frederick, Maryland 21702.

The Journal of Biological Chemistry
|February 4, 1994
PubMed

Insights

Human serum macrophage stimulating protein (MSP) circulates as an inactive precursor. Proteolytic cleavage by coagulation factors activates MSP, enabling macrophage stimulation and phagocytic activity.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Immunology

Background:

  • Macrophage stimulating protein (MSP) is a disulfide-linked heterodimer that enhances macrophage motility and phagocytosis.
  • MSP belongs to the kringle protein family, often existing as inactive precursors requiring proteolytic cleavage for activation.

Purpose of the Study:

  • To investigate the proteolytic processing of recombinant pro-MSP and its necessity for biological activity.
  • To determine if enzymes from the intrinsic coagulation cascade can activate pro-MSP.

Main Methods:

  • Recombinant pro-MSP was expressed and labeled with [35S]cysteine in transfected Chinese hamster ovary cells.
  • Proteolytic processing was analyzed in cell culture media with and without serum, and in the presence of protease inhibitors.
  • Activation by specific coagulation proteases (kallikrein, factor XIIa, factor XIa) was assessed.

Main Results:

  • Pro-MSP was secreted as a single chain and processed to the mature heterodimer over hours in serum-containing media.
  • Serine protease inhibitors blocked pro-MSP cleavage, and cleavage did not occur in serum-free conditions.
  • Coagulation proteases kallikrein, factor XIIa, and factor XIa rapidly cleaved pro-MSP into active MSP.
  • Activated MSP exhibited biological activity comparable to natural MSP.

Conclusions:

  • Human serum MSP circulates as a biologically inactive precursor.
  • Enzymes of the intrinsic coagulation cascade can activate pro-MSP, suggesting a mechanism for regulating macrophage activity.

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