Maspin Is an Intracellular Serpin That Partitions into Secretory Vesicles and Is Present at the Cell Surface

The tumor suppressor maspin (mammary serpin) was originally identified as a component of human mammary epithelial cells that is downregulated as mammary tumor cells progress from the benign to the invasive and metastatic states. Maspin inhibits cellular invasion, motility, and proliferation, but its mechanism of action is currently unknown. Because the cellular machinery responsible for these processes is cytoplasmic, we have reexamined the tissue distribution and subcellular localization of maspin. We find that maspin, or a maspin-like protein, is present in many human organs, in which it localizes to epithelia. In cultured human mammary myoepithelial cells, maspin is predominantly a soluble cytoplasmic protein that associates with secretory vesicles and is present at the cell surface. In vitro assays show that the vesicle association is due to the existence of an uncleaved facultative secretion signal that allows small amounts of maspin to partition into the endoplasmic reticulum. These results demonstrate that maspin is more widespread than previously believed. The subcellular localization studies indicate that soluble intracellular and vesicle-associated maspin probably play an important role in controlling the invasion, motility, and proliferation of cells expressing it, whereas extracellular maspin may also regulate these processes in adjacent cells.

[1]  H. Kurokawa,et al.  Evaluation of tumor markers in patients with squamous cell carcinoma in the oral cavity. , 1993, International journal of oral and maxillofacial surgery.

[2]  R. Sager,et al.  Production, purification, and characterization of recombinant maspin proteins. , 1994, The Journal of biological chemistry.

[3]  R. Palmiter,et al.  The signal sequence of ovalbumin is located near the NH2 terminus. , 1982, The Journal of biological chemistry.

[4]  J. Demartino,et al.  Polymerase chain reaction facilitates the cloning, CDR-grafting, and rapid expression of a murine monoclonal antibody directed against the CD18 component of leukocyte integrins. , 1991, Nucleic acids research.

[5]  D. Belin,et al.  Plasminogen activator-specific inhibitors produced by human monocytes/macrophages , 1987, The Journal of experimental medicine.

[6]  G von Heijne,et al.  The efficiency of the uncleaved secretion signal in the plasminogen activator inhibitor type 2 protein can be enhanced by point mutations that increase its hydrophobicity. , 1991, The Journal of biological chemistry.

[7]  Eileen Remold-O'Donnell,et al.  The ovalbumin family of serpin proteins , 1993, FEBS letters.

[8]  G. Blobel,et al.  Chicken ovalbumin contains an internal signal sequence , 1979, Nature.

[9]  J. Sambrook,et al.  Molecular Cloning: A Laboratory Manual , 2001 .

[10]  T. Ny,et al.  Intracellular Polymerization of the Serpin Plasminogen Activator Inhibitor Type 2 (*) , 1996, The Journal of Biological Chemistry.

[11]  G. Silverman,et al.  A serine proteinase inhibitor locus at 18q21.3 contains a tandem duplication of the human squamous cell carcinoma antigen gene. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[12]  D. Wong,et al.  Functional implications of the modeled structure of maspin. , 1996, Protein engineering.

[13]  M. Hendrix,et al.  Maspin, a serpin with tumor-suppressing activity in human mammary epithelial cells. , 1994, Science.

[14]  D. Wong,et al.  The Tumor Suppressor Maspin Does Not Undergo the Stressed to Relaxed Transition or Inhibit Trypsin-like Serine Proteases. , 1995, The Journal of Biological Chemistry.

[15]  A. Anisowicz,et al.  Functional diversity of gro gene expression in human fibroblasts and mammary epithelial cells. , 1988, Proceedings of the National Academy of Sciences of the United States of America.

[16]  A. C. Webb,et al.  Human monocyte Arg-Serpin cDNA. Sequence, chromosomal assignment, and homology to plasminogen activator-inhibitor , 1987, The Journal of experimental medicine.

[17]  J. Whisstock,et al.  Function of maspin. , 1994, Science.

[18]  M. Hendrix,et al.  RNA genetics of breast cancer: maspin as paradigm. , 1994, Cold Spring Harbor symposia on quantitative biology.

[19]  John Calvin Reed,et al.  Investigation of the subcellular distribution of the bcl-2 oncoprotein: residence in the nuclear envelope, endoplasmic reticulum, and outer mitochondrial membranes. , 1993, Cancer research.

[20]  M. Hendrix,et al.  Maspin. A tumor suppressing serpin. , 1997, Advances in experimental medicine and biology.

[21]  F. Masiarz,et al.  Characterization of recombinant human insulin-like growth factor binding proteins 4, 5, and 6 produced in yeast. , 1992, The Journal of biological chemistry.

[22]  D. Belin,et al.  Facultative polypeptide translocation allows a single mRNA to encode the secreted and cytosolic forms of plasminogen activators inhibitor 2. , 1989, The EMBO journal.

[23]  D. Arber,et al.  Vimentin-Negative Epithelioid Sarcoma: The Value of an Immunohistochemical Panel That Includes CD34 , 1993, The American journal of surgical pathology.

[24]  R. Ye,et al.  Mammalian protein secretion without signal peptide removal. Biosynthesis of plasminogen activator inhibitor-2 in U-937 cells. , 1988, The Journal of biological chemistry.

[25]  J. Potempa,et al.  The serpin superfamily of proteinase inhibitors: structure, function, and regulation. , 1994, The Journal of biological chemistry.