title: Internalization by multiple endocytic pathways and lysosomal processing impact maspin-based therapeutics.
abstract: Patients with metastatic disease face high rates of mortality with a paucity of therapeutic options. Protein-based therapeutics provide advantages over traditional chemotherapy through increased specificity, decreased immune impairment, and more direct means of delivery. However, development is often hindered because of insufficient knowledge about protein processing by cells when exogenously applied. This study focuses on recombinant Maspin (rMaspin), a serine protease inhibitor (SERPINB5), which alters invasive properties when directly applied to cancer cells. Previous evidence suggests differences in the effects of rMaspin treatment when compared with endogenous reexpression, with little explanation for these discrepancies. A leading hypothesis is that exogenously applied rMaspin is subject to different regulatory and/or processing mechanisms in cancer cells when compared with endogenous expression. Therefore, a more detailed understanding of the mechanisms of internalization and subcellular trafficking of rMaspin is needed to guide future translational development. We describe the molecular trafficking of rMaspin in cytoplasmic vesicles of the endosomal/lysosomal pathway and characterize its uptake by multiple endocytic mechanisms. Time-lapse laser scanning confocal microscopy shows the uptake, in real time, of dye-labeled rMaspin in cancer cells. This study indicates that cellular processing of rMaspin plays a key role by affecting its biologic activity and highlights the need for new approaches aimed at increasing the availability of rMaspin when used to treat cancer.
  
  
  CONCLUSIONS
  Novel characterization of internalization and subcellular trafficking of rMaspin provides new insights for future therapeutic development.
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Bodenstine
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Richard E B
authors.initials: RE
authors.lastname: Seftor
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Elisabeth A
authors.initials: EA
authors.lastname: Seftor
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Zhila
authors.initials: Z
authors.lastname: Khalkhali-Ellis
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Samii
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: J Cesar
authors.initials: JC
authors.lastname: Monarrez
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois.
authors.forename: Grace S
authors.initials: GS
authors.lastname: Chandler
authors.affiliation: SerPlus Technology LLC, Belmont, California.
authors.forename: Philip A
authors.initials: PA
authors.lastname: Pemberton
authors.affiliation: Stanley Manne Children's Research Institute, Cancer Biology and Epigenomics Program, Northwestern University Feinberg School of Medicine, Robert H. Lurie Comprehensive Cancer Center, Chicago, Illinois. m-hendrix@northwestern.edu.
authors.forename: Mary J C
authors.initials: MJ
authors.lastname: Hendrix
mesh_terms: D015415:Biomarkers / Q000378:metabolism; D045744:Cell Line, Tumor; D002966:Clathrin / Q000378:metabolism; D022162:Cytoplasmic Vesicles / Q000187:drug effects / Q000378:metabolism; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D009361:Neoplasm Invasiveness; D021381:Protein Transport / Q000187:drug effects; D034741:RNA, Small Interfering / Q000378:metabolism; D015843:Serpins / Q000494:pharmacology*; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism
chemical_list: D015415:Biomarkers; D002966:Clathrin; D034741:RNA, Small Interfering; C085344:SERPIN-B5; D015843:Serpins