title: Polarized secretion of leukemia inhibitory factor.
abstract: BACKGROUND
  The direction of cytokine secretion from polarized cells determines the cytokine's cellular targets. Leukemia inhibitory factor (LIF) belongs to the interleukin-6 (IL-6) family of cytokines and signals through LIFR/gp130. Three factors which may regulate the direction of LIF secretion were studied: the site of stimulation, signal peptides, and expression levels. Stimulation with IL-1beta is known to promote IL-6 secretion from the stimulated membrane (apical or basolateral) in the human intestinal epithelial cell line Caco-2. Since LIF is related to IL-6, LIF secretion was also tested in Caco-2 following IL-1beta stimulation. Signal peptides may influence the trafficking of LIF. Two isoforms of murine LIF, LIF-M and LIF-D, encode different signal peptides which have been associated with different locations of the mature protein in fibroblasts. To determine the effect of the signal peptides on LIF secretion, secretion levels were compared in Madin-Darby canine kidney (MDCK) clones which expressed murine LIF-M or LIF-D or human LIF under the control of an inducible promoter. Low and high levels of LIF expression were also compared since saturation of the apical or basolateral route would reveal specific transporters for LIF.
  
  
  RESULTS
  When Caco-2 was grown on permeable supports, LIF was secreted constitutively with around 40% secreted into the apical chamber. Stimulation with IL-1beta increased LIF production. After treating the apical surface with IL-1beta, the percentage secreted apically remained similar to the untreated, whereas, when the cells were stimulated at the basolateral surface only 20% was secreted apically. In MDCK cells, an endogenous LIF-like protein was detected entirely in the apical compartment. The two mLIF isoforms showed no difference in their secretion patterns in MDCK. Interestingly, about 70% of murine and human LIF was secreted apically from MDCK over a 400-fold range of expression levels within clones and a 200,000-fold range across clones.
  
  
  CONCLUSIONS
  The site of stimulation affected the polarity of LIF secretion, while, signal peptides and expression levels did not. Exogenous LIF is transported in MDCK without readily saturated steps.
authors.affiliation: School of Life and Health Sciences, Aston University, Birmingham, UK. e.j.hill@aston.ac.uk
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Hill
authors.forename: Ann B
authors.initials: AB
authors.lastname: Vernallis
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D053605:Leukemia Inhibitory Factor / Q000378:metabolism*
chemical_list: D053583:Interleukin-1beta; D015850:Interleukin-6; D053605:Leukemia Inhibitory Factor
references.citation: Curr Biol. 2006 Feb 21;16(4):408-14
references.pmid: 16488876
references.citation: Shock. 2000 May;13(5):374-8
references.pmid: 10807012
references.citation: J Am Coll Surg. 2006 Sep;203(3):353-64
references.pmid: 16931308
references.citation: Protein Expr Purif. 2006 Nov;50(1):102-10
references.pmid: 16893658
references.citation: Annu Rev Biochem. 2007;76:629-45
references.pmid: 17263661
references.citation: Mol Cell Biochem. 2008 Mar;310(1-2):67-75
references.pmid: 18049865
references.citation: J Biol Chem. 2008 Jun 27;283(26):18040-7
references.pmid: 18434305
references.citation: Gut. 1994 Mar;35(3):338-42
references.pmid: 8150343
references.citation: Cytokine. 2000 Mar;12(3):265-71
references.pmid: 10704254
references.citation: Proc Natl Acad Sci U S A. 2000 Mar 28;97(7):3248-53
references.pmid: 10725401
references.citation: Exp Cell Res. 2000 Jul 10;258(1):195-203
references.pmid: 10912801
references.citation: J Immunol. 2000 Oct 15;165(8):4561-6
references.pmid: 11035097
references.citation: J Gastroenterol Hepatol. 2001 Sep;16(9):991-1000
references.pmid: 11595063
references.citation: Traffic. 2002 Apr;3(4):279-88
references.pmid: 11929609
references.citation: J Am Soc Nephrol. 2003 Dec;14(12):3090-101
references.pmid: 14638908
references.citation: J Cell Sci. 2004 Apr 15;117(Pt 10):2063-75
references.pmid: 15054106
references.citation: J Immunol Methods. 1983 Dec 16;65(1-2):55-63
references.pmid: 6606682
references.citation: Proc Natl Acad Sci U S A. 1986 Apr;83(7):2100-4
references.pmid: 3083413
references.citation: Am J Physiol. 1987 Sep;253(3 Pt 1):C433-43
references.pmid: 3307450
references.citation: Cell. 1990 Sep 21;62(6):1105-14
references.pmid: 2119255
references.citation: J Cell Biol. 1993 Aug;122(3):713-9
references.pmid: 8335694
references.citation: Dev Genet. 1993;14(3):165-73
references.pmid: 7689430
references.citation: Cell. 1994 Jul 1;77(7):1101-16
references.pmid: 8020098
references.citation: Exp Cell Res. 1994 Aug;213(2):449-57
references.pmid: 8050502
references.citation: Nature. 1995 Nov 2;378(6552):96-8
references.pmid: 7477300
references.citation: J Cell Biol. 1996 May;133(3):543-58
references.pmid: 8636230
references.citation: Immunol Invest. 1996 Jul;25(4):333-40
references.pmid: 8805054
references.citation: Br J Pharmacol. 1997 Mar;120(5):883-91
references.pmid: 9138695
references.citation: Endocrinology. 1997 Jul;138(7):2863-70
references.pmid: 9202229
references.citation: Eur Cytokine Netw. 1998 Dec;9(4):607-12
references.pmid: 9889404
references.citation: Biochem Biophys Res Commun. 1999 Jan 8;254(1):5-9
references.pmid: 9920723
references.citation: J Endocrinol. 1999 Feb;160(2):181-90
references.pmid: 9924186
references.citation: J Immunol. 1999 Apr 15;162(8):4637-46
references.pmid: 10202003
references.citation: Exp Cell Res. 1999 Jun 15;249(2):199-211
references.pmid: 10366419
references.citation: J Cell Sci. 2004 Dec 1;117(Pt 25):5955-64
references.pmid: 15564373
references.citation: Biochim Biophys Acta. 2005 Jul 10;1744(3):455-64
references.pmid: 15927284
references.citation: J Cell Sci. 2006 May 1;119(Pt 9):1833-42
references.pmid: 16608874