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-1 beta 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-1 beta
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-1 beta increased LIF production. After treating the
apical surface with IL-1 beta, 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.
Conclusion: 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.
| Original language | English |
|---|---|
| Article number | 53 |
| Number of pages | 10 |
| Journal | BMC Cell Biology |
| Volume | 9 |
| Issue number | 53 |
| DOIs | |
| Publication status | Published - 18 Sept 2008 |
Bibliographical note
© 2008 Hill and Vernallis; licensee BioMed Central Ltd.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.