Limits...
Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation.

Gilbert S, Loranger A, Daigle N, Marceau N - J. Cell Biol. (2001)

Bottom Line: In these cells, the loss of one partner via a targeted mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins.Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8- versus WT hepatocytes.Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface.

View Article: PubMed Central - PubMed

Affiliation: Centre de recherche en cancérologie et Département de médecine, Université Laval, Québec, G1K 7P4, Canada.

ABSTRACT
Keratins 8 and 18 belong to the keratin family of intermediate filament (IF) proteins and constitute a hallmark for all simple epithelia, including the liver. Hepatocyte IFs are made solely of keratins 8 and 18 (K8/K18). In these cells, the loss of one partner via a targeted mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins. Here, we report that K8- mouse hepatocytes in primary culture and in vivo are three- to fourfold more sensitive than wild-type (WT) mouse hepatocytes to Fas-mediated apoptosis after stimulation with Jo2, an agonistic antibody of Fas ligand. This increased sensitivity is associated with a higher and more rapid caspase-3 activation and DNA fragmentation. In contrast, no difference in apoptosis is observed between cultured K8- and WT hepatocytes after addition of the Fas-related death-factors tumor necrosis factor (TNF) alpha or TNF-related apoptosis-inducing ligand. Analyses of the Fas distribution in K8- and WT hepatocytes in culture and in situ demonstrate a more prominent targeting of the receptor to the surface membrane of K8- hepatocytes. Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8- versus WT hepatocytes. Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface.

Show MeSH

Related in: MedlinePlus

The EGF-signaling pathway is not involved in the protection by K8/K18 against Fas-mediated apoptosis. (A) At a dose of 20 or 200 ng/dish, EGF activation of ERK and Akt, as determined by the phosphorylation level of Thr 202/Tyr 204 (ERK) and Ser 473 (Akt), occurs essentially to identical levels in both WT and K8- hepatocytes. (B) Increasing the EGF concentration to 200 ng/dish decreased the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2196458&req=5

fig3: The EGF-signaling pathway is not involved in the protection by K8/K18 against Fas-mediated apoptosis. (A) At a dose of 20 or 200 ng/dish, EGF activation of ERK and Akt, as determined by the phosphorylation level of Thr 202/Tyr 204 (ERK) and Ser 473 (Akt), occurs essentially to identical levels in both WT and K8- hepatocytes. (B) Increasing the EGF concentration to 200 ng/dish decreased the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes.

Mentions: Cells can be protected from Fas-mediated apoptosis via the activation of survival pathways by growth factors like EGF (Gibson et al., 1999). Considering the major role of EGF in hepatocyte growth regulation, we asked whether it is also involved in the protective resistance provided by K8/K18 in these cells. Notably, the growth-promoting activity occurs via the activation of the ERK-signaling pathway, whereas the protective effect takes place through the activation of the Akt-signaling pathway (Gibson et al., 1999; Roberts et al., 2000). With regard to growth-promoting activity of EGF, we found that, although the ERK pathway was already primed in K8- hepatocytes and little in WT hepatocytes, the addition of EGF led to essentially equivalent increases in ERK activation in both cell populations (Fig. 3 A). Comparable increases in Akt phosphorylation levels were observed in K8- and WT hepatocytes after the addition of either 20 or 200 ng/dish EGF (Fig. 3 A), indicating that the loss of K8/K18 does not affect this EGF protection against Fas-mediated apoptosis. In line with these data on EGF-induced Akt activation, increasing the EGF concentration to 200 ng/dish was sufficient to decrease the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes (Fig. 3 B).


Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation.

Gilbert S, Loranger A, Daigle N, Marceau N - J. Cell Biol. (2001)

The EGF-signaling pathway is not involved in the protection by K8/K18 against Fas-mediated apoptosis. (A) At a dose of 20 or 200 ng/dish, EGF activation of ERK and Akt, as determined by the phosphorylation level of Thr 202/Tyr 204 (ERK) and Ser 473 (Akt), occurs essentially to identical levels in both WT and K8- hepatocytes. (B) Increasing the EGF concentration to 200 ng/dish decreased the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2196458&req=5

fig3: The EGF-signaling pathway is not involved in the protection by K8/K18 against Fas-mediated apoptosis. (A) At a dose of 20 or 200 ng/dish, EGF activation of ERK and Akt, as determined by the phosphorylation level of Thr 202/Tyr 204 (ERK) and Ser 473 (Akt), occurs essentially to identical levels in both WT and K8- hepatocytes. (B) Increasing the EGF concentration to 200 ng/dish decreased the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes.
Mentions: Cells can be protected from Fas-mediated apoptosis via the activation of survival pathways by growth factors like EGF (Gibson et al., 1999). Considering the major role of EGF in hepatocyte growth regulation, we asked whether it is also involved in the protective resistance provided by K8/K18 in these cells. Notably, the growth-promoting activity occurs via the activation of the ERK-signaling pathway, whereas the protective effect takes place through the activation of the Akt-signaling pathway (Gibson et al., 1999; Roberts et al., 2000). With regard to growth-promoting activity of EGF, we found that, although the ERK pathway was already primed in K8- hepatocytes and little in WT hepatocytes, the addition of EGF led to essentially equivalent increases in ERK activation in both cell populations (Fig. 3 A). Comparable increases in Akt phosphorylation levels were observed in K8- and WT hepatocytes after the addition of either 20 or 200 ng/dish EGF (Fig. 3 A), indicating that the loss of K8/K18 does not affect this EGF protection against Fas-mediated apoptosis. In line with these data on EGF-induced Akt activation, increasing the EGF concentration to 200 ng/dish was sufficient to decrease the Fas-induced apoptosis of K8- hepatocytes to a level comparable to that of WT hepatocytes (Fig. 3 B).

Bottom Line: In these cells, the loss of one partner via a targeted mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins.Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8- versus WT hepatocytes.Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface.

View Article: PubMed Central - PubMed

Affiliation: Centre de recherche en cancérologie et Département de médecine, Université Laval, Québec, G1K 7P4, Canada.

ABSTRACT
Keratins 8 and 18 belong to the keratin family of intermediate filament (IF) proteins and constitute a hallmark for all simple epithelia, including the liver. Hepatocyte IFs are made solely of keratins 8 and 18 (K8/K18). In these cells, the loss of one partner via a targeted mutation in the germline results in hepatocytes lacking K8/K18 IFs, thus providing a model of choice for examining the function(s) of simple epithelium keratins. Here, we report that K8- mouse hepatocytes in primary culture and in vivo are three- to fourfold more sensitive than wild-type (WT) mouse hepatocytes to Fas-mediated apoptosis after stimulation with Jo2, an agonistic antibody of Fas ligand. This increased sensitivity is associated with a higher and more rapid caspase-3 activation and DNA fragmentation. In contrast, no difference in apoptosis is observed between cultured K8- and WT hepatocytes after addition of the Fas-related death-factors tumor necrosis factor (TNF) alpha or TNF-related apoptosis-inducing ligand. Analyses of the Fas distribution in K8- and WT hepatocytes in culture and in situ demonstrate a more prominent targeting of the receptor to the surface membrane of K8- hepatocytes. Moreover, altering Fas trafficking by disrupting microtubules with colchicine reduces by twofold the protection generated against Jo2-induced lethal action in K8- versus WT hepatocytes. Together, the results strongly suggest that simple epithelium K8/K18 provide resistance to Fas-mediated apoptosis and that this protection occurs through a modulation of Fas targeting to the cell surface.

Show MeSH
Related in: MedlinePlus