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Restricted epithelial proliferation by lacritin via PKCalpha-dependent NFAT and mTOR pathways.

Wang J, Wang N, Xie J, Walton SC, McKown RL, Raab RW, Ma P, Beck SL, Coffman GL, Hussaini IM, Laurie GW - J. Cell Biol. (2006)

Bottom Line: The use of inhibitors or siRNA suggests that lacritin mitogenic signaling involves Galpha(i) or Galpha(o)-PKCalpha-PLC-Ca2+-calcineurin-NFATC1 and Galpha(i) or Galpha(o)-PKCalpha-PLC-phospholipase D (PLD)-mTOR in a bell-shaped, dose-dependent manner requiring the Ca2+ sensor STIM1, but not TRPC1.This pathway suggests the placement of transiently dephosphorylated and perinuclear Golgi-translocated PKCalpha upstream of both Ca2+ mobilization and PLD activation in a complex with PLCgamma2.Outward flow of lacritin from secretory cells through ducts may generate a proliferative/secretory field as a different unit of cellular renewal in nongermative epithelia where luminal structures predominate.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia, Charlottesville, VA 22904, USA.

ABSTRACT
Renewal of nongermative epithelia is poorly understood. The novel mitogen "lacritin" is apically secreted by several nongermative epithelia. We tested 17 different cell types and discovered that lacritin is preferentially mitogenic or prosecretory for those types that normally contact lacritin during its glandular outward flow. Mitogenesis is dependent on lacritin's C-terminal domain, which can form an alpha-helix with a hydrophobic face, as per VEGF's and PTHLP's respective dimerization or receptor-binding domain. Lacritin targets downstream NFATC1 and mTOR. The use of inhibitors or siRNA suggests that lacritin mitogenic signaling involves Galpha(i) or Galpha(o)-PKCalpha-PLC-Ca2+-calcineurin-NFATC1 and Galpha(i) or Galpha(o)-PKCalpha-PLC-phospholipase D (PLD)-mTOR in a bell-shaped, dose-dependent manner requiring the Ca2+ sensor STIM1, but not TRPC1. This pathway suggests the placement of transiently dephosphorylated and perinuclear Golgi-translocated PKCalpha upstream of both Ca2+ mobilization and PLD activation in a complex with PLCgamma2. Outward flow of lacritin from secretory cells through ducts may generate a proliferative/secretory field as a different unit of cellular renewal in nongermative epithelia where luminal structures predominate.

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Proposed model of lacritin mitogenic signaling pathway lacritin signaling suggested by data outlined in the text. Involvement of HPSE (“Hep'ase”) to unblock a lacritin-binding site on SDC1 is from Ma et al. (2006). “?” indicates putative GPCR or ion channel. Dashed lines and items in italics are presumed. PKCα's role upstream of calcineurin (Calcin) is not shown for simplicity.
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fig10: Proposed model of lacritin mitogenic signaling pathway lacritin signaling suggested by data outlined in the text. Involvement of HPSE (“Hep'ase”) to unblock a lacritin-binding site on SDC1 is from Ma et al. (2006). “?” indicates putative GPCR or ion channel. Dashed lines and items in italics are presumed. PKCα's role upstream of calcineurin (Calcin) is not shown for simplicity.

Mentions: Recently, Fang et al. (2003) demonstrated that phosphatidic acid generated by PLD1 activates the rapamycin-sensitive mTOR–pS6K1 pathway. mTOR–pS6K1 regulates mitogenicity and cell growth by promoting protein translation necessary for G1 cell cycle transition (Lane et al., 1993). Preincubation of cells with 100 nM of the mTOR inhibitor rapamycin (Fig. 9 D) or depletion of mTOR (Fig. 9 C) by siRNA was inhibitory. Both also suppressed COX2 expression (Fig. 9 B). Recently phosphoactivated RSK was found to bind and stabilize an activated NFATC4–DNA complex, thereby contributing to transcriptional activation (Yang et al., 2005). Phosphorylation of RSK is rapamycin-insensitive and downstream of p42/p44. In Fig. 1 D, we showed that p42/p44 is not activated by lacritin. In keeping with this result, no evidence of RSK activation could be detected in lacritin-treated cells (unpublished data). Collectively, these data suggest that mitogenic Gαi or Gαo–PKCα-PLC–Ca2+–calcineurin–NFATC1 and Gαi or Gαo–PKCα-PLC–Ca2+–calcineurin–PLD1–mTOR pathways are triggered by lacritin via STIM1 activation (Fig. 10).


Restricted epithelial proliferation by lacritin via PKCalpha-dependent NFAT and mTOR pathways.

Wang J, Wang N, Xie J, Walton SC, McKown RL, Raab RW, Ma P, Beck SL, Coffman GL, Hussaini IM, Laurie GW - J. Cell Biol. (2006)

Proposed model of lacritin mitogenic signaling pathway lacritin signaling suggested by data outlined in the text. Involvement of HPSE (“Hep'ase”) to unblock a lacritin-binding site on SDC1 is from Ma et al. (2006). “?” indicates putative GPCR or ion channel. Dashed lines and items in italics are presumed. PKCα's role upstream of calcineurin (Calcin) is not shown for simplicity.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1761701&req=5

fig10: Proposed model of lacritin mitogenic signaling pathway lacritin signaling suggested by data outlined in the text. Involvement of HPSE (“Hep'ase”) to unblock a lacritin-binding site on SDC1 is from Ma et al. (2006). “?” indicates putative GPCR or ion channel. Dashed lines and items in italics are presumed. PKCα's role upstream of calcineurin (Calcin) is not shown for simplicity.
Mentions: Recently, Fang et al. (2003) demonstrated that phosphatidic acid generated by PLD1 activates the rapamycin-sensitive mTOR–pS6K1 pathway. mTOR–pS6K1 regulates mitogenicity and cell growth by promoting protein translation necessary for G1 cell cycle transition (Lane et al., 1993). Preincubation of cells with 100 nM of the mTOR inhibitor rapamycin (Fig. 9 D) or depletion of mTOR (Fig. 9 C) by siRNA was inhibitory. Both also suppressed COX2 expression (Fig. 9 B). Recently phosphoactivated RSK was found to bind and stabilize an activated NFATC4–DNA complex, thereby contributing to transcriptional activation (Yang et al., 2005). Phosphorylation of RSK is rapamycin-insensitive and downstream of p42/p44. In Fig. 1 D, we showed that p42/p44 is not activated by lacritin. In keeping with this result, no evidence of RSK activation could be detected in lacritin-treated cells (unpublished data). Collectively, these data suggest that mitogenic Gαi or Gαo–PKCα-PLC–Ca2+–calcineurin–NFATC1 and Gαi or Gαo–PKCα-PLC–Ca2+–calcineurin–PLD1–mTOR pathways are triggered by lacritin via STIM1 activation (Fig. 10).

Bottom Line: The use of inhibitors or siRNA suggests that lacritin mitogenic signaling involves Galpha(i) or Galpha(o)-PKCalpha-PLC-Ca2+-calcineurin-NFATC1 and Galpha(i) or Galpha(o)-PKCalpha-PLC-phospholipase D (PLD)-mTOR in a bell-shaped, dose-dependent manner requiring the Ca2+ sensor STIM1, but not TRPC1.This pathway suggests the placement of transiently dephosphorylated and perinuclear Golgi-translocated PKCalpha upstream of both Ca2+ mobilization and PLD activation in a complex with PLCgamma2.Outward flow of lacritin from secretory cells through ducts may generate a proliferative/secretory field as a different unit of cellular renewal in nongermative epithelia where luminal structures predominate.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, University of Virginia, Charlottesville, VA 22904, USA.

ABSTRACT
Renewal of nongermative epithelia is poorly understood. The novel mitogen "lacritin" is apically secreted by several nongermative epithelia. We tested 17 different cell types and discovered that lacritin is preferentially mitogenic or prosecretory for those types that normally contact lacritin during its glandular outward flow. Mitogenesis is dependent on lacritin's C-terminal domain, which can form an alpha-helix with a hydrophobic face, as per VEGF's and PTHLP's respective dimerization or receptor-binding domain. Lacritin targets downstream NFATC1 and mTOR. The use of inhibitors or siRNA suggests that lacritin mitogenic signaling involves Galpha(i) or Galpha(o)-PKCalpha-PLC-Ca2+-calcineurin-NFATC1 and Galpha(i) or Galpha(o)-PKCalpha-PLC-phospholipase D (PLD)-mTOR in a bell-shaped, dose-dependent manner requiring the Ca2+ sensor STIM1, but not TRPC1. This pathway suggests the placement of transiently dephosphorylated and perinuclear Golgi-translocated PKCalpha upstream of both Ca2+ mobilization and PLD activation in a complex with PLCgamma2. Outward flow of lacritin from secretory cells through ducts may generate a proliferative/secretory field as a different unit of cellular renewal in nongermative epithelia where luminal structures predominate.

Show MeSH
Related in: MedlinePlus