Permissive effect of EGFR-activated pathways on RVI and their anti-apoptotic effect in hypertonicity-exposed mIMCD3 cells

Hypertonicity is a stressful stimulus leading to cell shrinkage and apoptotic cell death. Apoptosis can be prevented if cells are able to activate the mechanism of RVI (regulatory volume increase). This study in mIMCD3 cells presents evidence of a permissive role of the EGFR (epidermal growth factor receptor) on RVI, achieved for the most part through the two main EGFR-triggered signalling chains, the MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) and the PI3K (phosphoinositide 3-kinase)/Akt (also known as protein kinase B) pathways. Hyperosmotic solutions (450 mosM) made by addition of NaCl, increased EGFR phosphorylation, which is prevented by GM6001 and AG1478, blockers respectively, of MMPs (matrix metalloproteinases) and EGFR. Inhibition of EGFR, ERK (PD98059) or PI3K/Akt (wortmannin) phosphorylation reduced RVI by 60, 48 and 58% respectively. The NHE (Na+/H+ exchanger) seems to be the essential mediator of this effect since (i) NHE is the main contributor to RVI, (ii) EGFR, ERK and PI3K/Akt blockers added together with the NHE blocker zoniporide reduce RVI by non-additive effects and (iii) All the blockers significantly lowered the NHE rate in cells challenged by an NH4Cl pulse. Besides reducing RVI, the inhibition of MMP, EGFR and PI3K/Akt had a strong pro-apoptotic effect increasing cell death by 2–3.7-fold. This effect was significantly lower when RVI inhibition did not involve the EGFR-PI3K/Akt pathway. These results provide evidence that Akt and its permissive effect on RVI have a predominant influence on cell survival under hypertonic conditions in IMCD3 cells. This role of Akt operates under the influence of EGFR activation, promoted by MMP.

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Signalling molecules essential for neuronal survival and differentiation

Biochemical Society Transactions ◽

10.1042/bst0341287 ◽

2006 ◽

Vol 34 (6) ◽

pp. 1287-1290 ◽

Cited By ~ 73

Author(s):

K. Frebel ◽

S. Wiese

Keyword(s):

Cell Death ◽

Protein Kinase ◽

Apoptotic Cell ◽

Postnatal Period ◽

Mitogen Activated Protein Kinase ◽

Signalling Molecules ◽

Phosphorylated Akt ◽

Mitogen Activated Protein ◽

Phosphoinositide 3 Kinase ◽

The One

Motoneurons are made in excess throughout development. Initial analysis of the mechanisms that lead to apoptotic cell death during later stages of development and the early postnatal period led to the discovery of neurotrophic factors. These factors comprise different families acting through different tyrosine kinase receptors. Intracellular signalling cascades that lead to the survival of neurons are, on the one hand, the Ras/Raf (Ras-activated factor)/MAPK (mitogen-activated protein kinase) pathway and, on the other, the PI3K (phosphoinositide 3-kinase)/Akt (protein kinase B) pathway. The initial thought of these factors acting as single molecules in separate cascades has been converted into a model in which the dynamics of interaction of these pathways and the subcellular diverse functions of the key regulators have been taken into account. Bag1 (Bcl-2-associated athanogene 1), a molecule that was originally found to act as a co-chaperone of Hsp70 (heat-shock protein 70), also interacts with B-Raf, C-Raf and Akt to phosphorylate Bad (Bcl-2/Bcl-XL-antagonist, causing cell death), a pro-apoptotic member of the Bcl-2 family, and leads to specific subcellular distribution of phosphorylated Akt and B-Raf. These functions lead to survival of embryonic neural stem cells and therefore serve as a key event to regulate the viability of these cells.

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