Monolayer versus aggregate balance in survival process for EGF-induced apoptosis in A431 carcinoma cells: Implication of ROS-P38 MAPK-integrin alpha2beta1 pathway.

Abstract

A431 cells escape EGF-induced apoptosis by forming cell aggregates. We show that these clusters migrate and merge with neighboring ones, resulting in larger structures composed of a multilayer central (3D) population surrounded by a cell monolayer (2D). We found that after 48 hr of 10 nM EGF treatment, 3D structure formation correlates with alpha2beta1 integrin upregulation. Blockade of alpha2 integrin impairs 3D structure formation. We studied the involvement of reactive oxygen species (ROS) in this process. We show that A431 cells express the NADPH oxidase catalytic subunits Nox1. EGF-induced dose-dependent ROS production was inhibited by the NADPH oxidase inhibitor, diphenylene iodonium (DPI), in these cells while rotenone was ineffective. Inhibition of ROS level in A431 cells with DPI or ebselen (glutathione peroxydase mimic) as well as P38 MAP kinase inhibition by SB203580 decreases alpha2 integrin subunit expression and induces a shift to 3D versus 2D populations. Cell cycle analysis of 2D cells shows that DPI, ebselen and SB203580 decrease the number of cells in S/G2 phase without affecting the cell number in mitosis phase. On the contrary, for 3D cells, these treatments increased the proportion of cells in mitosis without modification of the cell number in S/G2 phase. For both populations, apoptosis was increased by DPI and ebselen. Resistance of cell aggregates by paclitaxel to cell death is usually described. We show that DPI abolishes paclitaxel resistance of 3D cell aggregates. We observed a greater than additive effect between paclitaxel and DPI resulting in an increased proportion of cells in S/G2 phase for 3D populations. These results suggested that the ROS-P38 MAP kinase-alpha2beta1 integrin pathway was implicated in the A431 survival process by modulating the balance between 2D/3D cells.