Intracellular leucine-rich alpha-2-glycoprotein-1 competes with Apaf-1 for binding cytochrome c in protecting MCF-7 breast cancer cells from apoptosis

AbstractLeucine-rich alpha-2-glycoprotein-1 (LRG1) has been shown to compete with apoptosis activating factor-1 (Apaf-1) for binding cytochromec (Cytc) and could play a role in inhibition of apoptosis. Employing MCF-7 breast cancer cells, we report that intracellular LRG1 does protect against apoptosis. Thus, cells transfected with thelrg1 gene and expressing higher levels of LRG1 were more resistant to hydrogen peroxide-induced apoptosis than parental cells, while cells in which LRG mRNA was knocked down by short hairpin (sh) RNA-induced degradation were more sensitive. The amount of Cytc co-immunoprecipitated with Apaf-1 from the cytosol of apoptotic cells was inversely related to the level of LRG1 expression. Inlrg1-transfected cells partially-glycosylated LRG1 was found in the cytosol and there was an increase in cytosolic Cytc in livelrg1-transfected cells relative to parental cells. However, apoptosis was not spontaneously induced because Cytc was bound to LRG1 and not to Apaf-1. Cytc was the only detectable protein co-immunoprecipitated with LRG1. Following hydrogen peroxide treatment degradation of LRG1 allowed for induction of apoptosis. We propose that intracellular LRG1 raises the threshold of cytoplasmic Cytc required to induce apoptosis and, thus, prevents onset of the intrinsic pathway in cells where Cytc release from mitochondria does not result from committed apoptotic signaling. This mechanism of survival afforded by LRG1 is likely to be distinct from its ext...

Source: Apoptosis - January 1, 2021 Category: Molecular Biology Source Type: research