Overexpression of GRP78/BiP in P-Glycoprotein-Positive L1210 Cells is Responsible for Altered Response of Cells to Tunicamycin as a Stressor of the Endoplasmic Reticulum.

Mário Šereš,Boris Lakatoš,Zdena Sulová,Viera Boháčová,Albert Breier,Lucia Pavlíková,Tomáš Kyca,Ivana Borovská

doi:10.3390/cells9040890

Mário Šereš, Boris Lakatoš + Show 6 more

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https://doi.org/10.3390/cells9040890

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Abstract

P-glycoprotein (P-gp, ABCB1 member of the ABC (ATP-binding cassette) transporter family) localized in leukemia cell plasma membranes is known to reduce cell sensitivity to a large but well-defined group of chemicals known as P-gp substrates. However, we found previously that P-gp-positive sublines of L1210 murine leukemia cells (R and T) but not parental P-gp-negative parental cells (S) are resistant to the endoplasmic reticulum (ER) stressor tunicamycin (an N-glycosylation inhibitor). Here, we elucidated the mechanism of tunicamycin resistance in P-gp-positive cells. We found that tunicamycin at a sublethal concentration of 0.1 µM induced retention of the cells in the G1 phase of the cell cycle only in the P-gp negative variant of L1210 cells. P-gp-positive L1210 cell variants had higher expression of the ER stress chaperone GRP78/BiP compared to that of P-gp-negative cells, in which tunicamycin induced larger upregulation of CHOP (C/EBP homologous protein). Transfection of the sensitive P-gp-negative cells with plasmids containing GRP78/BiP antagonized tunicamycin-induced CHOP expression and reduced tunicamycin-induced arrest of cells in the G1 phase of the cell cycle. Taken together, these data suggest that the resistance of P-gp-positive cells to tunicamycin is due to increased levels of GRP78/BiP, which is overexpressed in both resistant variants of L1210 cells.

Highlights

The endoplasmic reticulum (ER) is a multifunctional membrane organelle with a complex interconnected structure that is involved in intracellular signal transduction [1] and protein synthesis, folding, modification, and quality control [2]
Antagonized tunicamycin-induced CHOP expression and reduced tunicamycin-induced arrest of cells in the G1 phase of the cell cycle. These data suggest that the resistance of P-gp-positive cells to tunicamycin is due to increased levels of GRP78/BiP, which is overexpressed in both resistant variants of L1210 cells
Homeostasis, such as calcium storage/release equilibrium or equilibrium in pro-/antioxidant status. This homeostasis depends on the energy abundance/deprivation state of the cells and reflects metabolic stimulation, alterations in glycosylation, activation of inflammatory processes, and increases in protein synthesis. Misbalance in this complicated system leads to an increase in misfolded proteins in the cell [3], which is responsible for the development of ER stress in response to the accumulation of

Summary

Introduction

The endoplasmic reticulum (ER) is a multifunctional membrane organelle with a complex interconnected structure that is involved in intracellular signal transduction [1] and protein synthesis, folding, modification, and quality control [2]. The processes of protein folding and maturation in the ER are controlled by accurate and strictly regulated mechanisms that depend on differential ER homeostasis, such as calcium storage/release equilibrium or equilibrium in pro-/antioxidant status. This homeostasis depends on the energy abundance/deprivation state of the cells and reflects metabolic stimulation, alterations in glycosylation, activation of inflammatory processes, and increases in protein synthesis. The UPR is a pro-survival mechanism that causes a reduction in the accumulation of unfolded proteins through depression of proteosynthesis and acceleration of proteosomal degradation [5].

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