Expression and release of glucose-regulated protein-78 (GRP78) in multiple myeloma

Normann Steiner,Bojana Borjan,Eberhard Gunsilius,Georg Göbel,Roman Hajek,Gerold Untergasser,Johann Kern,Wolfgang Willenbacher,Karin Jöhrer

doi:10.18632/oncotarget.17353

Abstract

IntroductionMultiple myeloma (MM) is a plasma cell neoplasm that is mostly incurable due to acquired resistance during the treatment course. Thus, we evaluated expression and release of glucose-regulated protein 78 kDa (GRP78/BiP), an endoplasmic reticulum (ER) based pro-survival chaperone involved in immunoglobulin folding and unfolded protein responses.ResultsGRP78 protein expression in the ER and on the cell surface did not significantly differ between MGUS, NDMM and RRMM patients although there was a trend to higher surface expression in RRMM. In bone marrow plasma, the amount of released GRP78 protein was not significantly increased between MGUS-, NDMM- and RRMM patients. MM cells of the three cell lines release GRP78 as full-length protein under apoptotic, but not under acidotic or ER-stress conditions. In necrosis, only proteolytic fragments of GRP78 were detected in supernatants of MM cells.Materials and MethodsGRP78 protein expression and plasma levels were quantified in bone marrow aspirates of patients with monoclonal gammopathy of undetermined significance (MGUS, n = 29), newly diagnosed MM (NDMM, n = 29) and with relapsed/refractory MM (RRMM, n = 15) by immunohistochemistry and sandwich ELISA. The human MM cell lines U266, NCI-H929 and OPM-2 were used for functional GRP78 release- and processing studies after induction of acidosis, ER stress, apoptosis and necrosis.ConclusionsEctopic expression of GRP78 on cell membrane or its release in the microenvironment is not a suitable marker to distinguish MGUS from NDMM and RRMM.

Highlights

Multiple myeloma (MM) is a plasma cell neoplasm that is mostly incurable due to acquired resistance during the treatment course
Glucose-regulated protein 78 kDa (GRP78) protein expression in the endoplasmic reticulum (ER) and on the cell surface did not significantly differ between MGUS, newly diagnosed MM (NDMM) and RRMM patients there was a trend to higher surface expression in RRMM
GRP78 expression has never been explored as a predictive biomarker in multiple myeloma, an ectopic expression of GRP78 on the cell membrane has been reported in a subgroup of MM patients [14]

Summary

Introduction

Multiple myeloma (MM) is a plasma cell neoplasm that is mostly incurable due to acquired resistance during the treatment course. We evaluated expression and release of glucose-regulated protein 78 kDa (GRP78/BiP), an endoplasmic reticulum (ER) based pro-survival chaperone involved in immunoglobulin folding and unfolded protein responses. GRP78 has been described in different intracellular compartments of malignant cells, e.g. in the ER or the mitochondria, and even on the cell surface [6]. This key chaperone protein of the unfolded protein response (UPR) has been shown by us to be responsible for resistance to the anti-angiogenic activity of the proteasome-inhibitor bortezomib and, by other groups, to BRAF-inhibitors [6,7,8,9,10]. A human immunoglobulin-M antibody (PATSM6) has been described to recognize GRP78 on cell membrane and to induce apoptosis in MM cells [14]

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