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The amyloidogenic light chain is a stressor that sensitizes plasma cells to proteasome inhibitor toxicity

Laura Oliva, Ugo Orfanelli, Massimo Resnati, Andrea Raimondi, Andrea Orsi, Enrico Milan, Giovanni Palladini, Paolo Milani, Fulvia Cerruti, Paolo Cascio, Simona Casarini, Paola Rognoni, Thierry Touvier, Magda Marcatti, Fabio Ciceri, Silvia Mangiacavalli, Alessandro Corso, Giampaolo Merlini and Simone Cenci

Key Points

  • Amyloidogenic PCs show unique PI susceptibility and altered organelle homeostasis, consistent with defective autophagy.

  • Amyloidogenic LC production is an intrinsic cellular stressor that sensitizes to PI toxicity.

Publisher's Note: There is an Inside Blood Commentary on this article in this issue.

Abstract

Systemic light chain (AL) amyloidosis is caused by the clonal production of an unstable immunoglobulin light chain (LC), which affects organ function systemically. Although pathogenic LCs have been characterized biochemically, little is known about the biology of amyloidogenic plasma cells (PCs). Intrigued by the unique response rates of AL amyloidosis patients to the first-in-class proteasome inhibitor (PI) bortezomib, we purified and investigated patient-derived AL PCs, in comparison with primary multiple myeloma (MM) PCs, the prototypical PI-responsive cells. Functional, biochemical, and morphological characterization revealed an unprecedented intrinsic sensitivity of AL PCs to PIs, even higher than that of MM PCs, associated with distinctive organellar features and expression patterns indicative of cellular stress. These consisted of expanded endoplasmic reticulum (ER), perinuclear mitochondria, and a higher abundance of stress-related transcripts, and were consistent with reduced autophagic control of organelle homeostasis. To test whether PI sensitivity stems from AL LC production, we engineered PC lines that can be induced to express amyloidogenic and nonamyloidogenic LCs, and found that AL LC expression alters cell growth and proteostasis and confers PI sensitivity. Our study discloses amyloidogenic LC production as an intrinsic PC stressor, and identifies stress-responsive pathways as novel potential therapeutic targets. Moreover, we contribute a cellular disease model to dissect the biology of AL PCs.

  • Submitted August 14, 2016.
  • Accepted January 9, 2017.
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