Unfolded protein response inducers tunicamycin and dithiothreitol promote myeloma cell differentiation mediated by XBP-1

Abstract

The unfolded protein response (UPR) is an essential pathway for both normal and malignant plasma cells to maintain endoplasmic reticulum (ER) homeostasis in response to the large amount of immunoglobulin (Ig) output. The inositol-requiring enzyme 1-X-box binding protein-1 (IRE1-XBP-1) arm of the UPR pathway has been shown to play crucial roles not only in relieving the ER stress by up-regulating a series of genes favoring ER-associated protein degradation and protein folding, but in mediating terminal plasmacytic differentiation and maturation. Myeloma cells comprise various subsets arrested in diverse differentiated phases, and the immaturity of myeloma cells has been taken as a marker for poor prognosis, suggesting that differentiation induction would be a promising therapeutic strategy for myeloma. Herein, we used low-dose pharmacological UPR inducers such as tunicamycin (TM) and dithiothreitol (DTT) to efficiently activate the IRE1-XBP-1 pathway in myeloma cells characterized by transcriptional expression increase in spliced XBP-1 and molecular chaperons, accompanied by significant differentiation and maturation of these myeloma cells, without concomitant cytotoxicity. These differentiated myeloma cells exhibited a more mature appearance with well-developed cytoplasm and a reduced nucleocytoplasmic ratio, and a further differentiated phenotype with markedly increased expression of CD49e together with significantly elevated cellular secretion of Ig light chain as shown by flow cytometry and ELISA, in contrast to the control myeloma cells without exposed to TM or DTT. Moreover, siRNA knockdown of XBP-1 disrupted TM- or DTT-induced myeloma cell differentiation and maturation. Our study, for the first time, validated that the modest activation of the UPR pathway enables myeloma cells to further differentiate, and identified that XBP-1 plays an indispensable role in UPR-mediated myeloma cell differentiation and maturation. Thus, we provided the rationale and feasibility for the exploration of the novel therapeutic strategy of differentiation induction for plasmacytic malignancies.

HIV‐1 Tat‐induced bystander apoptosis in Jurkat cells involves unfolded protein responses

“…Similarly to others UPR markers assayed, our findings demonstrate that Tat stimuli also significantly induces expression of the IRE1‐XBP1 axis, in line with the literature . Interestingly, it has been reported that a viral‐induced IRE1 branch activation is involved in both ER homeostatic restoration and cellular survival, and in the triggering of several apoptosis‐regulating mechanisms . This condition is further evidence that the observed Tat‐induced increase of XBP1 mRNA happens in parallel with the impairment in cell proliferation at 48 hours, indicating the metabolic targeting of homeostasis repair prior to the marked apoptosis induction shown at the later experimental time point.…”

“…6,39 Interestingly, it has been reported that a viral-induced IRE1 branch activation is involved in both ER homeostatic restoration and cellular survival, and in the triggering of several apoptosis-regulating mechanisms. 34,38,42 This condition is further evidence that the observed Tat-induced increase of XBP1 mRNA happens in parallel with the impairment in cell proliferation at It is well documented that, if UPR-mediated efforts to correct protein-folding fails, apoptosis ensues; in this context, several mechanisms have been proposed to account for the generations of apoptotic signals following ER stress. 19,40 The most relevant of these is mediated through the UPR-related CHOP signalling.…”

Deregulation of KSHV latency conformation by ER-stress and caspase-dependent RAD21-cleavage

“…To determine if other agents known to induce ER-stress had similar effects on RAD21 and KSHV transcription, we assayed the reducing agent dithiothreitol (DTT) along with puromycin ( Fig 2A–2C ). DTT is known to induce ER stress in cultured B-lymphocytes [ 38 ]. DTT (5 mM) treatment for 6 hrs resulted in the partial (~50%) cleavage of RAD21 to generate the smaller (60 kDa) form, while puromycin led to a more complete cleavage of RAD21 ( Fig 2A ).…”

Unravel the molecular mechanism of XBP1 in regulating the biology of cancer cells

“…XBP1 is crucial for the differentiation in multiple cell types, including adipocytes, myocytes, and plasma cells. XBP1 is necessary for terminal differentiation of B cells into immunoglobulin-secreting plasma cells 56, 57. XBP1 also coordinates changes in cellular structure and function, as demonstrated by improvement of cell size, lysosome content, mitochondrial mass and function, ribosome number, and total protein synthesis 58.…”