The Role of Chaperone-Mediated Autophagy in Bortezomib Resistant Multiple Myeloma

Abstract

Multiple myeloma (MM) remains incurable despite high-dose chemotherapy, autologous stem cell transplants and novel agents. Even with the improved survival of MM patients treated with novel agents, including bortezomib (Bz), the therapeutic options in relapsed/refractory MM remain limited. The majority of MM patients eventually develop resistance to Bz, although the mechanisms of the resistance are poorly understood. Methods: Lysosomal associated membrane protein 2A (LAMP2A) mRNA and protein expression levels were assessed in ex vivo patient samples and a Bz-resistant MM cell line model by in real-rime PCR, western blotting and immunohistochemistry. In vitro modelling of chaperone-mediated autophagy (CMA) activity in response to ER stress were assessed by western blotting and confocal microscopy. The effects of CMA inhibition on MM cell viability and Bz sensitivity in MM cells were assessed by Annexin V/7AAD apoptosis assays using flow cytometry. Results: In this study, there is evidence that CMA, a chaperone-mediated protein degradation pathway, is upregulated in Bz-resistant MM and the inhibition of CMA sensitises resistant cells to Bz. The protein levels of LAMP2A, the rate-limiting factor of the CMA pathway, are significantly increased in MM patients resistant to Bz and within our Bz-resistant cell line model. Bz-resistant cell lines also possessed higher basal CMA activity than the Bz-sensitive parent cell line. In MM cell lines, CMA activity was upregulated in response to ER stress induced by Bz. The inhibition of CMA sensitises Bz-resistant cells to Bz and the combination of CMA inhibition and Bz in vitro had a more cytotoxic effect on myeloma cells than Bz alone. Conclusion: In summary, the upregulation of CMA is a potential mechanism of resistance to Bz and a novel target to overcome Bz-resistant MM.

Looking into Endoplasmic Reticulum Stress: The Key to Drug-Resistance of Multiple Myeloma?

“…Moreover, in MM cells, chaperone-mediated autophagy, a subtype of autophagy that is specific to degradation of cytosolic proteins initiated under ERS, has been demonstrated to confer resistance to BZ [ 103 ]. However, a couple of studies have shown that ERS-mediated autophagy may lead to MM cell death as well.…”

Chaperone-Mediated Autophagy in Neurodegenerative Diseases: Molecular Mechanisms and Pharmacological Opportunities

“…In a bortezomib resistance study, bortezomib confirmed the upregulation capacity in CMA. They found that bortezomib-induced endoplasmic reticulum stress is the main factor of CMA activation by evaluating the LAMP2A protein level [ 109 ]. Although bortezomib treatment benefits MM, the bortezomib-induced peripheral neuropathy (BiPN) in MM patients is a novel issue.…”

Progress in the studies on the molecular mechanisms associated with multidrug resistance in cancers

“…CMA can be reduced by inhibitors of the HSP90 and of glucose-6-phosphate dehydrogenase 161 . A chaperone-mediated protein degradation pathway, is upregulated in bortezomib (Bz)-resistant multiple myeloma (MM) cells, accompanied with increased levels of lysosomal associated membrane protein 2A (LAMP2A), the rate-limiting factor of the CMA pathway; the inhibition of CMA sensitizes resistant cells to Bz 162 . Recent studies showed that HSP70 inhibition in resistant breast cancer cells might enhance autophagy and chemoresistance 163 .…”