The STAT3 inhibitor stattic overcome bortezomib-resistance in multiple myeloma via decreasing PSMB6.

Bortezomib, an FDA approved drug in 2003 for newly diagnosed and relapsed/refractory MM, had showed great efficacy in different clinical settings. However, many patients still developed resistance to Bortezomib, and the mechanism of action remains unelucidated. Here, we showed that Bortezomib resistance can be partially overcome by targeting a different subunit of 20 S complex - PSMB6. PSMB6 knock down by shRNA increased sensitivity to Bortezomib in resistant and sensitive cell line. Interestingly, a STAT3 inhibitor, Stattic, is shown to selectively inhibit PSMB6 and induce apoptosis in Bortezomib resistant and sensitive MM cells, even with IL-6 induction. Therefore, PSMB6 is a novel target for Bortezomib resistance and Stattic may offer a potential therapeutic strategy.

A lowered 26S proteasome activity correlates with mantle lymphoma cell lines resistance to genotoxic stress.

BACKGROUND: Mantle cell lymphoma (MCL) is a B-cell hemopathy characterized by the t(11;14) translocation and the aberrant overexpression of cyclin D1. This results in an unrestrained cell proliferation. Other genetic alterations are common in MCL cells such as SOX11 expression, mutations of ATM and/or TP53 genes, activation of the NF-κB signaling pathway and NOTCH receptors. These alterations lead to the deregulation of the apoptotic machinery and resistance to drugs. We observed that among a panel of MCL cell lines, REC1 cells were resistant towards genotoxic stress. We studied the molecular basis of this resistance. METHODS: We analyzed the cell response regarding apoptosis, senescence, cell cycle arrest, DNA damage response and finally the 26S proteasome activity following a genotoxic treatment that causes double strand DNA breaks. RESULTS: MCL cell lines displayed various sensitivity/resistance towards genotoxic stress and, in particular, REC1 cells did not enter apoptosis or senescence after an etoposide treatment. Moreover, the G2/M cell cycle checkpoint was deficient in REC1 cells. We observed that three main actors of apoptosis, senescence and cell cycle regulation (cyclin D1, MCL1 and CDC25A) failed to be degraded by the proteasome machinery in REC1 cells. We ruled out a default of the ßTrCP E3-ubiquitine ligase but detected a lowered 26S proteasome activity in REC1 cells compared to other cell lines. CONCLUSION: The resistance of MCL cells to genotoxic stress correlates with a low 26S proteasome activity. This could represent a relevant biomarker for a subtype of MCL patients with a poor response to therapies and a high risk of relapse.

Selection of suitable reference genes for normalization of genes of interest in canine soft tissue sarcomas using quantitative real-time polymerase chain reaction.

Quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) is a sensitive technique for quantifying gene expression. Stably expressed reference genes are necessary for normalization of RT-qPCR data. Only a few articles have been published on reference genes in canine tumours. The objective of this study was to demonstrate how to identify suitable reference genes for normalization of genes of interest in canine soft tissue sarcomas using RT-qPCR. Primer pairs for 17 potential reference genes were designed and tested in archival tumour biopsies from six dogs. The geNorm algorithm was used to analyse the most suitable reference genes. Eight potential reference genes were excluded from this final analysis because of their dissociation curves. ß-Glucuronidase (GUSB) and proteasome subunit, beta type, 6 (PSMB6) were most stably expressed with an M value of 0.154 and a CV of 0.053 describing their average stability. We suggest that choice of reference genes should be based on specific testing in every new experimental set-up.