c-Myc/NOXA pathway participates in ixazomib induced
proliferation inhibition in ESCC cells.
Based on these previous studies, the proteasome inhibitors increased the
accumulation of polyubiquitinated proteins and trigger the endoplasmic
reticulum stress-induce apoptosis in several cancer
cells(Fribley et al. , 2004;
Mozos et al. , 2011;
Niewerth et al. , 2015). To assess
the role of the ixazomib in apoptosis by endoplasmic reticulum stress in
ESCC cells, we determined by RT-PCR the expression levels of endoplasmic
reticulum stress related genes in Kyse150 cell treated with ixazomib.
Results of these experiments showed significant increase in the mRNA
expression levels of endoplasmic reticulum stress related genes in
response to ixazomib. The increased in NOXA expression was the most
prominent compared with other ERS related gene (Figure 4A). As NOXA has
been demonstrated to play a role in ixazomib-induced proliferation
inhibition in ESCC cell, we knocked down the NOXA by siRNA, the results
show that silencing NOXA rescued ixazomib-induced proliferation
inhibition in ESCC cells (Figure 4B, C).
Several studies have evidenced that c-Myc was a prime transcription
factor to transactivate NOXA (Nikiforov et
al., 2007; Knorr et al., 2015). We
determined the protein levels of NOXA and c-Myc in both Kyse150 and
Kyse510 cell lines in response to ixazomib. As shown in Fig. 5A, ESCC
cells express undetectable NOXA protein levels, which were clearly
upregulated following ixazomib treatment. Furthermore, the c-Myc protein
expression followed a trend similar to that observed for NOXA protein
expression. We knocked down the c-Myc by siRNA, same phenomenon can also
be found that reduced c-Myc function rescued ixazomib-induced
proliferation inhibition in ESCC cells (Figure 5B, C). These
observations indicated that c-Myc/NOXA signaling pathways play a major
role in ixazomib induced proliferation inhibition in ESCC cells.