Proteomic Profiling of Paclitaxel Treated Cells Identifies a Novel Mechanism of Drug Resistance Mediated by PDCD4

Paclitaxel (PTX) is a widely used
chemotherapeutic drug effective
against numerous cancers. To elucidate cellular pathways targeted
by PTX and identify novel mechanisms of PTX resistance, we used a
SILAC based quantitative proteomic approach to evaluate global changes
of cellular protein abundance in HeLa cells. We identified 347 proteins
involved in a number of biological processes including spindle assembly,
mitotic exit, and extracellular adhesion whose abundance changes upon
PTX treatment. Notably, the tumor suppressor PDCD4 involved in translation
suppression was down-regulated by PTX. We demonstrated that PDCD4
is a cell-cycle regulated protein and that changes in its abundance
are sufficient to alter PTX sensitivity in multiple human cancer cell
lines. Immunoprecipitation of PDCD4–RNA complexes and RT-PCR
revealed that PDCD4 mediated PTX sensitivity acts through its interaction
with mRNA of UBE2S, a ubiquitin K11 linkage conjugating enzyme critical
for mitotic exit. Lastly, high levels of PDCD4 in lung cancer tissues
are positively correlated with the longer overall survival time of
the examined lung cancer patients with PTX involved adjuvant therapy.
Therefore, our proteomic screen for paclitaxel targets not only provided
novel insight into the cellular resistance to paclitaxel via the PDCD4-mitotic
exit regulation axis, but also offered a predictive biomarker for
paclitaxel-based personalized chemotherapy in the treatment of lung
cancer.