Mitochondrial Proteomic Analysis of Cisplatin Resistance in Ovarian Cancer

Epithelial ovarian cancer (EOC) is the leading cause
of death among
women with gynecologic malignancies and accounts for approximately
6% of cancer deaths among women. Cisplatin and its analogues form
the backbone of the most active chemotherapy regimens in advanced
EOC; however, development of platinum resistance is common and typically
marks a transition in which curing the patient is no longer possible.
An emerging theme in many cancers is that mitochondrial dysfunction
contributes to an aggressive carcinogenic phenotype. We hypothesized
that changes in the mitochondrial proteome are required to support
development of cisplatin resistance in human EOC. To investigate this
hypothesis, an organellar proteomics approach was utilized to quantify
alterations in protein abundance in mitochondria enriched from isogenic
cisplatin-sensitive (A2780) and -resistant (A2780-CP20) human EOC
cells. Protein isolates from mitochondria-enriched fractions were
analyzed by high resolution liquid chromatography–tandem mass
spectrometry (LC–MS/MS), and relative abundance of identified
proteins was quantified by spectral counting. Pathway analyses revealed
significant increases in notch signaling pathways, cell survival,
and alternate apoptotic pathways in the A2780-CP20 subtype. Among
the alterations identified in the mitochondrial proteomic composition
in cisplatin-resistant EOC cells, activated leukocyte cell adhesion
molecule (AKAP12) and A kinase anchoring protein 12 (AKAP12) were
elevated, while nestin was diminished in the mitochondrial fraction
of A2780-CP20 relative to A2780. This was verified by immunoblot analysis.
These results confirm that important changes in the mitochondrial
proteome, many of which promote evasion of apoptosis and tumor invasiveness
and metastasis, are present in cisplatin-resistant EOC.