Quantitative proteomics reveals a novel role of karyopherin alpha 2 in cell migration through the regulation of vimentin-pErk protein complex levels in lung cancer.

Karyopherin alpha 2 (KPNA2) is overexpressed in various human cancers and is associated with cancer invasiveness and poor prognosis. Herein, to understand the essential role of KPNA2 protein complexes in cancer progression, we applied stable isotope labeling with amino acids in cell culture (SILAC)-based quantitative proteomic strategy combined with immunoprecipitation (IP) to investigate the differential KPNA2 protein complexes in lung adenocarcinoma cell lines with different invasiveness potentials. We found that 64 KPNA2-interaction proteins displayed a 2-fold difference in abundance between CL1-5 (high invasiveness) and CL1-0 (low invasiveness) cells. Pathway map analysis revealed that the formation of complexes containing KPNA2 and cytoskeleton-remodeling-related proteins, including actin, beta tubulin, tubulin heterodimers, vimentin, keratin 8, keratin 18, and plectin, was associated with cancer invasiveness. IP demonstrated that the levels of KPNA2-vimentin-pErk complexes were significantly higher in CL1-5 cells than in CL1-0 cells. The KPNA2-vimentin-pErk complex was also up-regulated in the advanced stage compared with the early-stage lung adenocarcinoma tissues. Importantly, the levels of pErk as well as cell migration ability were significantly reduced in KPNA2-knockdown cells; however, migration was restored by treatment with pErk phosphatase inhibitors. Collectively, our results demonstrate the usefulness of a SILAC-based proteomic strategy for identifying invasiveness-associated KPNA2 protein complexes and provide new insight into the KPNA2-mediated modulation of cell migration.