PLK1 and lung cancer: Given that UBE2C is known to couple with APC/C E3 to promote ubiquitylation and degradation of several cell cycle regulators that govern the progression from G2 to M and within the M phase, including PLK1, cyclin B1, and securin (22, 54, 55), we first investigated the involvement of these substrates, but found no significant accumulation upon UBE2C knockdown in multiple lung cancer cell lines harboring a mutant Kras.