We have previously identified midnolin (MIDN) as a genetic risk factor for Parkinson's disease. However, the molecular entity of MIDN that regulates neuronal phenotypes remains unclear. To investigate the molecular function of MIDN, we examined proteins associated with MIDN in PC-12 cells. We performed LC-MS/MS analysis of flag-immunoprecipitated samples from the nuclear fraction of PC-12 cells expressing flag-tagged MIDN (MIDN-Flag) or pcDNA3.1(+) (the empty vector) treated with MG132 (5 μM, 6 h) and nerve growth factor (500 ng/mL, 2 h).