MIDN is necessary for parkin expression in PC12 cells. (a) MIDN, parkin, TH, and GAPDH protein levels in MIDN-positive and -negative PC12 cells were examined by Western blotting (left panel). The density of the parkin and TH bands was normalized to that of GAPDH, and these ratios were expressed as a percentage of MIDN-positive cells (middle and right panels). Parkin protein expression was significantly inhibited by MIDN knockout (*p < 0.05, n = 6) whereas TH protein expression was not significantly changed (n = 6). (b) Gene expression levels of MIDN and parkin in MIDN-positive and -negative PC12 cells were examined by qRT-PCR. Significant differences in both MIDN and parkin gene expression were observed between MIDN-positive and -negative cells (*p < 0.05, n = 6).