Fig. 4: PGRMC1 promotes degradation of select proinsulin mutants.

a HEK 293 T cells expressing the indicated proinsulin mutant were treated with scrambled, PGRMC1, or RTN3 siRNA. Soluble and insoluble fractions were collected as in Fig. 2a, and the samples were subjected to SDS-PAGE and immunoblotted using a Myc antibody. N = 3 independent experiments. b Quantification of proinsulin mutant level from a relative to the scrambled siRNA. Data are represented as mean ± SD. N = 3 independent experiments. One-tailed Standard Student’s t-test was used to determine statistical significance. c HEK 293 T parental and PGRMC1 KO cells expressing A16P-Myc and co-transfected with either an empty vector or HA-PGRMC1 were lysed and subject to SDS-PAGE and immunoblotted as indicated. *The band below the FLAG-PGRMC1 band in lanes 3 and 4 likely represents degraded FLAG-PGRMC1. N = 3 independent experiments. d Quantification of the A16P-Myc level from c relative to parental cells (lane 1). Data are represented as mean ± SD. N = 3 independent experiments. One-tailed Standard Student’s t-test was used to determine statistical significance. e HEK 293 T parental and PGRMC1 KO cells expressing A16P-Myc were treated with cycloheximide for 0, 20, 40, 60, 80 min. Cells were lysed and subjected to SDS-PAGE and immunoblotted as indicated. N = 3 independent experiments. f Quantification of the A16P-Myc level from e relative to t = 0 for either the parental or PGRMC1 KO cells. Data are represented as mean ± SD. N = 3 independent experiments. One-tailed Standard Student’s t-test was used to determine statistical significance. *P ≤ 0.05; **P ≤ 0.005. Source data are provided as a Source Data file. See also Fig. S3.