Figure 5.

Truncations of the C terminus of StAR abrogate steroidogenesis-enhancing activity. COS-1 cells were transfected with plasmids expressing wild-type StAR and the indicated mutants with the cholesterol side-chain cleavage system. The transfected cells were incubated without (solid bars) or with 22(R)-hydroxycholesterol (open bars), and pregnenolone secretion was determined by radioimmunoassay. Values presented are nanograms per dish per 48 h (means ± SD, n = 3 dishes per treatment) from representative experiments (A and B) or relative to the pregnenolone secretion by cells transfected with the wild-type StAR as means ± SEM (n = 3 separate experiments with three dishes per treatment in each experiment) (C). Pregnenolone secretion by cells transfected with wild-type StAR averaged 439 ng per dish per 48 h from endogenous cholesterol and 850 ng per dish per 48 h in the presence of 22(R)-hydroxycholesterol.