NADH Dehydrogenase Ubiquinone 1 Alpha Subcomplex Assembly Factor 4 (NDUFaF4)

Quiescent Nb2-11 cells synchronized in G0-G1 had reduced Hrpap20 expression compared with exponentially proliferating cultures. Addition of mitogenic concentrations of prolactin to stationary cells increased Hrpap20 mRNA and protein and stimulated serine phosphorylation of Hrpap20. Stable transfection of Hrpap20 into Nb2-11 cells increased proliferation and inhibited apoptosis induced by lactogen (CSH1) deprivation. In a hormone-independent and highly malignant Nb2 subline, constitutive expression of Hrpap20 was markedly reduced by exposure of cells to the differentiating agents butyrate, retinoic acid, and vitamin D3. Expression of HRPAP20 was also observed in quiescent human breast carcinoma cells, and addition of prolactin increased HRPAP20 during G1 cell cycle progression.