Effect of 1,25‐dihydroxyvitamin D 3 on mouse mammary tumor (GR) cells: Evidence for receptors, cellular uptake, inhibition of growth and alteration in morphology at physiologic concentrations of hormone

Mammary glands are target tissues for 1,25‐dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ). We have examined a mouse mammary tumor cell line (GR) for receptors of 1,25(OH) 2 D 3 and have examined alterations in the growth and morphology of these cells in response to 1,25(OH) 2 D 3 . GR cells contain a high affinity (Kd ∼ 10 −11 ), lowcapacity receptor with a high specificity for 1,25(OH) 2 D 3 . The 1,25(OH) 2 D 3 receptor in GR cells has a sedimentation coefficient of 3.5 and elutes from DEAE cellulose columns with ∼ 0.15 M KCI. These properties of the receptor are similar to those reported for other 1,25(OH) 2 D 3 receptors. 1,25(OH) 2 D 3 is internalized by GR cells in situ and specifically bound 1,25(OH) 2 D 3 is found predominantly, if not entirely, in the nucleus as determined by cell fractionation and autoradiographic techniques. The incubation of GR cells in culture for 7 days with 1,25(OH) 2 D, markedly alters cell growth. Cell growth is retarded in a dose‐dependent manner; physiologic concentrations (10 −10 M ) of l,25(OH) 2 D 3 retard cell growth by approximately 50%. In addition, GR cells incubated with 10 −9 to 10 −8 M 1,25(OH) 2 D 3 undergo marked morphological changes. The incubation of GR cells with other vitamin D metabolites such as 25‐hydroxyvitamin D 3 (25(OH)D 3 ) at a concentration of 10 −9 M does not significantly alter cell growth or morphology. The presence of high affinity receptors for 1,25(OH) 2 D 3 , the specific internalization of 1,25(OH) 2 D 3 predominantly into the nuclei, and the significant effects of physiological concentrations of 1,25(OH) 2 D 3 on cell growth suggest a direct, specific, nuclear effect of 1,25(OH) 2 D 3 on GR cells. The mouse mammary tumor model might be useful in examining the effect of 1,25(OH) 2 D 3 on tumor formation.