Autocrine interaction between prolactin and its receptor occurs intracellularly in the 235-1 mammotroph cell line

We have previously demonstrated that PRL acts as an autocrine growth factor in the pituitary tumor GH3 cell line. In this study we present evidence that the 235-1 cell line also uses PRL as an autocrine growth factor, and that in this case interaction between PRL and its receptor occurs intracellularly. First, the PRL produced by 235-1 cells was shown to be capable of initiating a proliferative response by placement in the Nb2 bioassay. Second, PRL receptors were demonstrated to be present, but, unusually, primarily in the Golgi complex by light and electron microscope immunocytochemistry. Incubation of the cells in anti-PRL had no effect on 235-1 cell proliferation until interleukin-1 treatment caused the PRL receptors to move to the cell surface, whereupon cell proliferation was inhibited. Specific interference with PRL biosynthesis in noninterleukin-1-treated cells also inhibited cell proliferation. Thus, the essential elements of an autocrine loop are present and can be demonstrated to be functional by antibody inhibition of growth after movement of the receptors to the cell surface and by antisense inhibition of growth with the receptors in their normal intracellular location.