PITUITARY FOLLICULAR CELLS SECRETE AN INHIBITOR OF AORTIC ENDOTHELIAL-CELL GROWTH - IDENTIFICATION AS LEUKEMIA INHIBITORY FACTOR

Medium conditioned by bovine pituitary follicular cells paradoxically inhibits the growth of adult bovine aortic endothelial (ABAE) cells at dilutions that are instead mitogenic to adrenal cortex capillary endothelial (ACCE) cells, suggesting that follicular cells secrete a growth inhibitor with a selectivity for ABAE cells. The ABAE cell inhibitory activity was purified to apparent homogeneity by a combination of size-exclusion chromatography, ion-exchange chromatography, and two reversed-phase steps on a C4 column. Microsequencing of the purified material revealed a single NH2-terminal amino acid sequence, identical to that of leukemia inhibitory factor (LIF), a glycoprotein originally identified by its ability to inhibit the growth of MT1 mouse leukemia cells and subsequently found to have numerous effects. Recombinant human LIF inhibited the growth of ABAE cells as effectively as transforming growth factor-beta (TGF-beta-1). However, it failed to inhibit markedly the growth of ACCE cells, whereas TGF-beta-1 dramatically inhibited their growth. Recombinant human LIF also failed to induce a significant angiogenic response in the chicken chorioallantoic membrane, indicating that, unlike TGF-beta, LIF probably does not induce the release of direct-acting angiogenic factors from inflammatory cells. The presence of LIF in follicular cells may relate to the peculiar vascular organization of the pituitary gland, where no arteries reach the pars distalis and all of the blood supply to this area is by capillaries.