Comparison of glucocorticoid-induced effects in prolactin-dependent and autonomous rat Nb2 lymphoma cells

Cultured Nb2 node rat lymphoma cells require lactogenic hormone for their proliferation. We reported previously that dexamethasone (Dex) inhibits prolactin (PRL)-induced mitogenesis and, in the absence of mitogen, induces apoptosis of Nb2 cells. Both antiproliferative and cytolytic effects of Dex on Nb2 cells appear to involve glucocorticoid (Type II) receptor mediation. In this study, we compared Dex effects in PRL-dependent Nb2 cells (Nb2) with SFJCD1 (SF), a clone of Nb2 cells that proliferates independently of exogenous PRL. Proliferative assays involved a 72-hr incubation in a chemically defined, serum-free medium where ovine PRL (1 ng/ml) was added to Nb2 cells but not to SF cells. Both cell lines were responsive to the antiproliferative effects of Dex in a dose (6.25-200 nM)-dependent fashion of comparable sensitivity and magnitude. Co-incubation with the glucocorticoid receptor antagonist, RU 486, prevented the antiproliferative effect of Dex in both cell lines. In the same medium devoid of PRL, Dex was cytolytic to Nb2 cells and fragmented DNA in a fashion reflective of apoptosis, but was ineffective in SF cells. A dual chamber incubation system revealed no evidence that SF cells produced cytokines that were mitogenic or anticytolytic to Nb2 cells. Both Nb2 and SF cells fragmented DNA in a fashion indicative of apoptosis in the presence of the Ca2+ ionophore, A23187 (1 microM). These studies reveal a basic difference in glucocorticoid responsiveness between the PRL-dependent Nb2 cell line and its PRL-independent subclone, SF. While both cell lines exhibit functional glucocorticoid receptors and the necessary intranuclear machinery for apoptosis, the pathway mediating the latter is inhibited or dysfunctional in SF cells.