The nuclear matrix protein, numatrin (B23), is associated with growth factor-induced mitogenesis in Swiss 3T3 fibroblasts and with T lymphocyte proliferation stimulated by lectins and anti-T cell antigen receptor antibody.

Abstract

Numatrin is a tightly bound nuclear matrix protein (40 kD/pI-5) whose synthesis is markedly and promptly increased in association with cellular commitment for mitogenesis in B lymphocytes. (Feuerstein, N., and J.J. Mond. 1987. J. Biol. Chem. 262:11389-11397). To study whether this event is exclusively associated with proliferation of B lymphocytes, we examined the synthesis of numatrin in T lymphocytes (murine and human) activated by lectins or by anti-T cell antigen receptor monoclonal antibody and in Swiss 3T3 fibroblasts stimulated by growth factors. We showed a close correlation between induction of DNA synthesis and induction of numatrin synthesis in T lymphocytes stimulated by concanavalin A, anti-T cell antigen receptor monoclonal antibody, and IL-2 in murine T cells. Similar results were observed in Swiss 3T3 fibroblasts, thus only combinations of growth factors (insulin/EGF or insulin/B subunit of cholera toxin) or serum, which induced a significant increase in DNA synthesis, were also associated with a significant increase in synthesis of numatrin. Similar to B cells, the increase in numatrin synthesis in fibroblasts was found to occur at early G1 phase. The calcium ionophores, A23187 and ionomycin, previously shown to induce an increase in c-myc and c-fos mRNA levels in fibroblasts, induced a marked increase in the synthesis of a nuclear protein at 80 kD/pI-5 but failed to induce an increase in the synthesis of numatrin indicating that an increase in intracellular Ca++ level is not sufficient for induction of the synthesis of numatrin. This further indicates that the increase in synthesis of numatrin may be more closely correlated with cellular commitment for mitogenesis as compared with other biochemical parameters. Using a polyclonal numatrin antibody we demonstrated that mitogen stimulation is also associated with a marked increase in numatrin abundance, which reached a peak at the onset of S phase and declined at the end of S phase. Evidence is presented to show that numatrin synthesis and abundance is elevated in various lymphoma cell lines. Using indirect immunofluorescence assays we showed that numatrin is abundant in other malignant cells: KB, epidermoid carcinoma, and Hep2 human hepatoma. Immunofluorescence studies further showed that mitogen stimulation of B lymphocytes induced a marked accumulation of numatrin in the nucleoli. This observation is in accord with the recent finding of identity of numatrin with the nucleolar protein B23 (Feuerstein et al. 1988. J. Biol. Chem. 263:10608-10612).(ABSTRACT TRUNCATED AT 400 WORDS)