Expression of spectrin in nonerythroid cells

Abstract

spleen cells to the T-cell mitogens concanavalin A and phytohemagglutimin. The ,f3-endorphin effect was dose-dependent at concentrations similar to those found in rat plasma. ,&Endorphin had no effect on resting, unstimulated spleen cells. Recently, Schweigerer et al. (Nature 296, 572-574, 1982) reported specific nonopiate binding of &-endorphin to both terminal complexes of human complement: the cytolytic, membrane-derived C5b-9(m) complex, and the cytolytically inactive, serum-derived SC5b-9 complex. These observations suggest that ,L?-endorphin may play an important role in the immune system. For the last few years, more than 60 /I-endorphin analogs have been synthesized by the solid-phase method and characterized. Their biological activities have been assessed by opiate receptor binding, inhibition of electrically stimulated contraction of guinea pig ileum preparation and mouse tail-flick analgesic and radioimmunoreactivity assays. These data, recently reviewed (Li, Hormonal Proteins and Peptides 10, l-34, 19811, suggest the presence of three binding sites in the /I-endorphin molecule, as shown in Figure 2. The first site (15 receptors) is located in the Met-enkephalin segment, and the second site (p receptor) resides in the COOH-terminal segment. The middle segment is the antibody-binding site. Among the synthetic ,&endorphin analogs, /I-endorphin-(6-31) (an analog without the Met-enkephalin segment) exhibits interesting properties. It possesses minimal analgesic potency and ileal opiate activity. As mentioned above, P-endorphin-(6-31) binds to the opiate receptor in the neuroblastoma N18TG2 cells. When P-endorphin-(6-31) is injected together with P-endorphin, it inhibits ,&endorphin-induced analgesia. It may be recalled that a segment of human ACTH [a,,-ACTH-(6-3811 is an inhibitor of ACTH action (Li et al., PNAS 75, 4306-4309, 1978). The concept that a peptide segment inside the amino acid sequence of a hormone is an inhibitor of the hormone itself may turn out to be a general phenomenon in biologically active polypeptides.