Somatostatin antisense oligodeoxynucleotide-mediated stimulation of lymphocyte proliferation in culture

We have previously shown that somatostatin (SRIF) is synthesized in B and T lymphocytes of rat spleen and thymus and released into the medium of cultured lymphocytes. To determine the role of SRIF in the control of lymphocyte proliferation, the expression of SRIF in normal lymphocytes was inhibited using a 3'-terminal phosphorethioate-modified antisense oligonucleotide complementary to a sequence that includes the translation start site of the rat SRIF messenger RNA. Spleens were obtained from adult male rats, and their lymphocytes were cultured for 24 or 72 h to measure SRIF content and cell proliferation, respectively. For the proliferation studies, [H-3]thy midine was incorporated during the final 18 h. The lymphocytes were incubated with 15-30 mu g/ml SRIF antisense and control antisense. SRIF antisense (25 mu g/ml) increased lymphocyte proliferation 15-fold (P not less than or equal to 0.001), reaching a plateau (25- to 30-fold increase) between 25-30 mu g/ml SRIF antisense. SRIF was extracted from lymphocytes and measured by RIA. Levels of SRIF content were almost undetectable with 30 mu g/ml antisense and were significantly lower (P < 0.01) with 25 mu g/ml antisense. When RC 160 (10(-5) M), a SRIF agonist analog, was used in the incubation, the stimulation of cell proliferation exerted by the SRIF antisense was completely abolished. Control antisense had no effect on proliferation or SRIF content. These findings indicate that 1) lymphocytes in culture are able to incorporate SRIF antisense; and 2) SRIF antisense inhibits the expression of lymphocytic SRIF, which leads to lymphocyte proliferation. In conclusion, cell proliferation is dramatically increased by eliminating the expression of SRIF from the lymphocytes, which indicates that in vitro SRIF is acting in a paracrine and/or autocrine fashion to inhibit lymphocyte proliferation.