Synthetic Bryostatin Analogues Activate the RasGRP1 Signaling Pathway

The functional properties of four diacylglycerol (DAG) analogues were compared using cell-signaling assays based on the protein RasGRP1, a DAG-regulated Ras activator. Compounds 1 and 2, synthetic analogues of bryostatin 1, were compared to authentic bryostatin 1 and phorbol 12-myristate-13-acetate (PMA). The two "bryologues" were able to activate RasGRP1 signaling rapidly in cultured cells and isolated mouse thymocytes. They elicited expression of the T cell activation marker CD69 in human T cells. DAG analogues promptly recruited RasGRP1 to cell membranes, but they did not induce RasGRP1 proteolysis. Bryostatin 1 and compounds 1 and 2 appeared to be less potent than PMA at inducing aggregation of mouse thymocytes, a PKC-dependent, RasGRP1-independent response. In addition to sharing potential anticancer properties with bryostatin 1, compounds 1 and 2 might be clinically useful as modulators of the immune system.