Spontaneous phosphorylation of the receptor with high affinity for IgE in transfected fibroblasts

Receptors with high affinity for IgE, Fc epsilon RI, which had been transfe cted into Chinese hamster ovary fibroblasts exhibit an over 20-fold greater spontaneous phosphorylation at physiological temperatures than the same re ceptors on the widely studied rat mucosal mast cell line, RBL-2H3. This enh anced phosphorylation was not accounted for either by changes in the src-fa mily kinase responsible for the phosphorylation, by reduced activity of pho sphatases, or by spontaneous association of the receptors with microdomains . A variety of approaches failed to detect evidence for stable spontaneous aggregates of the receptor. Whereas the altered posttranslational glycosyla tion of the receptor's principal ectodomain we detected could promote trans ient spontaneous aggregation and explain the observed effect, other changes in the membrane milieu cannot be excluded. The functional consequences of such spontaneous phosphorylation are considered.