Soluble T cell immunoglobulin and mucin domain (TIM)-1 and -4 generated by A Disintegrin And Metalloprotease (ADAM)-10 and -17 bind to phosphatidylserine

Abstract

T cell immunoglobulin and mucin domain 1 and 4 (TIM-1 and -4) proteins serve as phosphatidylserine receptors to engulf apoptotic cells. Here we show that human TIM-1 and TIM-4 proteins are targets of A Disintegrin And Metalloprotease (ADAM)-mediated ectodomain shedding resulting in soluble forms of TIM-1 and TIM-4. We identified ADAM10 and ADAM17 as major sheddases of TIM-1 and TIM-4 as shown by protease-specific inhibitors, the ADAM10 prodomain, siRNA and ADAM10/ADAM17 deficient murine embryonic fibroblasts (MEFs). TIM-1 and TIM-4 lacking the intracellular domain were efficiently cleaved after ionomycin- and PMA-treatment, indicating that the intracellular domain was not necessary for ectodomain shedding. Soluble TIM-1 and -4 were able to bind to phosphatidylserine, suggesting that soluble TIM-1 and -4 might act as negative regulators of cellular TIM-1 and -4. In summary, we describe TIM-1 and TIM-4 as novel targets for ADAM10- and ADAM17-mediated ectodomain shedding.

Essential Roles of TIM-1 and TIM-4 Homologs in Adaptive Humoral Immunity in a Zebrafish Model

“…This sTIM-1 protein is released from the cell membranebound TIM-1 proteins by the digestion of metalloproteases at the cleavage site in the mucin domain near the transmembrane region (12,59). However, the existence of other soluble forms of TIM proteins remains unknown, and the function of the sTIM protein has never been reported.…”

Tim-4 in Health and Disease: Friend or Foe?

“…Tim-4 protein can be sheared into soluble Tim-4 (sTim-4) molecule by A Disintegrin and Metalloprotease 10 (ADAM 10) and ADAM 17, without affecting their binding to PS (97). sTim-4 could be detected in serum or bodily fluids, and the changes of sTim-4 might indicate pathological conditions.…”

Regulation of T cell responses by the receptor molecule Tim-3

“…All Tim proteins are expressed on the cell surface and have been shown to function as receptors for soluble or cell-associated ligands. Additionally, certain Tim proteins are produced in soluble forms or can be shed from the cell surface due to cleavage by membrane-associated proteases, suggesting these molecules may also serve as cell-free ligands for other proteins [5-9]. Loci encoding the Tim proteins are found in close proximity to each other within mammalian genomes and genetic studies have uncovered associations between polymorphisms in Tim genes and the development of autoimmune and allergic diseases in humans [10-12].…”