Intracellular Precursor Interleukin (IL)-1α, but Not Mature IL-1α, Is Able to Regulate Human Endothelial Cell Migration in Vitro

The human umbilical vein endothelial cell (HUVEC) has a finite lifespan in vitro , and senescent HUVEC contain elevated levels of the negative growth regulator interleukin (IL)-1α. IL-1α is translated as a signal peptide sequence-less cytosolic 31-kDa precursor (IL-1α p), which undergoes proteolytic activation to release the mature carboxyl terminus 17-kDa protein (IL-1α m). Both the IL-1α p and IL-1α m proteins are biologically active as exogenous cytokines. Interestingly, only IL-1α p contains a nuclear localization sequence between residues 79 and 85. To further study the role of intracellular IL-1α in the regulation of human endothelial cell function, a spontaneous HUVEC transformant was stably transfected with IL-1α p, IL-1α m, and the IL-1α p K82N mutant, which attenuates the nuclear traffic of IL-1α p. Interestingly, the IL-1α p transfectants were found to have a lower migratory potential than either IL-1α m or IL-1α p K82N transfectants, and the addition of the IL-1 receptor antagonist did not alter the migration of these cells. Immunofluorescence microscopy demonstrated that only the IL-1α p transfectants exhibited prominent staining for β-catenin-associated cell-to-cell contacts, as well as pronounced vimentin intermediate filaments and actin cytoskeleton staining. These data suggest that IL-1α p, and not IL-1α m, may function as an intracellular regulator of the migratory capacity of the human endothelial cell and that the nuclear localization sequence present within IL-1α p may be involved in regulating this function.