Role of NKLAM in the Killing of Tumor Cells

摘要

NKLAM (Natural Killer Lytic Associated Molecule) is a novel protein within the cytolytic granules of natural killer (NK) cells and cytotoxic T cells (CTL). Reduction in NKLAM expression decreases the cytotoxicity of these cells, indicating a role of NKLAM in killing. NKLAM possesses three zinc binding RING finger domains, motifs involved in protein-protein interactions. NKLAM has been found to bind to three proteins, URKL-l (Uridine Kinase Like-i), and E2 ligases UbcH8 (human ubiquitin conjugate 7) and UbcH8. The interactions between NKLAM and URKL-l, as well as the ubiquitin conjugates, have been shown to involve the second cysteine rich domain of NKLAM. The interaction between NKLAM and UbcH8 has also been found to occur endogenously. Confocal microscopy shows that NKLAM and URKL-l are co-localized in the cytoplasm of 293 cells when they are transfected together, however, transfected separately URKL-l is found in the nucleus and NKLAM remains in the cytoplasm. We also identify increased degradation of URKL-l in the presence of NKLAM compared to the level of degradation occurring with the NKLAM constructs. These results solidify our finding that NKLAM acts as an E3 ligase toward URKL-l.