| Popis: |
Human natural killer (NK) cells are CD56+CD3- large granular lymphocytes of the innate immune system which are characterized by the ability to both directly kill and initiate an immune response to virally infected or malignantly transformed cells. Human NK cells in peripheral blood can be divided into two developmentally and functionally distinct subsets based upon surface expression of CD56. In contrast to the more mature CD56dim NK cell, the less mature CD56bright NK cell is unable to kill malignant cells at rest. We sought to determine the mechanism of this difference in cytolytic activity by exploring changes in gene expression between CD56bright NK cells and CD56dim NK cells. We observed that CD56bright NK cells showed a ~5 fold increase in PTEN protein expression over CD56dim NK cells. Human and murine NK cells overexpressing PTEN demonstrated decreased cytolytic activity and IFN-¿ secretion, with concurrent decreases in their downstream (MAPK and AKT) targets that are critical for cytolysis. Paradoxically, human NK cells with near complete PTEN knockdown also showed decreased cytolytic activity despite elevations in AKT and MAPK. Confocal microscopy revealed that near complete PTEN knockdown results in a disruption of the NK cell’s ability to organize immunological synapse components including decreased adhesion, decreased polarization of the microtubule organizing center toward the target cell and decrease in coalescence of cytolytic granules. Thus, PTEN is differentially expressed in mature human NK cell subsets and our studies suggest it must be expressed at an optimum level to maximize NK cytolytic activity. |
