Arylsulfatase in natural killer cells: its possible role in cytotoxicity.

Abstract

Ultrastructural cytochemistry of natural killer cells enriched by Percoll gradient centrifugation showed them to possess arylsulfatase (aryl-sulfate sulfohydrolase, EC 3.1.6.1). The enzyme was located in vesicles, granules, and the parallel tubular arrays, organelles characteristic for cytotoxic lymphocytes. Biochemically, peak enzyme activity correlated with the Percoll fractions containing cells with cytotoxicity for melanoma target cells. Treatment of natural killer cells with Na2SO4, a competitive inhibitor of arylsulfatase, suppressed cytotoxicity by almost 50%. Electron microscopy of effector-target cell conjugates, which had been permitted to incubate for only 30 min, disclosed numerous arylsulfatase-positive sites at the points of contact between the effector/target cell membranes. Thus, the enzyme was translocated to the surface before lysis of the target cell was morphologically evident. It is postulated that the parallel tubular arrays play a role in this translocation and that arylsulfatase may function in the degradation of cerebroside sulfate ester components of the target cell membrane to initiate the lytic event.A small subpopulation of peripheral blood lymphocytes is able to kill tumor cells in vivo and in vitro without any prior exposure to the neoplasm. The cells endowed with such ability have been called natural killer (NK) cells and their properties are fairly well defined (1, 2). They are recognized as nonadherent, nonphagocytic, large granular lymphocytes that have receptors for the Fc portion of IgG, a weak affinity for sheep erythrocytes, and an ultrastructural marker, the parallel tubular array (PTA) (3, 4). Monoclonal antisera specific for some of their surface antigens also have been developed (5). It is not known how NK cells select their targets and by what mechanism they inflict their lethal effect. However, physical contact between the effector and target cell appears to be necessary for tumor cell lysis to occur. The remarkable interdigitation between the surface membranes of the conjugated cells also has been illustrated repeatedly (4,6,7). However, because it has not been possible to resolve any membrane damage, even on electron microscopy, it is generally assumed that the biochemical alterations that lead to swelling and subsequent lysis of the target cells are beyond morphologic resolution. This has led to biochemical studies intended to show that proteinases associated with NK cells or secreted by them may be responsible for target cell lysis. Indeed, inhibitors of serine proteinases partially inhibit the NK cell effect (4, 6, 8). In our own hands, inhibitors of trypsin-like enzymes and serine esterases have substantially impaired NK cell function (4). A role for free oxygen radicals generated on cell contact has been suggested by others (9, 10). In addition, the translocation of acid hydrolases has been proposed as a possible mechanism involved in cytotoxicity (6, 7). A group of enzymes not heretofore considered to play a role in target cell lysis are the arylsulfa...

Two proteins targeted to the same lytic granule compartment undergo very different posttranslational processing.

“…Previous work had established the subcellular distribution of a number of lysosomal hydrolases in NK cells (12)(13)(14). Although all these enzymes presumably bear phosphomannose, they are present in type II granules and the cortical regions of type I granules, a distribution opposite that of the similarly modified serine proteases.…”

“…Like lysosomes, the granules are acidic (9), although this is also a property of secretory granules (3). In addition, NK granules contain many "classical" lysosomal hydrolases, including acid phosphatase, f3-glucuronidase, and aryl sulfatase (12)(13)(14). Indeed, histochemical assays of these enzymes are often used to identify large granular lymphocytes.…”

“…Indeed, histochemical assays of these enzymes are often used to identify large granular lymphocytes. Interestingly, at least some of the lysosomal enzymes are secreted during cytolysis (14,15), together with the granule-specific proteins. This observation implies that the usual sorting of secretory and lysosomal proteins into separate organelles is incomplete in cytolytic cells, either because the same organelle mediates both functions or because the population of lytic granules is actually composed of two distinct organelles.…”

The putative role of arylsulfatase in interleukin-2- mediated cytotoxicity and interleukin-7-mediated bactericidal activity of natural killer cells

“…It has been shown that AS participates in the cytolytic activity of NK cells towards SRBC [19] and melanoma cells [18]. We studied the cytolytic and bactericidal activities of resting and IL-2-or IL-7-stimulated NK cells against K562, Daudi cells, and E. coli and investigated to what extent AS plays a role in the lytic process of effector cells.…”

“…Several anions are inhibitors of the enzyme, including SO 4 2P , SO 3 2P , and PO 4 3P . The enzyme is known to play a role in granulocytic [17] and NK function [18]. It has been shown that AS is involved in the degradation of cerebroside sulfate esters, likely membrane components of most target cells, and that it participates in the cytolytic activity of NK cells towards melanoma cells [18] and sheep red blood cells (SRBC) [19].…”