Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new serine protease was encoded by a clone isolated from a murine cytotoxic T-lymphocyte complementary DNA library by an RNA-hybridization competition protocol. Complementary transcripts were detected in cytotoxic T lymphocytes, spleen cells from nude mice, a rat natural killer cell leukemia, and in two of eight T-helper clones (both cytotoxic), but not in normal mouse kidney, liver, spleen, or thymus, nor in several tested T- and B-cell tumors. T-cell activation with concanavalin A plus interleukin-2 induced spleen cells to express this gene with kinetics correlating with the acquisition of cytolytic capacity. The nucleotide sequence of this gene encoded an amino acid sequence of approximately 25,700 daltons, with 25 to 35 percent identity to members of the serine protease family. The active site "charge-relay" residues (His57, Asp102, and Ser195 of the chymotrypsin numbering system) are conserved, as well as the trypsin-specific Asp (position 189 in trypsin). A Southern blot analysis indicated that this gene is conserved in humans, mouse, and chicken. This serine protease may have a role in lymphocyte lysis and a "lytic cascade."
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PMID:Cloning of a cDNA for a T cell-specific serine protease from a cytotoxic T lymphocyte. 242 55

An irreversible inhibitor (L-1-tosylamide-2-phenylethyl-chloromethylketone) and substrate (N-acetyl-L-tyrosineethylester) of the neutral serine protease chymotrypsin were evaluated for their effects on the natural killer cell lytic reaction sequence. During direct cell-mediated cytolysis these inhibitors had no effect on natural killer cell binding to target cells but were able to inhibit the "trigger" mechanism which initiates killing. In addition, they inhibited later calcium-dependent events in the lytic reaction and killer cell-independent lysis. These findings suggest that serine proteases may be required during several stages of natural killer cell lysis, including calcium-dependent programming as well as the actual lethal hit.
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PMID:Evidence for involvement of serine proteases in the late stages of the natural killer cell lytic reaction. 354 37

The terminal killer cell-independent lysis (KCIL) stage of the human natural killer (NK) lethal hit is blocked by the protease enzymes trypsin (T), chymotrypsin (CT), and papain (P). The present studies analyze the mechanism of inhibition of KCIL by these enzymes. The pretreatment of effector PBL with T or CT but not P effectively reduced the ability of these cells to mediate NK lysis. This was due at least in part to a reduced ability of the treated NK cells to bind the NK target K562. Pretreatment of K562 cells with T, CT, or P also abolished their ability to serve as targets due to reduced binding ability. These same enzyme-pretreated target cells, however, were unaffected in their ability to bind a natural killer cell-derived cytolytic factor (NKCF) molecule(s), as determined by direct NKCF absorption studies or by their ability to cold target compete for the binding of NKCF to another NKCF-sensitive cell, the L929 fibroblast, thereby indicating that the K562 "target antigen" and the NKCF-receptor are independently expressed structures. Furthermore, NKCF activity, as measured by its ability to kill either K562 or L929 cells, was sensitive to T and CT but resistant to P. These studies indicate that various proteases inhibit NK-KCIL by different mechanisms and suggest that the lethal hit is a complex process. The ability of P to inhibit KCIL but not affect NKCF activity or the target cell NKCF receptor implies that additional NK cell-derived materials may be required in the lethal hit during direct NK cell-mediated cytotoxicity. A model depicting a hypothetical molecular mechanism for human NK cytolysis is presented and discussed.
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PMID:Studies on the mechanism of the human natural killer cell lethal hit: analysis of the mechanism of protease inhibition of the lethal hit. 635 52

These studies analyze the effects of various enzymes on the terminal, killer cell-independent (KCIL) stages of the human natural killer (NK) cytolytic mechanism. The addition of trypsin (T), chymotrypsin (CT), or papain (P) to standard NK reaction mixtures (PBL or LGL and K562 cells) completely ablated cytolytic activity, whereas collagenase was ineffective. Inhibition by T was reversed by preincubation with soybean trypsin inhibitor (SBTI) or fetal calf serum, indicating that the inhibition was indeed due to T. Kinetic analysis with the Ca++ pulse experiment indicated that T, CT, and P inhibited lysis well beyond the Ca++-dependent (EDTA-sensitive) stages and essentially stopped further 51Cr release at the time of addition. This observation was confirmed by the ability of T, CT, and P to block lysis during KCIL of programmed K562 targets that were detached from NK cells by EDTA and were suspended in dextran-containing media. The lysis of K562 cells by natural killer cell-derived cytotoxic factors (NKCF) was also blocked by T and CT but not by P. Inhibition of NKCF activity by T could be reversed by SBTI or fetal calf serum. The ability of T, CT, or P to inhibit the lysis of "programmed" K562 targets during KCIL indicates that the NK lethal hit is an active process mediated by protease-sensitive structures, possibly NKCF, delivered to the target cell by the NK cell during the Ca++-dependent programming steps.
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PMID:Studies on the mechanism of the human natural killer cell lethal hit: evidence for transfer of protease-sensitive structures requisite for target cell lysis. 635 53