Dephosphorylation of p53 during cell death by N-alpha-tosyl-L-phenylalanyl chloromethyl ketone

TPCK targets elements of mitotic spindle and induces cell cycle arrest in prometaphase

The serine protease inhibitor N-alpha-tosyl-epsilon-phenylalanyl chloromethyl ketone (TPCK) has been long used in studies of cellular processes including apoptosis. Depending on the experimental conditions, TPCK either induces or inhibits changes associated with apoptosis but there has been little progress in identifying the relevant targets for TPCK. Our group recently showed that the largest subunit of the RNA polymerase II is one of the intracellular targets of TPCK. The complex effects of TPCK on apoptosis, however, suggested the existence of additional apoptosis-relevant targets in cells. Using our unique polyclonal anti-tosyl antibody, here we report the identification of the mitotic spindle as another intracellular target for TPCK. We also provide data that TPCK-mediated labeling of the mitotic spindle correlates with cell cycle arrest in prometaphase.

N(alpha)-tosyl-L-phenylalanine chloromethyl ketone induces caspase-dependent apoptosis in transformed human B cell lines with transcriptional down-regulation of anti-apoptotic HS1-associated protein X-1

N(alpha)-tosyl-L-phenylalanine chloromethylketone (TPCK) has been widely used to investigate signal transduction pathways that are involved in gene expression and cell survival/cell death. However, contradictory effects of TPCK on apoptosis have been reported, and the underlying signaling events leading to TPCK-induced promotion or prevention of apoptosis are not fully understood. Here, we show that TPCK induces caspase-dependent apoptosis in Epstein-Barr virus (EBV)-transformed human B cell lines with release of pro-apoptotic proteins from mitochondria. TPCK treatment also results in down-regulation of the anti-apoptotic proteins, cIAP1, cIAP2, and HAX-1, and caspase-dependent cleavage of the anti-apoptotic proteins, Bcl-2 and XIAP. Quantitative PCR analysis confirmed that the TPCK-induced down-regulation of HAX-1 occurred at the transcriptional level, and experiments using the specific pharmacological inhibitor, Bay 11-7082, suggested that HAX-1 expression is subject to regulation by the transcription factor, NF-kappaB. B cell lines derived from patients with homozygous HAX1 mutations were more sensitive to TPCK-induced apoptosis when compared with normal donor cell lines. Furthermore, N-acetylcysteine effectively blocked TPCK-induced apoptosis in EBV-transformed B cell lines and prevented the down-regulation or cleavage of anti-apoptotic proteins. Taken together, our studies demonstrate that TPCK induces apoptosis in human B cell lines and exerts multiple effects on pro- and anti-apoptotic factors.

Ser46 phosphorylation of p53 is not always sufficient to induce apoptosis: multiple mechanisms of regulation of p53-dependent apoptosis

The tumor suppressor gene p53 plays a central role in determining cell fate in response to DNA damage; cells may undergo either senescence or apoptosis, depending on cell type. Phosphorylation of Serine 46 (Ser(46)) of p53 is considered to be a primary determinant for the induction of apoptosis, by selectively inducing transactivation of p53 target genes that have proapoptotic function. However, the generality of this mechanism of regulation of p53 remains a matter of debate. We investigated the role of p53 phosphorylation in adriamycin (ADR)-induced apoptosis. We found that Ser(46) was phosphorylated in four different cell lines undergoing ADR-induced senescence, as well as in two different cell lines undergoing ADR-induced apoptosis. Using alanine and glutamic acid substitution mutants of p53 Ser(46), we showed that Ser(46 )phosphorylation is not a prerequisite for induction of the proapoptotic gene AIP1. These results indicate that Ser(46) phosphorylation of p53 is not required for ADR-induced apoptosis.

Another biological effect of tosylphenylalanylchloromethane (TPCK): it prevents p47phox phosphorylation and translocation upon neutrophil stimulation

TPCK (tosylphenylalanylchloromethane), first discovered as a serine protease inhibitor, has been described to affect in diverse systems a number of physiological events probably unrelated to its antiprotease effect, such as proliferation, apoptosis and tumour formation. In the present study, we focus on its inhibition of the neutrophil respiratory burst, an important element of non-specific immunological defence. The superoxide anion-producing enzyme, NADPH oxidase, is quiescent in resting cells. Upon cell stimulation, the redox component, membrane-bound flavocytochrome b558, is activated when the cytosolic factors (p47phox, p67phox and p40phox, as well as the small GTPase Rac) associate with it after translocating to the membrane. This requires the phosphorylation of several p47phox serine residues. The signal transduction events leading to enzyme activation are not completely understood. In the past, the use of diverse protease inhibitors suggested that proteases were involved in NADPH oxidase activation. We suggested previously that TPCK could prevent enzyme activation by the phorbol ester PMA, not due to inhibition of a protease, but possibly to inhibition of the cytosolic factor translocation [Chollet-Przednowed and Lederer (1993) Eur. J. Biochem. 218, 83-93]. In the present work, we show that TPCK, when added to cells before PMA, prevents p47phox phosphorylation and hence its translocation; moreover, when PMA-stimulated cells are incubated with TPCK, p47phox is dephosphorylated and dissociates from the membrane. These results are in line with previous suggestions that the respiratory burst is the result of a series of continuous phosphorylation and dephosphorylation events. They suggest that TPCK leads indirectly to activation of a phosphatase or inactivation of a kinase, and provide the first clue towards understanding the steps leading to its inhibition of NADPH oxidase activation.

Internucleosomal DNA cleavage in apoptotic WEHI 231 cells is mediated by a chymotrypsin-like protease

Although several lines of evidence support a role for serine proteases in apoptosis, little is known about the mechanisms involved. In the present study, we have examined the apoptosis-inducing potential and dissected the death-signalling pathways of N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and N-tosyl-L-lysine chloromethyl ketone (TLCK), inhibitors of chymotrypsin- and trypsin-like proteases, respectively. Our results designate two distinct roles for serine proteases. Firstly, we show that both inhibitors induce biochemical and morphological characteristics of apoptosis, including proteolysis of poly(ADP-ribose) polymerase 1 (PARP-1) and inhibitor of caspase-activated DNase (ICAD), as well as mitochondrial dysfunction, and that their action is abrogated by the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp.fluoromethylketone (z-VAD.fmk). These results suggest that inhibition of anti-apoptotic serine proteases governs the onset of the caspase-dependant apoptotic cascade. Secondly, we also demonstrate the involvement of a serine protease in the terminal stage of apoptosis. We showed that chymotrypsin-like protease activity is required for internucleosomal DNA fragmentation in apoptotic cells. Hence, DNA fragmentation is abrogated in TPCK-pre-treated WEHI 231 cells undergoing apoptosis triggered either by anti-IgM or TLCK. These results indicate that internucleosomal DNA cleavage in apoptotic cells is mediated by a chymotrypsin-like protease.