Increase of Fas-induced apoptosis by inhibition of extracellular phosphorylation of Fas receptor in Jurkat cell line

Abstract

Apoptosis signalling through the Fas pathway requires several steps of aggregation of the Fas receptor in the membrane, including aggregation that may occur in the absence of Fas ligand. Association of Fas domains is determinant to signal transmission following Fas ligand binding to a specific domain. The domains involved in Fas aggregation are located in its extracellular region and contain three potential protein kinase C-binding motifs. We therefore studied the possibility that phosphorylation of the extracellular region of Fas might be implicated in the regulation of Fas-mediated apoptosis. Inhibition experiments of extracellular phosphorylation were performed in human Jurkat T leukemia cells with K252b, an impermeant protein-kinase inhibitor. Extracellular phosphorylation of Fas receptor was related to ecto-kinase, as assessed by the [gamma-(32)P] ATP labelling of Fas-116 kDa aggregates, suppressed by K252b inhibitor which significantly increased the sensitivity to Fas-mediated apoptosis. Ecto-PKC involvement was demonstrated by bisindolylmaleimide VIII, a selective inhibitor of protein kinase C which significantly increased both Fas aggregation in the membrane and Fas-mediated apoptosis and by the addition of the PKC pseudo-substrate 19-36 which inhibited the phosphorylation of 116 kDa Fas aggregates. These data support a role for Fas phosphorylation in the decreased sensitivity to apoptosis in the Jurkat T leukemia cell line.

An insight into the sialome of the oriental rat flea, Xenopsylla cheopis (Rots)

“…Extracellular protein phosphorylation/dephosphorylation is known to affect many aspects of cellular signaling [53,54], and is involved in platelet aggregation [55-57]. The conserved basic nature of all flea salivary phosphatases points to interaction with a negatively charged target.…”

Bisindolylmaleimide IX facilitates extrinsic and initiates intrinsic apoptosis in TNF-α-resistant human colon adenocarcinoma COLO 205 cells

“…Our results support the observations of Zhou et al [13] who found that among nine tested Bis derivatives ultimately Bis-VIII and Bis-IX promoted Fas-induced apoptosis rather then Bis-I, Bis-II, Bis-III, Bis-IV, Bis-V, Bis-X and Bis-XI. It is worth to note, that Bisindolylmaleimides were initially described as PKC inhibitors [10,11,28]. In particular, Bis-III is believed to block PKCdependent activation of c-Raf-1, the known downstream target of PKC [18].…”

Autonomic Regulation of Anti-Inflammatory Activities from Salivary Glands

“…Based on molecular modeling it is proposed that feG exerts its antiinflammatory actions by binding to the hydrophobic pocket in the kinase domain that is normally occupied by the hydrophobic motif [82,83]. PKC has a predominant intracellular location, but certain inflammation conditions induce its movement to the extracellular surface where it has possible roles in apoptosis [84,85] and cell adhesion [86,87].…”

“…feG significantly inhibits the binding of peritoneal leukocytes to fibrinogen and fibronectin, and may exert these anti-adhesive actions by interfering with cell adhesion molecules in that: -binding of CD11b (αM integrin) and CD16b (FcγRIIIb: low-affi nity IgG receptor IIIB) of human neutrophils and rat leukocytes [95] is reduced; -expression of CD49d (α4 integrin) on peritoneal neutrophils and circulating leukocytes collected from ovalbumin sensitized rats 24 h aft er challenge [106] is downregulated; modulating PKC activity [82,83]. PKC has been demonstrated to be externalized in several models of infl ammation [84,87], a position where it would be amendable to interaction with SGP-T and homologues for modulation of enzymatic activity and infl ammatory processes.…”