Negative-Feedback Regulation of CD28 Costimulation by a Novel Mitogen-Activated Protein Kinase Phosphatase, MKP6

Abstract

TCR and CD28 costimulatory receptor-cooperative induction of T cell IL-2 secretion is dependent upon activation of mitogen-activated protein (MAP) kinases. Using yeast-hybrid technology, we cloned a novel CD28 cytoplasmic tail (CD28 CYT) interacting protein, MAP kinase phosphatase-6 (MKP6), which we demonstrate inactivates MAP kinases. Several lines of evidence indicate that MKP6 plays an important functional role in CD28 costimulatory signaling. First, in human peripheral blood T cells (PBT), expression of MKP6 is strongly up-regulated by CD28 costimulation. Second, transfer of dominant-negative MKP6 to PBT with the use of retroviruses primes PBT for the secretion of substantially larger quantities of IL-2, specifically in response to CD28 costimulation. A similar enhancement of IL-2 secretion is observed neither in response to TCR plus CD2 costimulatory receptor engagement nor in response to other mitogenic stimuli such as phorbol ester and ionomycin. Furthermore, this hypersensitivity to CD28 costimulation is associated with CD28-mediated hyperactivation of MAP kinases. Third, a retroviral transduced chimeric receptor with a CD28 CYT that is specifically unable to bind MKP6 costimulates considerably larger quantities of IL-2 from PBT than a similar transduced chimeric receptor that contains a wild-type CD28 CYT. Taken together, these results suggest that MKP6 functions as a novel negative-feedback regulator of CD28 costimulatory signaling that controls the activation of MAP kinases.

ZBP-89-induced apoptosis is p53-independent and requires JNK

“…MKPL (MKP6) is a dual-specific MAPK phosphatase that dephosphorylates JNKs as well as ERKs and p38 MAPKs. 35 RNase protection confirmed that reducing ZBP-89 mRNA levels with ZBP-89-specific siRNA upregulates MKP6, while overexpression of ZBP-89 slightly downregulated the expression of this phosphatase (Figure 8b). Considering the kinetics of protein kinase cascades, minor changes in the activity of upstream MKP6 would cause a significant change in the phosphorylation status of the downstream JNK.…”

“…67 Ad-GFP (GFP: green fluorescence protein) and Ad-dnJNK2 (encoding an HA-tagged dominant-negative JNK2 mutant) Ads 68 and the Flag-MKP6-expressing retroviral vector have been described before. 35 …”

Dual-Specificity Phosphatase 14 (DUSP14/MKP6) Negatively Regulates TCR Signaling by Inhibiting TAB1 Activation

“…Also, DUSP14-deficient mice are more susceptible to EAE induction. A previous report (5) showed that DUSP14 interacts with CD28 in overexpressing systems. Primary human peripheral blood T cells transduced with a dominant-negative DUSP14 mutant secrete more IL-2 in response to anti-CD3 plus anti-CD28 costimulation but not anti-CD3 alone or PMA plus ionomycin.…”

“…DUSP14 (also known as MKP6) is an atypical DUSP; DUSP14 contains the consensus C-terminal catalytic domain but lacks the N-terminal CH2 domain. DUSP14 dephosphorylates JNK, ERK, and p38 in vitro (5); however, dominant-negative DUSP14 mutant enhances the activation of JNK and ERK, but not of p38, in the overexpressing system (5). DUSP14 dominant-negative mutant enhances pancreatic b cell proliferation by increasing ERK activation in the overexpressing system (6).…”

Intracellular Signals of T Cell Costimulation

“…CD28 engagement induces massive IL-2 secretion, which is dependent upon the activation of mitogen-activated protein (MAP) kinase (19,38). Using yeast-hybrid technique, a novel CD28 cytoplasmic tail (CD28 CYT) interacting protein, the MAP kinase phosphatase-6 (MKP6) was isolated, which showed to inactivate MAP kinases, so it is associated with cytokine secretion (39). Besides MKP6 protein, the YMNM motif on the CD28 cytoplasmic domain is also known as a binding site for PI3K and growth factor receptor-bound protein 2 (Grb-2) hence is considered to be important for CD28-induced IL-2 secretion (40,41).…”