|
- 积分
- 1
- 威望
- 1
- 包包
- 2112
|
Because a systemic response to lipopolysaccharide (LPS) can be lethal, there are numerous regulatory mechanisms in place to limit its toxic effects. Now, Luke O'Neill and colleagues identify a new pathway that dampens LPS-induced inflammatory responses, involving microRNA-mediated downregulation of the pro-inflammatory protein programmed cell death 4 (PDCD4).
9 c6 d" S& m0 r2 b& J0 S* L, k$ d$ A2 r) z, r+ `3 G4 P, w
In line with previous studies showing that mice deficient in PDCD4 are resistant to the induction of experimental inflammatory diseases, the authors found that PDCD4-deficient mice were less susceptible to LPS-induced death than wild-type mice. Further investigation revealed that PDCD4 expression is modulated following ligation of Toll-like receptor 4 (TLR4) by LPS. LPS stimulation of a macrophage cell line (RAW264.7) or human peripheral blood mononuclear cells first led to a slight increase in PDCD4 expression (after 1 hour) and then to a substantial decrease after 8 and 24 hours. The delayed decrease in PDCD4 expression following LPS stimulation coincided with increased production of the anti-inflammatory cytokine interleukin-10 (IL-10). The known function of PDCD4 as a translational inhibitor is consistent with the finding that LPS-treated PDCD4-deficient cells contained less Il10 mRNA but more IL-10 protein, indicating that the regulation of IL-10 by PDCD4 is at the translational level. In addition, low PDCD4 expression (achieved using Pdcd4-specific small interfering RNA) was associated with less activation of nuclear factor-κB and downstream Il6 transcription after LPS treatment, an effect that is suggested to be secondary to the translation inhibitory function of PDCD4.
6 F% Y' @3 T1 c( ^4 l, A! p( N8 I8 P, U6 A0 O, y
LPS regulates the translation of Pdcd4 mRNA through the induction of miR-21.
3 }7 T- M; f' \5 K L+ X9 |; FSo how is PDCD4 expression downregulated? Previous studies have reported that Pdcd4 mRNA is targeted by the microRNA miR-21, preventing production of PDCD4 protein. Accordingly, the authors found that 4 hours after LPS treatment miR-21 expression was induced, with a tenfold increase detected after 18 hours. This induction of miR-21 expression was dependent on intact TLR signalling capacity. A role for miR-21 expression in the regulation of PDCD4 was consistent with the finding that pre-treatment of RAW264.7 cells with antisense oligonucleotides specific for miR-21, but not control antisense RNA, blocked the LPS-induced decrease in PDCD4 expression. Similarly, a morpholino oligonucleotide designed to block the miR-21-binding site of Pdcd4 abrogated LPS-induced PDCD4 downregulation, confirming that LPS regulates the translation of Pdcd4 mRNA through the induction of miR-21. PDCD4 was also found to be regulated at the protein level through ubiquitylation and degradation by the proteasome, as pre-treatment of RAW264.7 cells with a proteasome inhibitor also blocked the LPS-induced decrease in PDCD4 protein levels after 6 hours.! q/ F" o7 T8 o+ }. Z; f' E
0 Q8 F0 _- k: [4 p' D7 ?Finally, the authors confirmed the link between LPS-induced miR-21 induction, PDCD4 downregulation and increased IL-10 by showing that transfection of RAW264.7 cells with pro-miR-21 (the precursor of mature miR-21) resulted in higher IL-10 production after LPS treatment. This did not occur in PDCD4-deficient cells, confirming that the effect of pro-miR-21 was specifically due to the targeting of Pdcd4 mRNA.
# [0 V6 n: f. [& j
6 `! o; d6 D, c1 fThis newly described role for miR-21 as a negative regulator of inflammation opens up new avenues for therapeutic manipulation of TLR4 activation during sepsis and inflammatory diseases. |
-
总评分: 包包 + 500
查看全部评分
|
发表于 2010-6-6 19:48
