Monocyte 15-Lipoxygenase Expression Is Regulated by a Novel Cytosolic Signaling Complex with Protein Kinase C δ and Tyrosine-Phosphorylated Stat3

Abstract

Our previous studies demonstrated that IL‐13‐induced 15‐lipoxygenase (15‐LO) expression in human monocytes is regulated by the activation of both Stat1 and Stat3 and by PKCδ. IL‐13 stimulated the phosphorylation of Stat3 on both Tyr705 and Ser727. In this study we show that IL‐13 induces the association of PKCδ with Stat3, not with Stat1, and is required for Stat3S727 phosphorylation. We found that the IL‐13‐dependent, novel signaling complex of PKCδ and Stat3 occurs almost exclusively in the cytosol and that the Stat3 in the complex is tyrosine phosphorylated. From our preliminary results we hypothesized that tyrosine phosphorylation was required for Stat3 interaction with PKCδ and subsequent PKCδ‐dependent phosphorylation of Stat3S727. Using an efficient transfection protocol for human monocytes, we showed that expression of Stat3 containing a mutation in Y705 inhibited the association of PKCδ with Stat3 and blocked Stat3S727 phosphorylation whereas transfection with wild‐type Stat3 did not. Our results indicate that Stat3Y705 phosphorylation is a prerequisite for the IL‐13–stimulated association of Stat3 with cytosolic PKCδ and the Stat3S727 phosphorylation. Furthermore, by transfecting monocytes with Stat3 containing mutations in Y705 and S727 or with wild type Stat3, we demonstrated that both Stat3 tyrosine and serine phosphorylations are required for optimal binding of Stat3 with DNA as well as for maximal expression of 15‐LO, an important regulator of inflammation and apoptosis. (This work was funded by HL51068)

Protein kinase C-δ is involved in the inflammatory effect of IL-6 in mouse adipose cells

“…Another possibility is that PKCδ is important for stabilising STAT3 binding to gp130. Reports have shown that PKCδ associates with Tyr-705-phosphorylated STAT3 in the cytoplasm [22,36] and that it can also bind and phosphorylate gp130 [37]. We have also detected an interaction between STAT3 and PKCδ by co-immunoprecipitation, but this interaction was not altered by either IL-6 or rottlerin (ESM Fig.…”

PKC-δ inhibitors sustain self-renewal of mouse embryonic stem cells under hypoxiain vitro

“…These studies cannot exclude the possibility that PKC-δ inhibitors may directly modulate the LIFR-STAT3 pathway, as well as destabilizing the HIF-1α stability. However, other studies have investigated that rottlerin does not affect both STAT1 Tyr 701 and STAT3 Tyr 705 phosphorylation in human peripheral blood monocytes (Bhattacharjee et al, 2006). Hence, taken together, we concluded that PKC-δ inhibitors may not regulate the LIFR-STAT3 via direct phosphorylation of STAT3, but mediate the destabilization of HIF-1α protein, resulting in maintenance of pluripotency in mESCs.…”

From Macrophage Interleukin-13 Receptor to Foam Cell Formation

“…We have previously published that IL-13-mediated Stat3 tyrosine phosphorylation is required for the formation of a molecular signaling complex (signalosome) containing p38MAPK (data not shown), PKC␦, and tyrosine-phosphorylated Stat3 (27). The signalosome was shown to regulate Stat3 Ser-727 phosphorylation and Stat3-dependent transcription of 15-LO (27).…”

“…The signalosome was shown to regulate Stat3 Ser-727 phosphorylation and Stat3-dependent transcription of 15-LO (27). Based on these results we tested whether ␣ M ␤ 2 integrin activation or clustering affected IL-13-stimulated Stat3 tyrosine phosphorylation, Stat3 association with PKC␦, and Stat3 Ser-727 phosphorylation to determine whether integrin activation affected these aspects of IL-13 signaling.…”