TGF-β coordinately activates TAK1/MEK/AKT/NFkB and SMAD pathways to promote osteoclast survival

Abstract

To better understand the roles of TGF-β in bone metabolism, we investigated osteoclast survival in response TGF-β and found that TGF-β inhibited apoptosis. We examined the receptors involved in promotion of osteoclast survival and found that the canonical TGF-β receptor complex is involved in the survival response. The upstream MEK kinase TAK1 was rapidly activated following TGF-β treatment. Since osteoclast survival involves MEK, AKT, and NFκB activation, we examined TGF-β effects on activation of these pathways and observed rapid phosphorylation of MEK, AKT, IKK, IκB, and NFκB. The timing of activation coincided with SMAD activation and dominant negative SMAD expression did not inhibit NFκB activation, indicating that kinase pathway activation is independent of SMAD signaling. Inhibition of TAK1, MEK, AKT, NIK, IKK, or NFκB repressed TGF-β-mediated osteoclast survival. Adenoviral-mediated TAK1 or MEK inhibition eliminated TGF-β-mediated kinase pathway activation and constitutively active AKT expression overcame apoptosis induction following MEK inhibition. TAK1/MEK activation induces pro-survival BclX L expression and TAK1/MEK and SMAD pathway activation induces pro-survival Mcl-1 expression. These data show that TGF-β-induced NFκB activation is through TAK1/MEK-mediated AKT activation, which is essential for TGF-β to support of osteoclast survival.

Transforming Growth Factor-β1 (TGF-β1) Driven Epithelial to Mesenchymal Transition (EMT) is Accentuated by Tumour Necrosis Factor α (TNFα) via Crosstalk Between the SMAD and NF-κB Pathways

“…Images acquired on a Leica confocal microscope (× 63 magnification). All results are normalised to β-tubulin as a loading control that can also be activated by TNFα such as NF-κB, ERK and p38 MAPK [11,13,27,28,[42][43][44][45]. However, in agreement with previous reports, inhibition of p38 or ERK-1 had no effect on TGF-β1 driven or TNFα accentuated EMT [17,18].…”

“…In light of a lack of effect on EMT from inhibition of the MAPK pathway we proceeded to investigate an alternative pathway activated by TNFα, the nuclear factor kappa-lightchain-enhancer of activated B cells (NF-κB) pathway [27,28]. Cells were pre-treated with inhibitors against the inhibitor of nuclear factor kappa-B kinase (IKKβ) subunit of IKK (IKKβ4i or IKKβ6i) and EMT assessed (Figs.…”

Transforming Growth Factor-β1–Mediated Activation of NF-κB Contributes to Enhanced ADAM-12 Expression in Mammary Carcinoma Cells

“…It is possible that in the metastatic cancer cells, TGF-β1 coordinately activates coactivator(s) of NF-κB such as members of the Smad family of transcription factor. Indeed, coordinated action of NF-κB and Smad proteins on their activation by TGF-β1 has been recently reported (42). Smad proteins, although regarded earlier as quintessential tumor suppressor, have now been 7) and with various concentrations of TGF-β1 for 24 h (lanes 3-6 and 8-11), were incubated with a double-stranded 32 P-labeled ADAM-12 DNA probe containing wild-type (lanes 1-6) and mutant (lanes 7-11) NF-κB elements described in Materials and Methods.…”

Bit-1 Mediates Integrin-dependent Cell Survival through Activation of the NFκB Pathway

“…IL-1 activates NFB through the PI3K/AKT/mTOR pathway (32), and osteoclast survival occurs through a TGF-␤ induced TAK1/MEK-mediated AKT activation and NFB signaling cascade (33,34). Vascular endothelial growth factor also has been shown to activate PI3K (35), elevate Bcl-2 expression (35,36), and to enhance NFB mediated survival (37).…”