Human Tribbles, a Protein Family Controlling Mitogen-activated Protein Kinase Cascades

Abstract

Control of mitogen-activated protein kinase (MAPK)cascades is central to regulation of many cellular responses. We describe here human tribbles homologues (Htrbs) that control MAPK activity. MAPK kinases interact with Trbs and regulate their steady state levels. Further, Trbs selectively regulate the activation of extracellular signal-regulated kinases, c-Jun NH 2 -terminal kinases, and p38 MAPK with different relative levels of activity for the three classes of MAPK observed depending on the level of Trb expression. These results suggest that Trbs control both the extent and the specificity of MAPK kinase activation of MAPK. Mitogen-activated protein kinase (MAPK)1 cascades control the activity of three sets of effector protein kinases (extracellular signal-regulated protein kinases (ERKs), Jun kinases (JNKs), and p38s). The central element in each MAPK pathway is a module of three protein kinases, MAPKK kinase, MAPKK, and MAPK (1). The three sets of effector MAPK differ in type of activating stimulus: JNKs and p38/HOG-1 primarily respond to stress (e.g. heat shock), and ERKs primarily respond to mitogens. However, a stimulus can activate more than one class of MAPK; the contribution of each pathway is cell typedependent, and MAPK pathways can both synergize and antagonize. This is caused in part by regulatory proteins influencing signaling by a range of mechanisms including scaffolding (e.g. JIP-1, STE5), regulating localization (e.g. Ksr), or recruitment to targets (e.g. 14-3-3 proteins) (2-4). Here we describe a novel family of MAPK control proteins, homologues of fly tribbles.Drosophila tribbles was shown to regulate String activity and hence mitosis during ventral furrow formation (5-8). A canine Trb-2-like protein has been described in the literature as a transiently expressed, mitogen induced, and highly labile cytoplasmic phosphoprotein, but its biological function was not characterized (9, 10). Rat Trb was shown to be rapidly upregulated during neuronal cell apoptosis (11). Recently Trb-3 has been reported to regulate Akt activation in liver by insulin (12) and regulate ATF4 activity (13,14). We show here that Trbs bind to MAPKK and regulate MAPK activation suggesting that Trb function may be broader than reported previously. , FLAG-MEK-1 (16), , and LHRE-TK-luc (18) were described earlier. V12 Ras was a gift of J. Downward. pAP-1 luc, pNFB luc, pFR luc, pFA-CHOP, pFA2-Elk-1, pMEKK-1 pMEK-1, and pMEK-3 were part of the PathDetect system (Stratagene). Quantitative real time-PCR was performed to characterize the expression profile of human tribbles genes by using the Human Rapid-Scan panel (Origene). MRNA levels are expressed as relative units normalized for glyceraldehyde-3-phosphate dehydrogenase expression. MATERIALS AND METHODS PlasmidsCell 85060701) and NIH 3T3 cells were maintained in Dulbecco's modified Eagle's medium with 10% fetal calf serum and penicillin-streptomycin. Raw cells were cultured in RPMI 1640 medium supplemented with 10% fetal calf serum and penicillin-streptomycin. Cells (1.5 ϫ ...

Multiple signaling pathways involved in stimulation of osteoblast differentiation by N-methyl-D-aspartate receptors activation in vitro

“…Expression of Trib3 was found to be PI3K-dependent in prostate [43] . Furthermore, it has been suggested that the tribbles protein family is involved in regulation of the MAP kinase pathway [44] . Nuclear factor-κB (NF-κB) is a ubiquitous heterodimeric transcription factor that regulates inflammation and cell survival and differentiation [45,46] .…”

Developmental roles of tribbles protein family members

“…In the cytoplasm, Tribs direct the proteosomal degradation of key signaling proteins, including ACC1 (Qi et al, 2006), SMURF1, FoxO (Matsumoto et al, 2006) and C/ EBP Naiki et al, 2007;Selim et al, 2007;Dedhia et al, 2010;Keeshan et al, 2010;Grandinetti et al, 2011). Also in the cytoplasm, Tribs bind to inactivate LAP (Naiki et al, 2007), MKKs (Kiss-Toth et al, 2004;Wang et al, 2011), and Akt (Du et al, 2003).…”

“…Posttranscriptional regulation of Trib3 variants is suggested by the occurrence of upstream open reading frames (Ord et al, 2009). Finally, even the levels of one isoform may exert distinct influences: low levels of Trib3 are reported to inhibit p38 and enhance Jnk and ERK activation, while at higher levels of Trib3, all three kinases are inhibited (Kiss-Toth et al, 2004). This outcome implies that Trib isoform levels relative to the levels of key partners may dictate tissue-specific effects.…”

Loss of Tribbles pseudokinase-3 promotes Akt-driven tumorigenesis via FOXO inactivation

“…8 Tribbles pseudokinase-3 (TRIB3; also named TRB3, NIPK and SKIP3) has been proposed to interact with several proteins, including the transcription factors activating transcription factor 4 (ATF-4) and CHOP 9 as well as with several MAPKs. 10 TRIB3 has also been shown to interact and inhibit AKT, 11 which has been suggested to suppress insulin signaling. 11,12 In addition, administration of different anticancer agents promotes cancer cell death via TRIB3 upregulation and the subsequent inhibition of Akt.…”