During vertebrate gastrulation, an epithelial to mesenchymal transition (EMT) is necessary for migration of mesoderm from the primitive streak. We demonstrate that p38 MAP kinase and a p38-interacting protein (p38IP) are critically required for downregulation of E-cadherin during gastrulation. In an ENU-mutagenesis screen we identified the droopy eye (drey) mutation, which affects splicing of p38IP. p38IP(drey) mutant embryos display incompletely penetrant defects in neural tube closure, eye development, and gastrulation. A stronger allele (p38IP(RRK)) exhibits gastrulation defects in which mesoderm migration is defective due to deficiency in E-cadherin protein downregulation in the primitive streak. We show that p38IP binds directly to p38 and is required for p38 activation in vivo. Moreover, both p38 and p38IP are required for E-cadherin downregulation during gastrulation. Finally, p38 regulates E-cadherin protein expression downstream from NCK-interacting kinase (NIK) and independently of the regulation of transcription by Fibroblast Growth Factor (Fgf) signaling and Snail.

Long-term consumption of red meat has been considered a potential risk to gut health, but this is based on clinic investigations, excessive intake of fat, heme and some injurious compounds formed during cooking or additions to processed meat products. Whether intake of red meat protein affects gut bacteria and the health of the host remains unclear. In this work, we compared the composition of gut bacteria in the caecum, by sequencing the V4-V5 region of 16S ribosomal RNA gene, obtained from rats fed with proteins from red meat (beef and pork), white meat (chicken and fish) and other sources (casein and soy). The results showed significant differences in profiles of gut bacteria between the six diet groups. Rats fed with meat proteins had a similar overall structure of caecal bacterial communities separated from those fed non-meat proteins. The beneficial genus Lactobacillus was higher in the white meat than in the red meat or non-meat protein groups. Also, rats fed with meat proteins and casein had significantly lower levels of lipopolysaccharide-binding proteins, suggesting that the intake of meat proteins may maintain a more balanced composition of gut bacteria, thereby reducing the antigen load and inflammatory response in the host.

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Protein kinase C-h (PKCh) plays an important role in T-cell activation via stimulation of AP-1 and NF-jB. Here we report the isolation of SPAK, a Ste20-related upstream mitogen-activated protein kinase (MAPK), as a PKCh-interacting kinase. SPAK interacted with PKCh (but not with PKCa) via its 99 COOH-terminal residues. TCR/CD28 costimulation enhanced this association and stimulated the catalytic activity of SPAK. Recombinant SPAK was phosphorylated on Ser-311 in its kinase domain by PKCh, but not by PKCa. The magnitude and duration of TCR/CD28-induced endogenous SPAK activation were markedly impaired in PKCh-deficient T cells. Transfected SPAK synergized with constitutively active PKCh to activate AP-1, but not NF-jB. This synergistic activity, as well as the receptor-induced SPAK activation, required the PKChinteracting region of SPAK, and Ser-311 mutation greatly reduced these activities of SPAK. Conversely, a SPAKspecific RNAi or a dominant-negative SPAK mutant inhibited PKCh-and TCR/CD28-induced AP-1, but not NF-jB, activation. These results define SPAK as a substrate and target of PKCh in a TCR/CD28-induced signaling pathway leading selectively to AP-1 (but not NF-jB) activation.

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