6 research outputs found
Mechanism of Activation and Inhibition of the HER4/ErbB4 Kinase
SummaryHER4/ErbB4 is a ubiquitously expressed member of the EGF/ErbB family of receptor tyrosine kinases that is essential for normal development of the heart, nervous system, and mammary gland. We report here crystal structures of the ErbB4 kinase domain in active and lapatinib-inhibited forms. Active ErbB4 kinase adopts an asymmetric dimer conformation essentially identical to that observed to be important for activation of the EGF receptor/ErbB1 kinase. Mutagenesis studies of intact ErbB4 in Ba/F3 cells confirm the importance of this asymmetric dimer for activation of intact ErbB4. Lapatinib binds to an inactive form of the ErbB4 kinase in a mode equivalent to its interaction with the EGF receptor. All ErbB4 residues contacted by lapatinib are conserved in the EGF receptor and HER2/ErbB2, which lapatinib also targets. These results demonstrate that key elements of kinase activation and inhibition are conserved among ErbB family members
Insertion of methylene units into the turn segment of designed β-hairpin peptides
The effect of insertion of methylene groups into the turn segment of β-hairpin peptides has been investigated in the model sequence Boc-Leu-Val-Val-DPro-δ-Ava-Leu-Val-Val-OMe. This sequence is related to the previously well-characterized model β-hairpin octapeptide, Boc-Leu-Val-Val-DPro-Gly-Leu-Val-Val-OMe. Replacement of Gly by δ-Ava (δ-aminovaleric acid) formally corresponds to expansion of the turn segment from a two-residue loop to a three-residue loop. Backbone proton chemical shifts, vicinal coupling constants, and circular dichroism spectra for the two peptides are virtually indistinguishable. Nuclear Overhauser effects corresponding to short cross-strand interproton distances confirm that the registry of the β-hairpin structure is maintained in the δ-Ava peptide. Restrained molecular dynamics simulations, using experimental constraints, yield two structural families that are consistent with the NOE data. Both families correspond to β-hairpin conformations and differ only in the backbone torsion angles at the δ-Ava residue
SRF Phosphorylation by Glycogen Synthase Kinase-3 Promotes Axon Growth in Hippocampal Neurons
The growth of axons is an intricately regulated process involving intracellular signaling cascades and gene transcription. We had previously shown that the stimulus-dependent transcription factor, serum response factor (SRF), plays a critical role in regulating axon growth in the mammalian brain. However, the molecular mechanisms underlying SRF-dependent axon growth remains unknown. Here we report that SRF is phosphorylated and activated by GSK-3 to promote axon outgrowth in mouse hippocampal neurons. GSK-3 binds to and directly phosphorylates SRF on a highly conserved serine residue. This serine phosphorylation is necessary for SRF activity and for its interaction with MKL-family cofactors, MKL1 and MKL2, but not with TCF-family cofactor, ELK-1. Axonal growth deficits caused by GSK-3 inhibition could be rescued by expression of a constitutively active SRF. The SRF target gene and actin-binding protein, vinculin, is sufficient to overcome the axonal growth deficits of SRF-deficient and GSK-3-inhibited neurons. Furthermore, short hairpin RNA-mediated knockdown of vinculin also attenuated axonal growth. Thus, our findings reveal a novel phosphorylation and activation of SRF by GSK-3 that is critical for SRF-dependent axon growth in mammalian central neurons
mTORC1 Activation Regulates β-Cell Mass and Proliferation by Modulation of Cyclin D2 Synthesis and Stability*S⃞
Growth factors, insulin signaling, and nutrients are important regulators
of β-cell mass and function. The events linking these signals to the
regulation of β-cell mass are not completely understood. The mTOR pathway
integrates signals from growth factors and nutrients. Here, we evaluated the
role of the mTOR/raptor (mTORC1) signaling in proliferative conditions induced
by controlled activation of Akt signaling. These experiments show that the
mTORC1 is a major regulator of β-cell cycle progression by modulation of
cyclin D2, D3, and Cdk4 activity. The regulation of cell cycle progression by
mTORC1 signaling resulted from modulation of the synthesis and stability of
cyclin D2, a critical regulator of β-cell cycle, proliferation, and mass.
These studies provide novel insights into the regulation of cell cycle by the
mTORC1, provide a mechanism for the antiproliferative effects of rapamycin,
and imply that the use of rapamycin could negatively impact the success of
islet transplantation and the adaptation of β-cells to insulin
resistance