Phosphorylation State-Dependent High Throughput Screening of the c-Met Kinase.

High-throughput screening (HTS) of ~50,000 chemical compounds against phosphorylated and unphosphorylated c-Met, a tyrosine kinase receptor for hepatocyte growth factor (HGF), was carried out in order to compare hit rates, hit potencies and also to explore scaffolds that might serve as potential leads targeting only the unphosphorylated form of the enzyme. The hit rate and potency for the confirmed hit molecules were higher for the unphosphoryalted form of c-Met. While the target of small molecule inhibitor discovery efforts has traditionally been the phosphorylated form, there are now examples of small molecules that target unphosphorylated kinases. Screening for inhibitors of unphosphorylated kinases may represent a complementary approach for prioritizing chemical scaffolds for hit-to-lead follow ups.

Purification of Her-2 extracellular domain and identification of its cleavage site.

The EGF family of receptors belongs to the tyrosine kinase receptor (TKR) family and plays an important role during embryonic and postnatal development and also in the progression of tumors. Her-2/neu/c-erbB-2, a member of the epidermal growth factor receptor family, can be cleaved into a soluble extra cellular domain (ECD) and a membrane-bound stub fragment. Her-2 ECD from a breast cancer cell line SKBR3 was immunopurified and analyzed with matrix-assisted laser desorption ionization (MALDI) and carboxyl terminal amino acid sequencing. A sequence within the juxtamembrane region (only 11 amino acid residues) PAEQR ASP was identified most likely as a primary site of cleavage, PA EQRASP as a minor site, that generate the ECD. The sites of cleavage are within the signature motif P/GX(5-7)P/G highly conserved in the EGF receptor family.

Generation of multiple farnesoid-X-receptor isoforms through the use of alternative promoters.

Bile acid biosynthesis is regulated by both feed-forward and feedback mechanisms involving a cascade of nuclear hormone receptors. Feed-forward regulation of the rate limiting enzyme in bile acid biosynthesis is provided by oxysterols through liver-X-receptor alpha (NR1H3), while feedback regulation is provided by bile acids through farnesoid-X-receptor (FXR) (NR1H4). The Syrian golden hamster provides a useful model for studying lipid metabolism. The hamster metabolizes and transports dietary cholesterol in a similar manner to humans, with the resulting lipid profile being more similar to the human profile than that of other rodent models. Cloning of Fxr from Syrian golden hamster revealed four hamster Fxr splice variants that altered the N-terminal activation domain or the hinge region between the DNA and ligand binding domains. Human genomic sequence and data from hamster Fxr were used to identify and clone a novel human FXR isoform resulting from the use of an alternative promoter. RNA expression analysis indicates that the two human FXR isoforms are differentially expressed in developmental and tissue-specific patterns and are likely to provide a mechanism for cell-specific FXR-dependent transcriptional activity.

Absence of post-translational aspartyl beta-hydroxylation of epidermal growth factor domains in mice leads to developmental defects and an increased incidence of intestinal neoplasia.

The BAH genomic locus encodes three distinct proteins: junctin, humbug, and BAH. All three proteins share common exons, but differ significantly based upon the use of alternative terminal exons. The biological roles of BAH and humbug and their functional relationship to junctin remain unclear. To evaluate the role of BAH in vivo, the catalytic domain of BAH was specifically targeted such that the coding regions of junctin and humbug remained undisturbed. BAH null mice lack measurable BAH protein in several tissues, lack aspartyl beta-hydroxylase activity in liver preparations, and exhibit no hydroxylation of the epidermal growth factor (EGF) domain of clotting Factor X. In addition to reduced fertility in females, BAH null mice display several developmental defects including syndactyly, facial dysmorphology, and a mild defect in hard palate formation. The developmental defects present in BAH null mice are similar to defects observed in knock-outs and hypomorphs of the Notch ligand Serrate-2. In this work, beta-hydroxylation of Asp residues in EGF domains is demonstrated for a soluble form of a Notch ligand, human Jagged-1. These results along with recent reports that another post-translational modification of EGF domains in Notch gene family members (glycosylation by Fringe) alters Notch pathway signaling, lends credence to the suggestion that aspartyl beta-hydroxylation may represent another post-translational modification of EGF domains that can modulate Notch pathway signaling. Previous work has demonstrated increased levels of BAH in certain tumor tissues and a role for BAH in tumorigenesis has been proposed. The role of hydroxylase in tumor formation was tested directly by crossing BAH KO mice with an intestinal tumor model, APCmin mice. Surprisingly, BAH null/APCmin mice show a statistically significant increase in both intestinal polyp size and number when compared with BAH wild-type/APCmin controls. These results suggest that, in contrast to expectations, loss of BAH catalytic activity may promote tumor formation.