Protein tyrosine kinases (PTKs) coordinate a broad spectrum of cellular responses to extracellular stimuli and cell–cell interactions during development, tissue homeostasis, and responses to environmental challenges. Thus, an understanding of the regulatory mechanisms that ensure physiological PTK function and potential aberrations of these regulatory processes during diseases such as cancer are of broad interest in biology and medicine. Aside from the expected role of phospho-tyrosine phosphatases, recent studies have revealed a critical role of covalent modification of activated PTKs with ubiquitin as a critical mechanism of their negative regulation. Members of the Cbl protein family (Cbl, Cbl-b and Cbl-c in mammals) have emerged as dominant “activated PTK-selective” ubiquitin ligases. Structural, biochemical and cell biological studies have established that Cbl protein-dependent ubiquitination targets activated PTKs for degradation either by facilitating their endocytic sorting into lysosomes or by promoting their proteasomal degradation. This mechanism also targets PTK signaling intermediates that become associated with Cbl proteins in a PTK activation-dependent manner. Cellular and animal studies have established that the relatively broadly expressed mammalian Cbl family members Cbl and Cbl-b play key physiological roles, including their critical functions to prevent the transition of normal immune responses into autoimmune disease and as tumor suppressors; the latter function has received validation from human studies linking mutations in Cbl to human leukemia. These newer insights together with embryonic lethality seen in mice with a combined deletion of Cbl and Cbl-b genes suggest an unappreciated role of the Cbl family proteins, and by implication the ubiquitin-dependent control of activated PTKs, in stem/progenitor cell maintenance. Future studies of existing and emerging animal models and their various cell lineages should help test the broader implications of the evolutionarily-conserved Cbl family protein-mediated, ubiquitin-dependent, negative regulation of activated PTKs in physiology and disease.

f Yes-associated protein (YAP) is an effector of the Hippo tumor suppressor pathway. The functional significance of YAP in prostate cancer has remained elusive. In this study, we first show that enhanced expression of YAP is able to transform immortalized prostate epithelial cells and promote migration and invasion in both immortalized and cancerous prostate cells. We found that YAP mRNA was upregulated in androgen-insensitive prostate cancer cells (LNCaP-C81 and LNCaP-C4-2 cells) compared to the level in androgen-sensitive LNCaP cells. Importantly, ectopic expression of YAP activated androgen receptor signaling and was sufficient to promote LNCaP cells from an androgen-sensitive state to an androgen-insensitive state in vitro, and YAP conferred castration resistance in vivo. Accordingly, YAP knockdown greatly reduced the rates of migration and invasion of LNCaP-C4-2 cells and under androgen deprivation conditions largely blocked cell division in LNCaP-C4-2 cells. Mechanistically, we found that extracellular signal-regulated kinase-ribosomal s6 kinase signaling was downstream of YAP for cell survival, migration, and invasion in androgen-insensitive cells. Finally, immunohistochemistry showed significant upregulation and hyperactivation of YAP in castration-resistant prostate tumors compared to their levels in hormone-responsive prostate tumors. Together, our results identify YAP to be a novel regulator in prostate cancer cell motility, invasion, and castration-resistant growth and as a potential therapeutic target for metastatic castration-resistant prostate cancer (CRPC). P rostate cancer is the most common malignancy and the second leading cause of cancer-related mortality among men in the United States (1). Although androgen deprivation therapy (through medical or surgical castration) is highly effective for advanced prostate cancer (1, 2), the majority of patients eventually develop resistance and progress to castration-resistant prostate cancer (CRPC). Unfortunately, most cases of CRPC are currently incurable (1). The cause of castration resistance is still not completely known. It is expected that understanding the molecular mechanisms and identifying the molecular pathways underlying the acquisition of castration resistance in prostate cancer are critical for the design of therapeutic strategies and may lead to the discovery of novel targets.The Hippo signaling pathway, originally defined by fly geneticists, plays an important role in tumorigenesis by regulating cell proliferation and apoptosis (3-7). In mammals, protein kinases Mst1/2 (mammalian sterile 20-like 1 and 2) and Lats1/2 (large tumor suppressor 1 and 2) and the adaptor proteins WW45 (WW domain-containing protein) and Mob1 (Mps one binder 1) are the Hippo core components. These proteins form complexes to regulate their activity mainly through phosphorylation. The Hippo core is tumor suppressive and exerts its function by phosphorylating and inactivating YAP (Yes-associated protein) and its paralog, TAZ (transcriptional coactivator with a PDZ-bi...

Misfolding and aggregation of amyloid beta (Aβ)-40 peptide play key roles in the development of Alzheimer's disease (AD). However, very little is known about the molecular mechanisms underlying these molecular processes. We developed a novel experimental approach that can directly probe aggregation-prone states of proteins and their interactions. In this approach, the proteins are anchored to the surface of the AFM substrate (mica) and the probe, and the interaction between anchored molecules is measured in the approach-retraction cycles. We used dynamic force spectroscopy (DFS) to measure the stability of transiently formed dimers. One of the major findings from DFS analysis of α-synuclein (α-Syn) is that dimeric complexes formed by misfolded α-Syn protein are very stable and dissociate over a range of seconds. This differs markedly from the dynamics of monomers, which occurs on a microsecond-nanosecond time scale. Here we applied the same approach to quantitatively characterize interactions of Aβ-40 peptides in a broad range of pH values. These studies showed that misfolded dimers are characterized by the lifetimes in the range of seconds. This value depends on pH and varies between 2.7 s for pH 2.7 and 0.1 s for pH 7, indicating that the aggregation properties of Aβ-40 are modulated by the environmental conditions. The analysis of the contour lengths revealed the existence of various pathways for dimer dissociation, suggesting that dimers with different conformations are formed. These structural variations result in different aggregation pathways, leading to different types of oligomers and higher order aggregates, including fibrils.

The effects on helical stability of weak polar interactions between aromatic side-chains and the peptide backbone were examined. alpha-Helical model peptides, hexa-Ala, with sequential Tyr replacement, were investigated computationally to obtain the geometries and energetics of the interactions. Geometries were obtained with the B3LYP/6-31G* level of theory. Interaction energies were calculated using BHandHLYP/cc-pVTZ and an improved method to correct for basis set superposition error when fragmentation caused steric clashes. Both i, i + 1 and i, i - 4 interactions were observed when Tyr was in position i = 5. The position of the aromatic residue in the amino acid sequence was crucial in facilitating aromatic-backbone interactions. The distance between the center of the aromatic ring of Tyr and the individual interacting backbone atoms ranged from 3.65 to 5.50 A. The interactions have energies of the same order as hydrogen bonds and, thus, could have a significant impact on the stability of the helix.

The tertiary structure of the TC5b miniprotein is stabilized by inter-residue interactions of the Trp-cage, which is composed of a Tyr and several Pro residues surrounding a central Trp residue. The interactions include Ar-Ar (aromatic side-chain-aromatic side-chain), Ar-NH (aromatic side-chain-backbone amide), and CH-pi (aromatic side-chain-aliphatic hydrogen) interactions. In the present work, the strength of the weakly polar interactions found in the TC5b miniprotein was quantified using all of the available 38 NMR structures (1L2Y) from the Protein Data Bank with DFT quantum chemical calculations at the BHandHLYP/cc-pVTZ level of theory and molecular fragmentation with capping of the partial structures. The energies of interaction between the individual residues of the Trp-cage range between -5.85+/-1.41 and -21.30+/-0.88 kcal mol(-1), leading to a significant total structural stabilization energy of -52.13+/-2.56 kcal mol(-1) of which about 50% is from the weakly polar interactions. Furthermore, the strengths of the individual weakly polar interactions are between -2.32+/-0.17 and -2.93+/-0.12 kcal mol(-1) for the CH-pi interactions, between -2.48+/-0.97 and -3.09+/-1.02 kcal mol(-1) for the Ar-NH interaction and -2.74+/-1.06 kcal mol(-1) for the Ar-Ar interaction.