Association of CD99 short and long forms with MHC class I, MHC class II and tetraspanin CD81 and recruitment into immunological synapses

<p>Abstract</p> <p>Background</p> <p>CD99, a leukocyte surface glycoprotein, is broadly expressed in many cell types. On the cell surface, CD99 is expressed as two distinct isoforms, a long form and a short form. CD99 has been demonstrated to play a key role in several biological processes, including the regulation of T cell activation. However, the molecular mechanisms by which CD99 participates in such processes are unclear. As CD99 contains a short cytoplasmic tail, it is unlikely that CD99 itself takes part in its multi-functions. Association of CD99 with other membrane proteins has been suggested to be necessary for exerting its functions.</p> <p>Results</p> <p>In this study, we analyzed the association of CD99 with other cell surface molecules involved in T cell activation. We demonstrate the association of MHC class I, MHC class II and tetraspanin CD81 with CD99 molecules on the cell surface. Association of CD99 with its partners was observed for both isoforms. In addition, we determined that CD99 is a lipid raft-associated membrane protein and is recruited into the immunologic synapse during T cell activation. The implication of CD99 on T cell activation was investigated. Inhibition of anti-CD3 induced T cell proliferation by an anti-CD99 monoclonal antibody was observed.</p> <p>Conclusions</p> <p>We provide evidence that CD99 directly interact and form the complex with the MHC class I and II, and tetraspanin CD81, and is functionally linked to the formation of the immunologic synapse. Upon T cell activation, CD99 engagement can inhibit T cell proliferation. We speculate that the CD99-MHC-CD81 complex is a tetraspanin web that plays an important role in T cell activation.</p

Curcumin-induced HDAC inhibition and attenuation of medulloblastoma growth in vitro and in vivo

<p>Abstract</p> <p>Background</p> <p>Medulloblastoma is the most common brain tumor in children, and its prognosis is worse than for many other common pediatric cancers. Survivors undergoing treatment suffer from serious therapy-related side effects. Thus, it is imperative to identify safer, effective treatments for medulloblastoma. In this study we evaluated the anti-cancer potential of curcumin in medulloblastoma by testing its ability to induce apoptosis and inhibit tumor growth <it>in vitro </it>and <it>in vivo </it>using established medulloblastoma models.</p> <p>Methods</p> <p>Using cultured medulloblastoma cells, tumor xenografts, and the Smo/Smo transgenic medulloblastoma mouse model, the antitumor effects of curcumin were tested <it>in vitro </it>and <it>in vivo</it>.</p> <p>Results</p> <p>Curcumin induced apoptosis and cell cycle arrest at the G2/M phase in medulloblastoma cells. These effects were accompanied by reduced histone deacetylase (HDAC) 4 expression and activity and increased tubulin acetylation, ultimately leading to mitotic catastrophe. In <it>in vivo </it>medulloblastoma xenografts, curcumin reduced tumor growth and significantly increased survival in the Smo/Smo transgenic medulloblastoma mouse model.</p> <p>Conclusions</p> <p>The <it>in vitro </it>and <it>in vivo </it>data suggest that curcumin has the potential to be developed as a therapeutic agent for medulloblastoma.</p

Structural insights into hedgehog ligand sequestration by the human hedgehog-interacting protein HHIP

Hedgehog (Hh) morphogens have fundamental roles in development, whereas dysregulation of Hh signaling leads to disease. Multiple cell-surface receptors are responsible for transducing and/or regulating Hh signals. Among these, the Hedgehog-interacting protein (Hhip) is a highly conserved, vertebrate-specific inhibitor of Hh signaling. We have solved a series of crystal structures for the human HHIP ectodomain and Desert hedgehog (DHH) in isolation, as well as HHIP in complex with DHH (HHIP-DHH) and Sonic hedgehog (Shh) (HHIP-Shh), with and without Ca2+. The interaction determinants, confirmed by biophysical studies and mutagenesis, reveal previously uncharacterized and distinct functions for the Hh Zn2+ and Ca2+ binding sites--functions that may be common to all vertebrate Hh proteins. Zn2+ makes a key contribution to the Hh-HHIP interface, whereas Ca2+ is likely to prevent electrostatic repulsion between the two proteins, suggesting an important modulatory role. This interplay of several metal binding sites suggests a tuneable mechanism for regulation of Hh signaling

GLI activation by atypical protein kinase C ι/λ regulates the growth of basal cell carcinomas

Growth of basal cell carcinomas (BCCs) requires high levels of hedgehog (HH) signalling through the transcription factor GLI. Although inhibitors of membrane protein smoothened (SMO) effectively suppress HH signalling, early tumour resistance illustrates the need for additional downstream targets for therapy. Here we identify atypical protein kinase C ι/λ (aPKC-ι/λ) as a novel GLI regulator in mammals. aPKC-ι/λ and its polarity signalling partners co-localize at the centrosome and form a complex with missing-in-metastasis (MIM), a scaffolding protein that potentiates HH signalling. Genetic or pharmacological loss of aPKC-ι/λ function blocks HH signalling and proliferation of BCC cells. Prkci is a HH target gene that forms a positive feedback loop with GLI and exists at increased levels in BCCs. Genome-wide transcriptional profiling shows that aPKC-ι/λ and SMO control the expression of similar genes in tumour cells. aPKC-ι/λ functions downstream of SMO to phosphorylate and activate GLI1, resulting in maximal DNA binding and transcriptional activation. Activated aPKC-ι/λ is upregulated in SMO-inhibitor-resistant tumours and targeting aPKC-ι/λ suppresses signalling and growth of resistant BCC cell lines. These results demonstrate that aPKC-ι/λ is critical for HH-dependent processes and implicates aPKC-ι/λ as a new, tumour-selective therapeutic target for the treatment of SMO-inhibitor-resistant cancers