PTEN (phosphatase and tensin homologue) is a phosphatase that dephosphorylates both protein and phosphoinositide substrates. It is mutated in a variety of human tumours and has important roles in a diverse range of biological processes, including cell migration and chemotaxis. PTEN's intracellular localization and presumably activity are regulated by chemoattractants in Dictyostelium and mouse neutrophils. However, the mechanisms for its regulation remain elusive. Here we show that RhoA and Cdc42, members of the Rho family of small GTPases, regulate the intracellular localization of PTEN in leukocytes and human transfected embryonic kidney cells. In addition, active RhoA is able to stimulate the phospholipid phosphatase activity of PTEN in human embryonic kidney cells and leukocytes, and this regulation seems to require RhoA's downstream effector, RhoA-associated kinase (Rock). Furthermore, we have identified key residues on PTEN that are required for its regulation by the small GTPase, and show that small GTPase-mediated regulation of PTEN has a significant role in the regulation of chemotaxis.

Edited by Xiao-Fan WangTransforming growth factor-␤ (TGF-␤) signals through both SMAD and non-SMAD pathways to elicit a wide array of biological effects. Existing data have shown the association and coordination between STATs and SMADs in mediating TGF-␤ functions in hepatic cells, but it is not clear how STATs are activated under these circumstances. Here, we report that JAK1 is a constitutive TGF␤RI binding protein and is absolutely required for phosphorylation of STATs in a SMAD-independent manner within minutes of TGF-␤ stimulation. Following the activation of SMADs, TGF-␤ also induces a second phase of STAT phosphorylation that requires SMADs, de novo protein synthesis, and contribution from JAK1. Our global gene expression profiling indicates that the non-SMAD JAK1/STAT pathway is essential for the expression of a subset of TGF-␤ target genes in hepatic stellate cells, and the cooperation between the JAK1-STAT3 and SMAD pathways is critical to the roles of TGF-␤ in liver fibrosis.

TGF-b signalling is regulated by post-translational modifications of Smad proteins to translate quantitative difference in ligand concentration into proportional transcriptional output. Previous studies in cell culture systems suggested that Smad ubiquitination regulatory factors (Smurfs) act in this regulation by targeting Smads for proteasomal degradation, but whether this mechanism operates under physiological conditions is not clear. Here, we generated mice harbouring a target-disrupted Smurf2 allele. Using primary mouse embryonic fibroblasts and dermal fibroblasts, we show that TGF-b-mediated, Smaddependent transcriptional responses are elevated in the absence of Smurf2. Instead of promoting poly-ubiquitination and degradation, we show that Smurf2 actually induces multiple mono-ubiquitination of Smad3 in vivo. Phosphorylation of T179, immediately upstream of the Smad3 PY motif, enhances Smurf2 and Smad3 interaction and Smad3 ubiquitination. We have mapped Smurf2-induced Smad3 ubiquitination sites to lysine residues at the MH2 domain, and demonstrate that Smad3 ubiquitination inhibits the formation of Smad3 complexes. Thus, our data support a model in which Smurf2 negatively regulates TGFb signalling by attenuating the activity of Smad3 rather than promoting its degradation.

Cell surface reception of Sonic hedgehog (Shh) must ensure that the graded morphogenic signal is interpreted accordingly in neighboring cells to specify tissue patterns during development. Here, we report endocytic sorting signals for the receptor Patched1 (Ptch1), comprising two ‘PPXY’ motifs, that direct it to degradation in lysosomes. These signals are recognized by two HECT-domain ubiquitin E3 ligases, Smurf1 and Smurf2, which are induced by Shh and become enriched in Caveolin-1 lipid rafts in association with Ptch1. Smurf-mediated endocytic turnover of Ptch1 is essential for its clearance from the primary cilium and pathway activation. Removal of both Smurfs completely abolishes the ability of Shh to sustain the proliferation of postnatal granule cell precursors in the cerebellum. These findings reveal a novel step in the Shh pathway activation as part of the Ptch1 negative feedback loop that precisely controls the signaling output in response to Shh gradient signal.DOI: http://dx.doi.org/10.7554/eLife.02555.001

We present the first proteomic analysis on the cellular response to severe acute respiratory syndrome-associated coronavirus (SARS-CoV) infection. The differential proteomes of Vero E6 cells with and without infection of the SARS-CoV were resolved and quantitated with twodimensional differential gel electrophoresis followed by ESI-MS/MS identification. Moreover isotope-coded affinity tag technology coupled with two-dimensional LC-MS/MS were also applied to the differential proteins of infected cells. By combining these two complementary strategies, 355 unique proteins were identified and quantitated with 186 of them differentially expressed (at least 1.5-fold quantitative alteration) between infected and uninfected Vero E6 cells. The implication for cellular responses to virus infection was analyzed in depth according to the proteomic results. Thus, the present work provides large scale protein-related information to investigate the mechanism of SARS-CoV infection and pathogenesis. Molecular & Cellular Proteomics 4:902-913, 2005.A new type of coronavirus was reported as the causal agent of severe acute respiratory syndrome (SARS) 1 in April 2003, and the genome of the SARS-CoV was sequenced by several groups (1-3). The properties of the SARS-CoV genome was analyzed in depth by bioinformatic tools (4, 5). In addition, several important works on the proteins of SARS-CoV have been reported recently, including the identification of SARSCoV 3C-like protease structure (6) and the identification of angiotensin-converting enzyme 2 as a functional receptor for the spike protein (7). In our recent work, we identified all of the predicted SARS-CoV structural proteins, nucleocapsid (N), membrane (M), spike (S), and envelope (E), using proteomic approaches and found a novel protein, SARS-CoV 3a (8, 9).To uncover the mechanisms of cellular responses to the virus infection and identify potential drug targets of antiviral treatment, it is very useful to study the molecular profiling of virus-infected cells with high throughput and quantitative approaches. Analysis of gene expression profiles during viral infection is one of the powerful approaches to probe potential cellular genes involved in viral infection and pathogenesis (10). The recent development of proteomic analytic technology such as differential gel electrophoresis (DIGE) (11, 12) and ICAT (13, 14) also provides new tools for such studies.As a method based on two-dimensional (2D) electrophoresis, DIGE allows two or three independent samples labeled with different fluorescent dyes such as cyanine-2 (Cy2), cyanine-3 (Cy3), and cyanine-5 (Cy5) to be run in one gel simultaneously and viewed individually using the different fluorescent properties of Cy2, Cy3, and Cy5, circumventing some of the reproducibility problems associated with 2D electrophoresis and providing more accurate quantitative information compared with other staining methods such as silver staining with the dynamic range over 3-4 orders of magnitude (11,12). More recently, the combination of stable ICAT, L...

Non-Small Cell Lung Cancer (NSCLC) is a common malignancy and leading cause of death by cancer. Metastasis and drug resistance are serious clinical problems encountered in NSCLC therapy. Aberrant activation of the Transforming Growth Factor beta (TGFβ) and Hedgehog (Hh) signal transduction cascades often associate with poor prognosis and aggressive disease progression in NSCLC, as these signals can drive cell proliferation, angiogenesis, metastasis, immune evasion and emergence of drug resistance. Therefore, simultaneous inhibition of TGFβ and Hh signaling, by a single agent, or in combination with other drugs, could yield therapeutic benefits in NSCLC and other cancers. In the current study, we report on the biological and pharmacological evaluation of Oxy210, an oxysterol-based dual inhibitor of TGFβ and Hh signaling. In NSCLC cells, Oxy210 inhibits proliferation, epithelial-mesenchymal transition (EMT) and invasive activity. Combining Oxy210 with Carboplatin (CP) increases the anti-proliferative response to CP and inhibits TGFβ-induced resistance to CP in A549 NSCLC cells. In addition, Oxy210 displays encouraging drug-like properties, including chemical scalability, metabolic stability and oral bioavailability in mice. Unlike other known inhibitors, Oxy210 antagonizes TGFβ and Hh signaling independently of TGFβ receptor kinase inhibition and downstream of Smoothened, respectively.

Promoting the degradation of Hsp90 client proteins by inhibiting Hsp90, an important protein chaperone, has been shown to be a promising new anticancer strategy. In this study, we show that an oxazoline analogue of apratoxin A (oz-apraA), a cyclodepsipeptide isolated from a marine cyanobacterium, promotes the degradation of Hsp90 clients through chaperone-mediated autophagy (CMA). We identify a KFERQ-like motif as a conserved pentapeptide sequence in the kinase domain of epidermal growth factor receptor (EGFR) necessary for recognition as a CMA substrate. Mutation of this motif prevents EGFR degradation by CMA and promotes the degradation of EGFR through the proteasomal pathway in oz-apraA–treated cells. Oz-apraA binds to Hsc70/Hsp70. We propose that apratoxin A inhibits Hsp90 function by stabilizing the interaction of Hsp90 client proteins with Hsc70/Hsp70 and thus prevents their interactions with Hsp90. Our study provides the first examples for the ability of CMA to mediate degradation of membrane receptors and cross talks of CMA and proteasomal degradation mechanisms.

Background: Ubiquitin E3 ligase Smurf1 plays an important role in cell migration and tumor metastasis. Results: Smurf1 ubiquitinates TRAF4 at K190, which is required for TRAF4 localization at the cell junction. It also promotes cell migration and activates Rac1. Conclusion: Smurf1 regulates cell migration through ubiquitination of TRAF4. Significance: TRAF4 ubiquitination is a key regulatory step in controlling breast epithelial and cancer cell migration.