High Ratio of Early Postoperative Calcitonin to Preoperative Calcitonin Could be a Novel Indicator of Poor Prognosis in Patients with Biochemical Incomplete Responses in Sporadic Medullary Thyroid Cancer.

OBJECTIVE: In a cohort of medullary thyroid cancer (MTC) patients with biochemical incomplete responses, 37 to 48% developed structural persistent disease; however, few indictors were available to distinguish those patients who were more likely to develop structural disease. We hypothesized that the relationship between preoperative calcitonin (Ctn) and postoperative Ctn (within 3 days after surgery) could be used to predict early prognosis of these patients. METHODS: A total of 92 sporadic MTC patients were enrolled in this study. Our team proposed a novel indicator of structural persistent MTC called the calcitonin ratio (CR; CR = postoperative Ctn/preoperative Ctn). Cox regression models and the Kaplan-Meier method were used to evaluate the prognostic capability of CR. The area under the time-dependent receiver-operating characteristic curves (AUC) and the Harrell concordance index (C-index) were used for analysis. RESULTS: The cutoff CR value used to determine MTC prognosis was 0.15. Multivariate Cox analysis revealed that CR (hazard ratio [HR]: 22.974, 95% confidence interval [CI]: 3.259 to 161.959, P = .002), tumor-node-metastasis (HR: 3.968, 95% CI: 1.360 to 21.857; P = .031), and multifocality (HR: 8.466, 95% CI: 1.286 to 55.716; P = .026) independently correlated with MTC prognosis. Kaplan-Meier survival curves demonstrated a lower proportion with structural persistent disease in patients with CR <0.15 (P<.001). The 3, 5, and 10-year AUC values were 0.798, 0.752, and 0.743, respectively. The C-index of CR was 0.788 (95% CI: 0.763 to 0.813). CONCLUSION: In this study, CR was identified as a sensitive and specific risk stratification marker for patients with biochemical incomplete responses in sporadic MTC. ABBREVIATIONS: ATA = American Thyroid Association; AUC = area under curve; CEA = carcinoembryonic antigen; CR = calcitonin ratio; Ctn = calcitonin; HR = hazard ratio; MTC = medullary thyroid cancer; ROC = receiver operating characteristic; TNM = tumor-node-metastasis.

The C-terminus of the oncoprotein TGAT is necessary for plasma membrane association and efficient RhoA-mediated signaling.

BACKGROUND: Rho guanine exchange factors (RhoGEFs) control cellular processes such as migration, adhesion and proliferation. Alternative splicing of the RhoGEF Trio produces TGAT. The RhoGEF TGAT is an oncoprotein with constitutive RhoGEF activity. We investigated whether the subcellular location of TGAT is critical for its RhoGEF activity. METHODS: Since plasma membrane associated RhoGEFs are particularly effective at activating RhoA, plasma membrane localization of TGAT was examined. To this end, we developed a highly sensitive image analysis method to quantitatively measure plasma membrane association. The method requires a cytoplasmic marker and a plasma membrane marker, which are co-imaged with the tagged protein of interest. Linear unmixing is performed to determine the plasma membrane and cytoplasmic component in the fluorescence signal of protein of interest. RESULTS: The analysis revealed that wild-type TGAT is partially co-localized with the plasma membrane. Strikingly, cysteine TGAT-mutants lacking one or more putative palmitoylation sites in the C-tail, still showed membrane association. In contrast, a truncated variant, lacking the last 15 amino acids, TGATΔ15, lost membrane association. We show that membrane localization of TGAT was responsible for high RhoGEF activity by using a RhoA FRET-sensor and by determining F-actin levels. Mutants of TGAT that still maintained membrane association showed similar activity as wild-type TGAT. In contrast, the activity was abrogated for the cytoplasmic TGATΔ15 variant. Synthetic recruitment of TGATΔ15 to membranes confirmed that TGAT effectively activates RhoA at the plasma membrane. CONCLUSION: Together, these results show that membrane association of TGAT is critical for its activity.

A Novel 1,2-Dihydroquinoline Anticancer Agent and Its Delivery to Tumor Cells Using Cationic Liposomes.

AIM: We screened nine 1,2-dihydro-quinolines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay in HepG2 and SMMC cells and identified ethyl-2-cyano-2-(2- (methoxycarbonyl)allyl)quinoline-1(2H)-carboxylate (compound 5) as a potential anticancer agent. In order to further develop its anticancer therapeutic potential, we incorporated this agent into cationic liposomes for delivery to tumor cells. The characteristics of liposomes, their cytotoxicity and cellular uptake by tumor cells were investigated. We demonstrated that cationic 1,2-dioleoyl-3- trimethyl-ammonium-propane containing liposomes (cLips) loaded with compound 5 has superior antitumor activity compared to neutral liposomes. These data suggest cLip-compound 5 to be a promising agent that warrants further evaluation.

Phosphorylation of Dok1 by Abl family kinases inhibits CrkI transforming activity.

The Crk SH2/SH3 adaptor and the Abl nonreceptor tyrosine kinase were first identified as oncoproteins, and both can induce tumorigenesis when overexpressed or mutationally activated. We previously reported the surprising finding that inhibition or knockdown of Abl family kinases enhanced transformation of mouse fibroblasts by CrkI. Abl family inhibitors are currently used or are being tested for treatment of human malignancies, and our finding raised concerns that such inhibitors might actually promote the growth of tumors overexpressing CrkI. Here, we identify the Dok1 adaptor as the key effector for the enhancement of CrkI transformation by Abl inhibition. We show that phosphorylation of tyrosines 295 and 361 of Dok1 by Abl family kinases suppresses CrkI transforming activity, and that upon phosphorylation these tyrosines bind the SH2 domains of the Ras inhibitor p120 RasGAP. Knockdown of RasGAP resulted in a similar enhancement of CrkI transformation, consistent with a critical role for Ras activity. Imaging studies using a FRET sensor of Ras activation revealed alterations in the localization of activated Ras in CrkI-transformed cells. Our results support a model in which Dok1 phosphorylation normally suppresses localized Ras pathway activity in Crk-transformed cells via recruitment and/or activation of RasGAP, and that preventing this negative feedback mechanism by inhibiting Abl family kinases leads to enhanced transformation by Crk.

Functional interplay between type I collagen and cell surface matrix metalloproteinase activity.

Type I collagen stimulation of pro-matrix metalloproteinase (pro-MMP)-2 activation by ovarian cancer cells involves beta(1) integrin receptor clustering; however, the specific cellular and biochemical events that accompany MMP processing are not well characterized. Collagenolysis is not required for stimulation of pro-MMP-2 activation, and denatured collagen does not elicit an MMP-2 activation response. Similarly, DOV13 cells bind to intact collagen utilizing both alpha(2)beta(1) and alpha(3)beta(1) integrins but interact poorly with collagenase-treated or thermally denatured collagen. Antibody-induced clustering of alpha(3)beta(1) strongly promotes activation of pro-MMP-2, whereas alpha(2)beta(1) integrin clustering has only marginal effects. Membrane-type 1 (MT1)-MMP is present on the DOV13 cell surface as both an active 55-kDa TIMP-2-binding species and a stable catalytically inactive 43-kDa form. Integrin clustering stimulates cell surface expression of MT1-MMP and co-localization of the proteinase to aggregated integrin complexes. Furthermore, cell surface proteolysis of the 55-kDa MT1-MMP species occurs in the absence of active MMP-2, suggesting MT1-MMP autolysis. Cellular invasion of type I collagen matrices requires collagenase activity, is blocked by tissue inhibitor of metalloproteinases-2 (TIMP-2) and collagenase-resistant collagen, is unaffected by TIMP-1, and is accompanied by pro-MMP-2 activation. Together, these data indicate that integrin stimulation of MT1-MMP activity is a rate-limiting step for type I collagen invasion and provide a mechanism by which this activity can be down-regulated following collagen clearance.

Type I collagen stabilization of matrix metalloproteinase-2.

The activity of matrix metalloproteinase-2 (MMP-2) is regulated stringently on the posttranslational level. MMP-2 efficiently undergoes autolysis into inactive polypeptides in vitro, prompting the hypothesis that MMP-2 autolysis may function as an alternative mechanism for posttranslational control of MMP-2 in vivo. Moreover, MMP-2 binds to intact type I collagen fibrils; however, the functional consequences of this interaction have not been fully elucidated. To test the hypothesis that MMP-2 binding to type I collagen functions as a positive regulator of MMP-2 proteolytic potential, the effect of type I collagen on MMP-2 activity, inhibition by tissue inhibitor of metalloproteinase-2 (TIMP-2), and enzyme stability was examined. Here, we report that purified MMP-2 binds but does not cleave intact type I collagen. The presence of type I collagen affects neither enzymatic activity against a quenched fluorescent peptide substrate nor the kinetics of inhibition by TIMP-2. However, MMP-2 is stabilized from autolysis in the presence of type I collagen, but not by elastin, fibrinogen, or laminin. These data provide biochemical evidence that MMP-2 exosite interactions with type I collagen may function in the posttranslational control of MMP-2 activity by reducing the rate of autolytic inactivation.

Perturbation of platelet adhesion to endothelial cells by plasminogen activation in vitro.

To investigate whether the endothelium-platelet interactions may be altered by plasminogen activation, cultured human umbilical vein endothelial cells (ECs) were treated with tissue-type plasminogen activator (t-PA) in the presence of plasminogen, and platelet adhesion to ECs was subsequently measured by using a tapered flow chamber. Our results demonstrated that platelets adhered more readily to t-PA treated EC monolayer than to the control monolayer at all shear stress levels tested. This phenomenon was treatment time-dependent and dose-dependent, and it could be blocked by adding plasmin inhibitors, such as epsilon-amino caproic acid and aprotinin. Adherent platelets on t-PA treated EC monolayer underwent more severe shape change than those on the control monolayer. While the extracellular matrix directly treated with t-PA attracted less platelets than the control matrix did, platelet adhesion to the matrix that was produced by t-PA-treated ECs was unaltered. These data suggest that t-PA treatment on ECs compromised antiplatelet-adhesion capability on their apical surface without altering the reactivity of their extracellular matrix towards platelets.

Defining the heparin-binding domain of antithrombin.

Antithrombin is a serine protease inhibitor that participates in the inactivation and removal from the circulation of thrombin and a variety of other procoagulant serine proteases. Antithrombin is also the major plasma cofactor of heparin which exerts its therapeutic effect primarily through its ability to substantially increase the rate of inactivation by antithrombin of the procoagulant serine proteases. Binding of heparin to antithrombin is thus believed to be a prerequisite for this rate enhancement effect. Heparin binding to antithrombin is mediated by a well-defined unique heparin pentasaccharide sequence. Interaction between this pentasaccharide sequence and antithrombin induces a conformational change in antithrombin, an alteration that appears to be sufficient to explain the enhanced ability of antithrombin to inhibit factor Xa and related serine proteases, but not thrombin. Heparin species with longer polysaccharide chains appear to be required in order to enhance the inhibition of thrombin by antithrombin. This may be because the enhancement of this reaction requires that heparin interacts simultaneously with both the antithrombin and the thrombin molecules. This review describes the interactions between heparin and antithrombin, focusing on the antithrombin residues which are involved in the binding of heparin. The role of the heparin-induced conformational change in enhancing serine protease inhibition by antithrombin is also explored. Then, based on available data, an hypothesis is proposed to explain the mechanisms by which heparin accelerates the rate of inactivation by antithrombin of the various serine proteases.