Dynamic expression of two thrombospondins during axolotl limb regeneration.

The molecular processes underlying regeneration remain largely unknown. Several potential factors have been elucidated by focusing on the regenerative function of genes originally identified in a developmental context. A complementary approach is to consider the roles of factors involved in wound healing. Here we focus on the Thrombospondins, a family of secreted extracellular matrix proteins that have been implicated in skin wound healing in mammals. We show that a subset of Thrombospondins are expressed at distinct times and in particular cell types during axolotl limb regeneration. Our studies have revealed the axolotl orthologs of thrombospondin-1 (tsp-1) and thrombospondin-4 (tsp-4) are highly upregulated during limb regeneration in patterns both distinct and similar to larval limb development. Our data suggest that thrombospondins may be key regulators of limb regeneration in axolotl, while their activation appears to be relegated solely to wound healing in vertebrates that have lost the ability to regenerate limbs.

Tubulin tyrosine ligase-like genes ttll3 and ttll6 maintain zebrafish cilia structure and motility.

Tubulin post-translational modifications generate microtubule heterogeneity and modulate microtubule function, and are catalyzed by tubulin tyrosine ligase-like (TTLL) proteins. Using antibodies specific to monoglycylated, polyglycylated, and glutamylated tubulin in whole mount immunostaining of zebrafish embryos, we observed distinct, tissue-specific patterns of tubulin modifications. Tubulin modification patterns in cilia correlated with the expression of ttll3 and ttll6 in ciliated cells. Expression screening of all zebrafish tubulin tyrosine ligase-like genes revealed additional tissue-specific expression of ttll1 in brain neurons, ttll4 in muscle, and ttll7 in otic placodes. Knockdown of ttll3 eliminated cilia tubulin glycylation but had surprisingly mild effects on cilia structure and motility. Similarly, knockdown of ttll6 strongly reduced cilia tubulin glutamylation but only partially affected cilia structure and motility. Combined loss of function of ttll3 and ttll6 caused near complete loss of cilia motility and induced a variety of axonemal ultrastructural defects similar to defects previously observed in zebrafish fleer mutants, which were shown to lack tubulin glutamylation. Consistently, we find that fleer mutants also lack tubulin glycylation. These results indicate that tubulin glycylation and glutamylation have overlapping functions in maintaining cilia structure and motility and that the fleer/dyf-1 TPR protein is required for both types of tubulin post-translational modification.

The apical complex couples cell fate and cell survival to cerebral cortical development.

Cortical development depends upon tightly controlled cell fate and cell survival decisions that generate a functional neuronal population, but the coordination of these two processes is poorly understood. Here we show that conditional removal of a key apical complex protein, Pals1, causes premature withdrawal from the cell cycle, inducing excessive generation of early-born postmitotic neurons followed by surprisingly massive and rapid cell death, leading to the abrogation of virtually the entire cortical structure. Pals1 loss shows exquisite dosage sensitivity, so that heterozygote mutants show an intermediate phenotype on cell fate and cell death. Loss of Pals1 blocks essential cell survival signals, including the mammalian target of rapamycin (mTOR) pathway, while mTORC1 activation partially rescues Pals1 deficiency. These data highlight unexpected roles of the apical complex protein Pals1 in cell survival through interactions with mTOR signaling.

Interactions of ribosomal protein S1 with DsrA and rpoS mRNA.

Ribosomal protein S1 is shown to interact with the non-coding RNA DsrA and with rpoS mRNA. DsrA is a non-coding RNA that is important in controlling expression of the rpoS gene product in Escherichia coli. Photochemical crosslinking, quadrupole-time of flight tandem mass spectrometry, and peptide sequencing have identified an interaction between DsrA and S1 in the 30S ribosomal subunit. Purified S1 binds both DsrA (K(obs) approximately 6 x 10(6) M(-1)) and rpoS mRNA (K(obs) approximately 3 x 10(7) M(-1)). Ribonuclease probing experiments indicate that S1 binding has a weak but detectable effect on the secondary structure of DsrA or rpoS mRNA.

The src-family kinase inhibitor PP2 suppresses the in vitro invasive phenotype of bladder carcinoma cells via modulation of Akt.

OBJECTIVE: To evaluate PP2 as a modulator of the cadherin/catenin complex in late-stage bladder carcinoma cells, and to assess its potential invasion-suppressor activity in this model. MATERIALS AND METHODS: A panel of five human bladder carcinoma cells, characterizing late-stage disease, was used to determine the concentration for 50% inhibition of PP2 in cell-proliferation assays. Modulation of cadherin/catenin expression by PP2 was determined in Western blot analysis, with an assessment of the activation status of mitogen-activated protein kinase and Akt signalling pathways. Altered invasive capacity linked to these variables was determined in standard in vitro invasion assays. RESULTS: PP2 elicited concentration-dependent growth inhibition in all bladder cell lines within the panel, with growth suppression recorded at 10-35 micromol/L PP2. Distinct morphological changes were recorded in cell lines exposed to PP2, accompanied by up-regulation of plakoglobin expression in a subset of lines. Exposure of cells to PP2 resulted in inactivation of Akt in all cells and a concomitant reduction in in vitro invasive capacity. CONCLUSIONS: These results show that PP2 inhibits bladder carcinoma cell growth and can modulate plakoglobin expression in a subset of cell lines. In addition, PP2 can suppress the in vitro invasive capacity of bladder carcinoma cells by modulating the activation status of Akt.

Histone deacetylase inhibitors upregulate plakoglobin expression in bladder carcinoma cells and display antineoplastic activity in vitro and in vivo.

Histone deacetylase inhibitors (HDACis) are emerging as a promising new class of anticancer agents displaying growth-inhibitory activity and low toxicity in vivo. In this study, we examined the effect of sodium butyrate (NaB) and trichostatin A (TSA) on the growth of human bladder carcinoma cell lines in culture and TSA on the growth of EJ and UM-UC-3 human bladder xenografts in nude mice. NaB and TSA suppressed the growth of bladder cell lines at millimolar (1.5-4.3 mM) and micromolar (0.03-0.33 microM) concentrations, respectively, inducing concentration-dependent cell death. Bladder carcinoma cells within the experimental panel displayed the phenotype of late-stage bladder lesions expressing N-cadherin in the absence of E-cadherin accompanied by low levels of plakoglobin expression. Exposure of these cells to HDACis resulted in upregulation of plakoglobin with no change in E-cadherin expression. A 2-hr exposure to TSA was the minimal time required to upregulate plakoglobin in cells with downregulation to baseline levels occurring within 24 hr following drug removal. In mice bearing EJ and UM-UC-3 bladder xenografts, TSA (500 microg/kg/day) caused suppression of tumor growth compared with mice receiving vehicle alone. A > 70% reduction in mean final tumor volume was recorded in both bladder xenograft models with no detectable toxicity. The results suggest that TSA inhibits bladder carcinoma cell growth and may be a useful, relatively nontoxic agent for consideration in the treatment of late-stage bladder tumors.