Faculty Bibliography

We compared echovirus 30 strains (FDJS03) which caused an outbreak of aseptic meningitis in China in 2003 with other human enterovirus B strains. Sequencing of the complete genome of FDJS03_84, a representative strain from this outbreak, revealed a mosaic structure with a putative recombination spot within the 2B gene. It was most similar to a strain of the same serotype, E30-14125-00, in the 5' half of the genome but was almost equidistant to all strains analyzed in most of the 3' half of the genome. Phylogenetic relationships in the 5'-untranslated region and the VP1 gene indicated that the FDJS03 isolates were closely related to a distinct lineage of E30 which circulated in countries of the Commonwealth of Independent States during 1999 and 2000. It is most likely that the ancestor of FDJS03 isolates experienced multiple recombination events in the nonstructural protein coding region, which were partly observed in the phylogenetic analysis of the 3D region.

The differentiation potential of T lineage cells becomes restricted soon after entry of multipotent precursors into the thymus and is accompanied by a downregulation of the transcription factors C/EBP alpha and PU.1. To investigate this restriction point, we have expressed C/EBP alpha and PU.1 in fully committed pre-T cells and found that C/EBP alpha (and C/EBP beta) induced the formation of functional macrophages. In contrast, PU.1 converted them into myeloid dendritic cells under identical culture conditions. C/EBP alpha-induced reprogramming is complex because upregulation of some but not all myelomonocytic markers required endogenous PU.1. Notch signaling partially inhibited C/EBP alpha-induced macrophage formation and completely blocked PU.1-induced dendritic cell formation. Likewise, expression of intracellular Notch or the transcription factor GATA-3 inhibited C/EBP alpha-induced lineage conversion. Our data show that committed T cell progenitors remain susceptible to the lineage instructive effects of myeloid transcription factors and suggest that Notch signaling induces T lineage restriction by downregulating C/EBP alpha and PU.1 in multilineage precursors

Vitiligo presents with depigmented cutaneous lesions following localized melanocyte death. Multiple factors contribute to cell death, including genetically determined susceptibility to trauma, and environmental factors, such as exposure to 4-tert-butylphenol (4-TBP). We demonstrate that 4-TBP induces oxidative stress that is more readily overcome by melanocytes from normally pigmented individuals than from two individuals with vitiligo. The antioxidant catalase selectively and significantly reduced death of melanocytes derived from two individuals with vitiligo, indicating a role for oxidative stress in vitiligo pathogenesis. In normal melanocytes, oxidative stress results in reduced expression of microphthalmia-associated transcription factor (MITF). Melanocyte-stimulating hormone-induced expression of MITF protein caused increased sensitivity to 4-TBP, whereas sensitivity of melanomas correlated with MITF expression. MITF stimulates melanin synthesis by up-regulating expression of melanogenic enzymes such as tyrosinase-related protein-1 (Tyrp1). Although melanin content per se did not affect sensitivity to 4-TBP, expression of Tyrp1 significantly increased sensitivity. Melanocytes and melanomas that express functional Tyrp1 were significantly more sensitive to 4-TBP than Tyrp1-null cells. Thus, normal melanocytes respond to 4-TBP by reducing expression of MITF and Tyrp1. We hypothesize that melanocytes in vitiligo demonstrate reduced ability to withstand oxidative stress due, partly, to a disruption in MITF regulation of Tyrp1

The Rag proteins carry out V(D)J recombination through a process mechanistically similar to cut-and-paste transposition. Specifically, Rag complexes form DNA hairpins through direct transesterification, using a catalytic Asp-Asp-Glu (DDE) triad in Rag1. How is sufficient DNA distortion introduced to allow hairpin formation? We hypothesized that, like certain transposases, the Rag proteins might use aromatic amino acid residues to stabilize a flipped-out base. Through in vivo and in vitro experiments and structural predictions, we identified residues in Rag1 crucial for hairpin formation. One of these, a conserved tryptophan (Trp893), probably participates in base-stacking interactions near the cleavage site, as do Trp298, Trp265 and Trp319 in the Tn5, Tn10 and Hermes transposases, respectively. Other residues surrounding the catalytic glutamate (YKEFRK) may share functional similarities with the YREK motif in IS4 family transposases

In this study, using the placental origin theory as a basis, we set out to explore whether hemangioma endothelial cells (HEC) were maternal in origin. We rigorously addressed this hypothesis using several molecular genetic techniques. Fluorescent in situ hybridization on surgical specimens of proliferating hemangiomas (n=8) demonstrated no XX-labeled HEC from resected tumors of male infants. This analysis was followed by PCR genotyping of HEC (n=11) using microsatellite markers where cellular components were genotyped and compared to genomic DNA of corresponding mother-child pairs. In the seven informative mother-child pairs, HEC matched the genotype of the child and not the maternal genotype. Concerned that HEC represented a mixed population of cells, we subsequently enriched for cells using the placental-specific endothelial cell (EC) marker, FcgammaRII. Three informative mother-child pairs exhibited only the genotype of the child in our enriched cell population. Using sequence analysis, we identified an informative single nucleotide polymorphism in an exon of the placental-EC-specific protein, GLUT1. When comparing GLUT1 complementary DNA (cDNA) with mother-child DNA, the genotype of the cDNA matched the constitutional DNA of the child. Our results indicate that hemangiomas are not microchimeric in origin. This study provides further insight into the origin of a tumor whose pathogenesis remains elusive.Journal of Investigative Dermatology (2006) 126, 2533-2538. doi:10.1038/sj.jid.5700516; published online 17 August 2006

Endogenous DC electric fields (EF) are present during embryogenesis and are generated in vivo upon wounding, providing guidance cues for directional cell migration (galvanotaxis) required in these processes. To understand the role of beta (beta)4 integrin in directional migration, the migratory paths of either primary human keratinocytes (NHK), beta4 integrin-null human keratinocytes (beta4-), or those in which beta4 integrin was reexpressed (beta4+), were tracked during exposure to EFs of physiological magnitude (100 mV/mm). Although the expression of beta4 integrin had no effect on the rate of cell movement, it was essential for directional (cathodal) migration in the absence of epidermal growth factor (EGF). The addition of EGF potentiated the directional response, suggesting that at least two distinct but synergistic signaling pathways coordinate galvanotaxis. Expression of either a ligand binding-defective beta4 (beta4+AD) or beta4 with a truncated cytoplasmic tail (beta4+CT) resulted in loss of directionality in the absence of EGF, whereas inhibition of Rac1 blinded the cells to the EF even in the presence of EGF. In summary, both the beta4 integrin ligand-binding and cytoplasmic domains together with EGF were required for the synergistic activation of a Rac-dependent signaling pathway that was essential for keratinocyte directional migration in response to a galvanotactic stimulus

Post-Golgi to apical surface delivery in polarized epithelial cells requires the cytoplasmic dynein motor complex. However, the nature of dynein-cargo interactions and their underlying regulation are largely unknown. Previous studies have shown that the apical surface targeting of rhodopsin requires the dynein light chain, Tctex-1, which binds directly to both dynein intermediate chain (IC) and rhodopsin. In this report, we show that the S82E mutant of Tctex-1, which mimics Tctex-1 phosphorylated at serine 82, has a reduced affinity for dynein IC but not for rhodopsin. Velocity sedimentation experiments further suggest that S82E is not incorporated into the dynein complex. The dominant-negative effect of S82E causes rhodopsin mislocalization in polarized Madin-Darby canine kidney (MDCK) cells. The S82A mutant, which mimics dephosphorylated Tctex-1, can be incorporated into dynein complex but is impaired in its release. Expression of S82A also causes disruption of the apical localization of rhodopsin in MDCK cells. Taken together, these results suggest that the dynein complex disassembles to release cargo due to the specific phosphorylation of Tctex-1 at the S82 residue and that this process is critical for the apical delivery of membrane cargoes.

Apoptosis of terminally differentiated chondrocytes allows the replacement of growth plate cartilage by bone. Despite its importance, little is known about the regulation of chondrocyte apoptosis. We show that overexpression of annexin V, which binds to the cytoplasmic domain of beta5 integrin and protein kinase C alpha (PKCalpha), stimulates apoptotic events in hypertrophic growth plate chondrocytes. To determine whether the balance between the interactions of annexin V/beta5 integrin and annexin V/active PKCalpha play a role in the regulation of terminally differentiated growth plate chondrocyte apoptosis, a peptide mimic of annexin V (Penetratin (Pen)-VVISYSMPD) that binds to beta5 integrin but not to PKCalpha was used. This peptide stimulated apoptotic events in growth plate chondrocytes. Suppression of annexin V expression using small interfering ribonucleic acid decreased caspase-3 activity and increased cell viability in Pen-VVISYSMPD-treated growth plate chondrocytes. An activator of PKC resulted in a further decrease of cell viability and further increase of caspase-3 activity in Pen-VVISYSMPD-treated growth plate chondrocytes, whereas inhibitors of PKCalpha led to an increase of cell viability and decrease of caspase-3 activity of Pen-VVISYSMPD-treated cells. These findings suggest that binding of annexin V to active PKCalpha stimulates apoptotic events in growth plate chondrocytes and that binding of annexin Vto beta5 integrin controls these interactions and ultimately apoptosis