Myriam Roussigne

Molecular Characterization of NF-HEV, a Nuclear Factor Preferentially Expressed in Human High Endothelial Venules

Lymphocyte homing to secondary lymphoid tissue and lesions of chronic inflammation is directed by multi-step interactions between the circulating cells and the specialized endothelium of high endothelial venules (HEVs). In this study, we used the PCR-based method of suppression subtractive hybridization (SSH) to identify novel HEV genes by comparing freshly purified HEV endothelial cells (HEVECs) with nasal polyp-derived microvascular endothelial cells (PMECs). By this approach, we cloned the first nuclear factor preferentially expressed in HEVECs, designated nuclear factor from HEVs (NF-HEV). Virtual Northern and Western blot analyses showed strong expression of NF-HEV in HEVECs, compared to human umbilical vein endothelial cells (HUVECs) and PMECs. In situ hybridization and immunohistochemistry revealed that NF-HEV mRNA and protein are expressed at high levels and rather selectively by HEVECs in human tonsils, Peyerss patches, and lymph nodes. The NF-HEV protein was found to contain a bipartite nuclear localization signal, and was targeted to the nucleus when ectopically expressed in HUVECs and HeLa cells. Furthermore, endogenous NF-HEV was found in situ to be confined to the nucleus of tonsillar HEVECs. Finally, threading and molecular modeling studies suggested that the amino-terminal part of NF-HEV (aa 1-60) corresponds to a novel homeodomain-like Helix-Turn-Helix (HTH) DNA-binding domain. Similarly to the atypical homeodomain transcription factor Prox-1, which plays a critical role in the induction of the lymphatic endothelium phenotype, NF-HEV may be one of the key nuclear factors that controls the specialized HEV phenotype.

THAP1 is a nuclear proapoptotic factor that links prostate-apoptosis-response-4 (Par-4) to PML nuclear bodies

Promyelocytic leukemia (PML) nuclear bodies (PML NBs) are discrete subnuclear domains organized by the promyelocytic leukemia protein PML, a tumor suppressor essential for multiple apoptotic pathways. We have recently described a novel family of cellular factors, the THAP proteins, characterized by the presence at their amino-terminus of an evolutionary conserved putative DNA-binding motif, designated THAP domain. Here, we report that THAP1 is a novel nuclear proapoptotic factor associated with PML NBs, which potentiates both serum withdrawal- and TNFα-induced apoptosis, and interacts with prostate-apoptosis-response-4 (Par-4), a well characterized proapoptotic factor, previously linked to prostate cancer and neurodegenerative diseases. We show that endogenous Par-4 colocalizes with ectopic THAP1 within PML NBs in primary endothelial cells and fibroblasts. In addition, we found that Par-4 is a component of PML NBs in blood vessels, a major site of PML expression in vivo. Finally, we investigated the role of the THAP domain in THAP1 activities and found that this putative DNA-binding domain is not required for Par-4 binding and localization within PML NBs, but is essential for THAP1 proapoptotic activity. Together, our results provide an unexpected link between a nuclear factor of the THAP family, the proapoptotic protein Par-4 and PML nuclear bodies.

The THAP domain: a novel protein motif with similarity to the DNA-binding domain of P element transposase

We have identified a novel evolutionarily conserved protein motif - designated the THAP domain - that defines a new family of cellular factors. We have found that the THAP domain presents striking similarities with the site-specific DNA-binding domain (DBD) of Drosophila P element transposase, including a similar size, N-terminal location, and conservation of the residues that define the THAP motif, such as the C2CH signature (Cys-Xaa(2-4)-Cys-Xaa(35-50)-Cys-Xaa(2)-His). Our results suggest that the THAP domain is a novel example of a DBD that is shared between cellular proteins and transposases from mobile genomic parasites.

Chemotrap-1: an engineered soluble receptor that blocks chemokine-induced migration of metastatic cancer cells in vivo.

Cancer and dendritic cells recognize and migrate toward chemokines secreted from lymphatics and use this mechanism to invade the lymphatic system, and cancer cells metastasize through it. The lymphatic-secreted chemokine ligand CCL21 has been identified as a key regulatory molecule in the switch to a metastatic phenotype in melanoma and breast cancer cells. However, it is not known whether CCL21 inhibition is a potential therapeutic strategy for inhibition of metastasis. Here, we describe an engineered CCL21-soluble inhibitor, Chemotrap-1, which inhibits migration of metastatic melanoma cells in vivo. Two-hybrid, pull-down, and coimmunoprecipitation assays allowed us to identify a naturally occurring human zinc finger protein with CCL21 chemokine-binding properties. Further analyses revealed a short peptide (∼70 amino acids), with a predicted coiled-coil structure, which is sufficient for association with CCL21. This CCL21 chemokine-binding peptide was then fused to the Fc region of human IgG1 to generate Chemotrap-1, a human chemokine-binding Fc fusion protein. Surface plasmon resonance and chemotaxis assays showed that Chemotrap-1 binds CCL21 and inhibits CCL21-induced migration of melanoma cells in vitro with subnanomolar affinity. In addition, Chemotrap-1 blocked migration of melanoma cells toward lymphatic endothelial cells in vitro and in vivo. Finally, Chemotrap-1 strongly reduced lymphatic invasion, tracking, and metastasis of CCR7-expressing melanoma cells in vivo. Together, these results show that CCL21 chemokine inhibition by Chemotrap-1 is a potential therapeutic strategy for metastasis and provide further support for the hypothesis that lymphatic-mediated metastasis is a chemokine-dependent process.