Exogenous expression of synaptotagmin XIII suppresses the neoplastic phenotype of a rat liver tumor cell line through molecular pathways related to mesenchymal to epithelial transition.

The molecular pathogenesis of hepatocellular carcinoma is well-studied but not completely understood. We utilized a microcell-hybrid model of tumor suppression in rat liver tumor cells to facilitate the identification of liver tumor suppressor genes located on human chromosome 11. These investigations confirmed a liver tumor suppressor locus at human 11p11.2, identified Wt1 as a potential effector of 11p11.2-mediated tumor suppression, and subsequently identified human SYT13 as a strong candidate for the 11p11.2 liver tumor suppressor gene. In the studies presented here, we introduced SYT13 into the GN6TF rat liver tumor cell line to characterize a functional role for SYT13 in this model system. Transfected clones expressing an SDS-resistant dimer form of the SYT13 protein displayed induction of Wt1 gene expression and a significant attenuation of the neoplastic phenotype exhibited by the parental tumor cell line. Saturation densities and anchorage-independent growth of SYT13 dimer-positive cell lines were reduced in vitro, and tumorigenicity was significantly decreased or ablated in syngeneic host rats in vivo. In addition, restoration of the contact-inhibited, epithelioid morphology observed in normal liver epithelial cells accompanied ectopic expression of the SYT13 protein dimer, suggesting that SYT13 may be mediating an epithelial differentiation coordinate with tumor suppression in these cells. Accordingly, the expression of E-cadherin (Cdh1) mRNA was increased >100-fold in SYT13-dimer-positive cell lines and the Cdh1 transcriptional repressor Snail was decreased >3-fold in these cells compared to the parental tumor cells. These studies combine to suggest that SYT13 is a liver tumor suppressor gene and that its function may be mediated through pathways implicated in mesenchymal to epithelial transition.

Re-expression of tumorigenicity after attenuation of human synaptotagmin 13 in a suppressed microcell hybrid cell line.

Human chromosome 11p11.2 contains a putative liver tumor suppressor locus that was identified using a microcell hybrid cell line-based model of tumor suppression. Transcription mapping of suppressed microcell hybrid cell lines suggests that human SYT13 represents a strong candidate for the 11p11.2 tumor suppressor gene. Other evidence suggests that the putative 11p11.2 tumor suppressor gene (SYT13 or some other) may modulate the tumorigenic potential of neoplastic liver cell lines through direct or indirect regulation of the rat Wt1 tumor suppressor gene. To characterize a functional role for SYT13 in liver tumor suppression, we employed RNAi to attenuate SYT13 expression in a suppressed microcell hybrid cell line (GN6TF-11neoCX4). SYT13-attenuated cells display aggressive phenotypic properties that are similar to or indistinguishable from the parental tumor cells (GN6TF), including altered cellular morphologies, disrupted contact inhibition, elevated saturation densities, restoration of anchorage-independent growth and increased tumorigenicity in vivo. Moreover, SYT13 attenuation and re-expression of tumorigenicity in GN6TF-11neoCX4-derived cell lines was accompanied by a significant decrease of Wt1 expression. In contrast, the phenotypic properties of scrambled-control cells were similar to the suppressed microcell hybrid cells and Wt1 expression was unaffected. These observations combine to establish that: i) human SYT13 functions as a liver tumor suppressor gene that complements a molecular defect in GN6TF rat liver tumor cells resulting in a normalized cellular phenotype in vitro and suppression of tumorigenicity in vivo; ii) RNAi-mediated attenuation of SYT13 expression restores the neoplastic phenotype of GN6TF-11neoCX4 microcell hybrid cells, consistent with the function of a liver tumor suppressor gene; and iii) loss of Wt1 expression is important for the re-establishment of tumorigenic potential by GN6TF-11neoCX4 microcell hybrid cells after attenuation of SYT13.

Proteinase 3 sidesteps caspases and cleaves p21(Waf1/Cip1/Sdi1) to induce endothelial cell apoptosis.

BACKGROUND: Emerging data raise possibilities of a complex and specific biologic role for leukocyte-derived proteases in substrate processing and in signaling pathways. Neutrophil proteinase 3 (PR3) is a caspase-like protease that enters endothelial cells, cleaves nuclear factor-kappaB (NF-kappaB), and induces sustained JNK activation, implying that the major cell cycle inhibitor p21 may be inactivated. Cleavage of p21 by caspase-3 is reported to be required for endothelial cell apoptosis. We hypothesized that PR3 may target p21. METHODS: Human umbilical vein endothelial cells (HUVEC) were treated with or without PR3 (5 microg/mL) from 0 hours or up to 8 hours, and analyzed for changes in cell cycle control proteins by immunoblotting, immunofluorescence and flow cytometry. RESULTS: PR3 exposure resulted in cleavage of p21 between Thr80 and Gly81, loss of nuclear p21 by cytoplasmic sequestration and depletion of p21 from cyclin/cyclin-dependent kinase (CDK) complexes. Examination of cyclins D and E, p53, Rb, and p27 revealed a largely nonproliferative expression profile. Cells arrested in G1 were more susceptible to PR3 effects. We examined inflamed human colonic tissue and found a fragment similar in size to that generated by PR3 in HUVEC. Granzyme B, a T-cell homologue of PR3 that cleaves caspase substrates, also cleaves p21 between Asp62 and Phe63. A reported substrate of granzyme B and caspases, Bid, is cleaved by PR3 signifying commonality of substrates among these proteases. CONCLUSION: A theme is developing that the granulocyte protease, PR3, is an exogenous caspase-like molecule that can sidestep intracellular caspase functions at sites of inflammation.

Identification of candidate liver tumor suppressor genes from human 11p11.2 by transcription mapping of microcell hybrid cell lines.

Our previous studies utilized a microcell hybrid (MCH) cell line-based functional model of tumor suppression to localize a liver tumor suppressor to human chromosome 11, map the suppressor locus to a <1-Mb region within human 11p11.2, and identify a number of expressed sequence tags (ESTs) and genes that represent candidate liver tumor suppressor genes. The Human Genome Project has recently positioned a number of additional genes, ESTs, and predicted genes within the human 11p11.2 liver tumor suppressor region. In this study, we analyzed 26 ESTs and genes (known and predicted) that have been localized to human 11p11.2. Four of these ESTs/genes (FLJ23598, FLJ10450, KIAA1580, SYT13) mapped to the minimal tumor suppressor region of human 11p11.2, the smallest region conferring suppression of tumorigenicity in the MCH cell lines. Each of these ESTs/genes were expressed among an index panel of suppressed MCH cell lines (derived from GN6TF rat liver tumor cells), suggesting that these ESTs/genes represent excellent candidates for the human 11p11.2 liver tumor suppressor gene. To verify the candidate status of these sequences, 8 additional MCH cell lines (derived from GN3TG and GP10TA rat liver tumor cells) were analyzed. Three ESTs/genes (FLJ23598, FLJ10450, KIAA1580) proved to be less than ideal candidates, based upon their loss from suppressed MCH cell lines (DNA deletion), and/or their retention and expression in a non-suppressed MCH cell line. In contrast, SYT13 is present in the DNA from all suppressed MCH cell lines (n=10), and is deleted in a non-suppressed MCH cell line. Furthermore, SYT13 mRNA is expressed in 100% of suppressed cell lines, and is not expressed in the non-suppressed MCH cell line or in MCH-derived tumor cell lines (n=6). These results suggest that SYT13 is an excellent candidate for the human 11p11.2 liver tumor suppressor gene based upon its: i) location within the human 11p11.2 liver tumor suppressor region; ii) loss from the DNA of a non-suppressed MCH cell line that lacks the human 11p11.2 liver tumor suppressor region; iii) expression among suppressed MCH cell lines; and iv) lack of expression by MCH-derived tumor cell lines.