KLF4 and CD55 expression and function depend on each other.

The transcription factor Kruppel-like factor 4 (KLF4) regulates the expression of immunosuppressive and anti-thrombotic proteins. Despite its importance in maintaining homeostasis, the signals that control its expression and the mechanism of its transactivation remain unclarified. CD55 [aka decay accelerating factor (DAF)], now known to be a regulator of T and B cell responses, biases between pro- and anti-inflammatory processes by controlling autocrine C3a and C5a receptor (C3ar1/C5ar1) signaling in cells. The similarity in CD55's and KLF4's regulatory effects prompted analyses of their functional relationship. In vascular endothelial cells (ECs), CD55 upregulation accompanied KLF4 expression via a p-CREB and CREB Binding Protein (CBP) mechanism. In both ECs and macrophages, CD55 expression was essential for KLF4's downregulation of pro-inflammatory/pro-coagulant proteins and upregulation of homeostatic proteins. Mechanistic studies showed that upregulation of KLF4 upregulated CD55. The upregulated CD55 in turn enabled the recruitment of p-CREB and CBP to KLF4 needed for its transcription. Activation of adenylyl cyclase resulting from repression of autocrine C3ar1/C5ar1 signaling by upregulated CD55 concurrently led to p-CREB and CBP recruitment to KLF4-regulated genes, thereby conferring KLF4's transactivation. Accordingly, silencing CD55 in statin-treated HUVEC disabled CBP transfer from the E-selectin to the eNOS promoter. Importantly, silencing CD55 downregulated KLF4's expression. It did the same in untreated HUVEC transitioning from KLF4low growth to KLF4hi contact inhibition. KLF4's and CD55's function in ECs and macrophages thus are linked via a novel mechanism of gene transactivation. Because the two proteins are co-expressed in many cell types, CD55's activity may be broadly tied to KLF4's immunosuppressive and antithrombotic activities.

A novel role for CD55 in granulocyte homeostasis and anti-bacterial host defense.

BACKGROUND: In addition to its complement-regulating activity, CD55 is a ligand of the adhesion class G protein-coupled receptor CD97; however, the relevance of this interaction has remained elusive. We previously showed that mice lacking a functional CD97 gene have increased numbers of granulocytes. METHODOLOGY/RESULTS: Here, we demonstrate that CD55-deficient mice display a comparable phenotype with about two-fold more circulating granulocytes in the blood stream, the marginated pool, and the spleen. This granulocytosis was independent of increased complement activity. Augmented numbers of Gr-1-positive cells in cell cycle in the bone marrow indicated a higher granulopoietic activity in mice lacking either CD55 or CD97. Concomitant with the increase in blood granulocyte numbers, Cd55⁻/⁻ mice challenged with the respiratory pathogen Streptococcus pneumoniae developed less bacteremia and died later after infection. CONCLUSIONS: Collectively, these data suggest that complement-independent interaction of CD55 with CD97 is functionally relevant and involved in granulocyte homeostasis and host defense.

Long-term-infected telomerase-immortalized endothelial cells: a model for Kaposi's sarcoma-associated herpesvirus latency in vitro and in vivo.

Kaposi's sarcoma-associated herpesvirus (KSHV) is associated with Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease. Most KS tumor cells are latently infected with KSHV and are of endothelial origin. While PEL-derived cell lines maintain KSHV indefinitely, all KS tumor-derived cells to date have lost viral genomes upon ex vivo cultivation. To study KSHV latency and tumorigenesis in endothelial cells, we generated telomerase-immortalized human umbilical vein endothelial (TIVE) cells. TIVE cells express all KSHV latent genes 48 h postinfection, and productive lytic replication could be induced by RTA/Orf50. Similar to prior models, infected cultures gradually lost viral episomes. However, we also obtained, for the first time, two endothelial cell lines in which KSHV episomes were maintained indefinitely in the absence of selection. Long-term KSHV maintenance correlated with loss of reactivation in response to RTA/Orf50 and complete oncogenic transformation. Long-term-infected TIVE cells (LTC) grew in soft agar and proliferated under reduced-serum conditions. LTC, but not parental TIVE cells, formed tumors in nude mice. These tumors expressed high levels of the latency-associated nuclear antigen (LANA) and expressed lymphatic endothelial specific antigens as found in KS (LYVE-1). Furthermore, host genes, like those encoding interleukin 6, vascular endothelial growth factor, and basic fibroblast growth factor, known to be highly expressed in KS lesions were also induced in LTC-derived tumors. KSHV-infected LTCs represent the first xenograft model for KS and should be of use to study KS pathogenesis and for the validation of anti-KS drug candidates.

The latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus modulates cellular gene expression and protects lymphoid cells from p16 INK4A-induced cell cycle arrest.

Latently infected Kaposi's sarcoma-associated herpes-virus (KSHV)-associated tumor cells have both endothelial and lymphoid origins and express a limited set of latent viral genes. One such gene, ORF73, encodes the latency-associated nuclear antigen (LANA), a multifunctional protein that plays roles in viral DNA replication, episome maintenance, and transcriptional regulation. LANA interacts with cellular proteins involved in transcriptional regulation such as the tumor suppressors, retinoblastoma (Rb) and p53, and RING3 family members. Although several reports about specific LANA-regulated promoters exist, only limited data are available that address how LANA expression in KSHV-infected cells globally affects cellular gene expression, thereby potentially contributing to KSHV pathogenicity. To investigate this question, we generated an Epstein-Barr virus-negative Burkitts lymphoma line that expresses LANA from a tetracycline-inducible promoter (BJAB/Tet-On/LANA), and we performed microarray-based gene expression profiling. Expression profiling at different time points post-induction revealed that 186 genes were activated or repressed over 2-fold in the presence of LANA. Of these genes, 41 are regulated in the Rb/E2F pathway, whereas 7 are related to p53 signaling. To determine whether these gene expression changes translate into LANA-dependent changes in cell cycle regulation, we overexpressed p16 INK4a, a CDK4/6 inhibitor that efficiently induces cell cycle arrest in Rb-positive cells. Under these conditions, LANA expression protects lymphoid cells from p16 INK4a-induced cell cycle arrest and induces S-phase entry.

c-Met expression in gastric cancer with liver metastasis.

Liver metastasis is one of the poor prognostic factors for gastric cancer. Hepatocyte growth factor (HGF) and its receptor, c-Met, have been reported to be related to the proliferation of carcinoma cells. We examined c-Met and HGF expression in stage IV gastric cancers (n = 121) and compared the results in groups with liver metastasis (n = 47, LM group) and without liver metastasis (n = 74, no-LM group). The survival rate for the LM group was significantly poorer than for the no-LM group (p < 0.01). We found a high frequency of c-Met expression in the LM group compared with the no-LM group at protein level detected by immunohistochemistry (p = 0.0005) and at mRNA level detected by semiquantitative reverse transcriptase-polymerase chain reaction (p = 0.0386) in primary gastric tumors. Furthermore, we evaluated HGF expression in both carcinoma cells and stromal cells in gastric cancers. There was no significant difference in the HGF expression between the LM and no-LM groups. The labeling index of proliferating cell nuclear antigen for the carcinomas in the LM group was higher than that in the no-LM group (47.1 +/- 24.5 vs. 26.2 +/- 24.5%, p < 0.0001). Thus, the high frequency of c-Met overexpression in carcinoma cells may be involved in the mechanism of liver metastasis in gastric cancers. Moreover, the evaluation of c-Met expression might be a useful indicator of liver metastasis in patients with gastric cancer.