Downstream targets of Nm23-H1: gene expression profiling of CAL 27 cells using DNA microarray

NM23/NDPK proteins in transcription regulatory functions and chromatin modulation: emerging trends

NM23/NDPK proteins have been studied for their metastasis suppressor role but the molecular pathways involved in this process are not very vivid. Nucleotide binding and kinase activities of NM23 proteins implicated in anti-metastatic effects have been widely studied. In addition to these, transcriptional regulation adds another arm to the versatility of NM23 proteins that together with the other functions may contribute to better understanding of underlying mechanisms. In this review we discuss emerging reports describing the role of NM23 proteins in gene regulation and chromatin modulation in association with other factors or on their own.

Nm23-H1 can induce cell cycle arrest and apoptosis in B cells

Nm23-H1 is a well-known tumor metastasis suppressor, which functions as a nucleoside-diphosphate kinase converting nucleoside diphosphates to nucleoside triphosphates with an expense of ATP. It regulates a variety of cellular activities, including proliferation, development, migration and differentiation known to be modulated by a series of complex signaling pathway. Few studies have addressed the mechanistic action of Nm23-H1 in the context of these cellular processes. To determine the downstream pathways modulated by Nm23-H1, we expressed Nm23-H1 in a Burkitt lymphoma derived B-cell line BJAB and performed pathway specific microarray analysis. The genes with significant changes in expression patterns were clustered in groups which are responsible for regulating cell cycle, p53 activities and apoptosis. We found a general reduction of cell cycle regulatory proteins including cyclins and cyclin dependent kinase inhibitors (anti proliferation), and upregulation of apoptotic genes which included caspase 3, 9 and Bcl-x. Nm23-H1 was also found to upregulate p53 and downregulate p21 expression. A number of these genes were validated by real time PCR and results from promoter assays indicated that Nm23-H1 expression downregulated cyclin D1 in a dose responsive manner. Further, we show that Nm23-H1 forms a complex with the cellular transcription factor AP1 to modulate cyclin D1 expression levels. BJAB cells expressing Nm23-H1 showed reduced proliferation rate and were susceptible to increased apoptosis which may in part be due to a direct interaction between Nm23-H1 and p53. These results suggest that Nm23-H1 may have a role in the regulation of cell cycle and apoptosis in human B-cells.

Nm23-H1 promotes adhesion of CAL 27 cells in vitro

nm23-H1 was found to diminish metastatic potential of carcinoma cell lines and therefore was placed in the group of metastatic suppressor genes. Its protein product has a function of a nucleoside diphosphate kinase (NDPK) as well as protein kinase and nuclease. Though it was found that Nm23-H1 is involved in many cellular processes, it is still not known how it promotes metastatic suppressor activity. Since the process of metastasis is dependent on adhesion properties of cells, the goal of our work was to describe the adhesion properties of CAL 27 cells (oral squamous cell carcinoma of the tongue) overexpressing FLAG/nm23-H1. In our experiments, cells overexpressing nm23-H1 show reduced migratory and invasive potential. Additionally, cells overexpressing nm23-H1 adhere stronger on substrates (collagen IV and fibronectin) and show more spread morphology than the control cells. Results obtained by EGF induction of migration revealed that the adhesion strength predetermined cell response to chemoattractant and that Nm23-H1, in this cell type, does not interfere with, EGF induced, Ras signaling pathway. These data contribute to the overall knowledge about nm23-H1 and its role in cell adhesion, migration, and invasion, especially in oral squamous cell carcinoma.

Altered gene and protein expression by Nm23-H1 in metastasis suppression

Metastasis suppressor genes (MSG) are characterized by their ability to inhibit the formation of metastasis, while not affecting the growth of the primary tumor in vivo. Nm23-H1, the first MSG to be characterized, has been shown to alter both gene and protein expression in cancer cells. Recently, microarray expression profiling revealed that Nm23-H1 downregulated EDG2, which encodes for a lysophosphatidic acid (LPA) receptor. Reintroduction of EDG2 into cells that express Nm23-H1 overcame the metastasis suppressive ability of Nm23-H1 in both in vivo pulmonary colonization and spontaneous metastasis assays. In addition, isotope capture affinity tag (ICAT) proteomic analysis was performed to identify differentially expressed proteins not accounted for by microarray analysis. ICAT identified several differentially regulated proteins, including GEMIN5, a protein involved in differential mRNA splicing. The contribution of alternative mRNA splicing to cancer and cancer metastasis is poorly defined. It is possible that Nm23-H1, through the regulation of RNA processing proteins, may play a role in proteome stability.

Nm23-H1 is responsible for SUMO-2-involved DNA synthesis induction after X-ray irradiation in human cells

Human cells derived from nevoid basal carcinoma syndrome (NBCCS) patients show increased levels of DNA synthesis activity after X-ray irradiation which is suggested to be casually related to reduction in cellular amounts of small ubiquitin-like protein modifier (SUMO-2/SMT-3A). In the present study, an increased level of DNA synthesis activity was found 8h after X-ray irradiation in HeLa cells with reduction in SUMO-2 amounts by siRNA treatment for SUMO-2. When comparative proteomic analysis was performed between the siRNA and mimic control siRNA treated cells using two-dimensional (2D) electrophoresis and mass spectrometry, three proteins were identified as candidates. Our research focused on Nm23-H1, a nucleoside diphosphate kinase, whose amounts decreased after X-ray irradiation in HeLa cells treated with siRNA for SUMO-2. In the Nm23-H1 siRNA treated cells, induction of DNA synthesis was also detected. Furthermore, in synchronized HeLa cells, DNA synthesis was confirmed in the S phase. Moreover, increased expression of proliferating cell nuclear antigen (PCNA) was observed in Nm23-H1 siRNA treated HeLa cells after X-ray irradiation. In addition, Nm23-H1 was modified with SUMO-2 after X-ray irradiation. The present findings suggest that the reduction of Nm23-H1 is related to the decrease in sumoylation, which in turn, is involved in the induction of DNA synthesis via the regulation of PCNA expression after X-ray irradiation.

Proteomic analysis of anti-tumor effects by Rhizoma Paridis total saponin treatment in HepG2 cells

Rhizoma Paridis total saponin (RPTS) had been identified as the major components responsible for the anti-tumor effects of the herb Rhizoma Paridis, which had been used in China for centuries to treat many diseases including tumor. To elucidate the anti-tumor mechanism of RPTS, a proteomic analysis was carried out with RPTS treatment in HepG2 cells. More than 50 proteins showed a significant change between control (0.01% DMSO) and RPTS (IC(50) approximately 10microg/ml) treated cells after 48h. Twelve proteins had been identified by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) using peptide fingerprinting from 15 protein spots (density difference >2 fold between the control and RPTS-treated group). Among them, six proteins were down-regulated (dUTPase, hnRNP K, GMP synthase, etc.) and six proteins were up-regulated (DNase gamma, Nucleoside diphosphate kinase A, Centrin-2, etc.) by RPTS treatment in HepG2 cells as determined by spot volume (p<0.05). Most of the identified proteins were associated with tumor initiation, promotion, and progression. These findings might offer valuable insights into the mechanism of anti-tumor effect affected by RPTS treatment in HepG2 cells.