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Nm23 and tumour metastasis: basic and translational advances
J M Freije1, N J MacDonald, P S Steeg
1Women's Cancers Section, National Cancer Institute, Bethesda, MD 20892, USA.
Abstract:
The nm23 genes were discovered on the basis of their reduced expression by highly metastatic cell lines. This trend was confirmed in cohorts of several types of human carcinomas and melanomas. Several transfection studies have demonstrated the suppressive effect of nm23 overexpression on the metastatic aggressiveness of melanoma and breast carcinoma cells in vivo. These transfection experiments have also demonstrated an effect of nm23 overexpression on cellular functions involved in the metastatic phenotype, such as cell motility, and point to a regulatory role for Nm23 proteins in cellular signalling pathways. Nm23 homologues from various species are also involved in normal tissue development and differentiation. Transfection of nm23-H1 into breast cancer cells provided a functional demonstration of the involvement of this gene in the differentiation of mammary epithelial cells. However, the molecular mechanism of these biological effects remains unknown. Several biochemical activities have been reported for Nm23, including NDP kinase activity, serine autophosphorylation and protein-histidine kinase activity. To define the possible significance of these biochemical activities, we carried out site-directed mutagenesis of the relevant codons of nm23-H1 cDNA and studied the effects upon transfection into MDA-MB-435 human breast carcinoma cells. We have also used Nm23 expression as a molecular marker to identify novel compounds that are active against the most aggressive tumour cells. This approach revealed that none of the standard agents currently in clinical use is preferentially active against the most aggressive tumour cells, and allowed us to identify new compounds that are preferentially inhibitory towards low-Nm23-expressing breast carcinoma and melanoma cell lines. This analysis also revealed a significant correlation between Nm23 levels and sensitivity of the tumour cells to alkylating agents. A functional implication of Nm23 proteins in this phenomenon was demonstrated after transfection of nm23 cDNAs into melanoma and breast and ovarian carcinoma cells.
Insights
The nm23 gene, linked to reduced metastasis in cancers like melanoma and breast carcinoma, plays a role in cell differentiation and signaling. Its expression levels correlate with tumor cell sensitivity to certain chemotherapy agents.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Metastasis Research
Background:
- The nm23 gene family was identified due to its decreased expression in highly metastatic cancer cell lines.
- Reduced nm23 expression is observed across various human carcinomas and melanomas, correlating with metastatic potential.
- nm23 gene products are implicated in normal tissue development and cellular differentiation processes.
Purpose of the Study:
- To investigate the functional significance of nm23 gene products in cancer metastasis and cellular functions.
- To explore the biochemical activities of nm23 proteins, such as NDP kinase and kinase activities, and their role in biological effects.
- To identify novel therapeutic compounds targeting aggressive tumor cells by utilizing nm23 expression as a molecular marker.
Main Methods:
- Site-directed mutagenesis of nm23-H1 cDNA was performed to study the effects of specific biochemical activities.
- Transfection studies using nm23-H1 and nm23 cDNAs were conducted in various cancer cell lines (breast carcinoma, melanoma, ovarian carcinoma).
- Nm23 expression levels were used as a marker to screen for compounds selectively active against aggressive tumor cells.
Main Results:
- Overexpression of nm23 suppressed metastatic aggressiveness and affected cell motility in melanoma and breast carcinoma cells.
- nm23-H1 transfection demonstrated its involvement in the differentiation of mammary epithelial cells.
- The study identified novel compounds preferentially inhibiting low-nm23-expressing tumor cells and revealed a correlation between nm23 levels and sensitivity to alkylating agents.
Conclusions:
- Nm23 proteins play a crucial role in regulating cancer cell metastasis, differentiation, and signaling pathways.
- Understanding the biochemical activities of nm23 is essential for elucidating its molecular mechanisms in cancer.
- Nm23 expression serves as a valuable biomarker for identifying potential therapeutic targets and predicting sensitivity to specific chemotherapeutic agents, particularly alkylating agents.