Neutrophil gelatinase-associated lipocalin (NGAL), also known as lipocalin 2, is a 25-kDa lipocalin initially purified from neutrophil granules. It is thought to play a role in regulating cellular growth since its expression is highly upregulated in a variety of proliferative cells such as cancer cells. However, experimental evidence showing a clear causal relationship between NGAL expression and the proliferation of tumor cells is lacking. Here, we found NGAL expression in highly and poorly metastatic colon cancer cell lines of the same genetic origin correlated inversely with the metastatic potential of these cells, which suggests NGAL participates in the metastatic process. To explore the role NGAL plays in tumor growth and metastasis, the KM12SM human colon cancer cell line, which is highly metastatic while showing decreased NGAL expression, was genetically manipulated to overexpress NGAL. The effects of this on tumor growth and liver metastasis were then analyzed using experimental animal models established by injecting BALB/c nude mice with tumor cells subcutaneously or intrasplenically. Ectopic expression of NGAL in the colon cancer cells had little effect on the growth and viability of the tumor cells both in vitro and in vivo. However, NGAL expression not only suppressed the ability of the colon carcinoma cells to invade Matrigel in vitro, it also substantially inhibited liver metastasis in an experimental animal model. Collectively, these results indicate that NGAL may be a candidate metastasis suppressor in colon cancer cells. ' 2005 Wiley-Liss, Inc.

Abstract. Lipocalin 2 (Lcn2) has been reported to induce cellular proliferation based on its expression in a variety of proliferative cells. Consistent with these findings, the present study demonstrates a significant increase in Lcn2 levels in human hepatocellular carcinoma (HCC) tissues compared with non-tumor liver tissues. However, the role of Lcn2 in hepatocarcinogenesis is far from clear. To investigate the effects of Lcn2 expression on hepatocarcinogenesis, Chang liver and SK-Hep1 HCC cell lines were genetically manipulated to express Lcn2, and the effects on the proliferation and invasion of HCC cells were analyzed. Ectopic expression of Lcn2 in HCC cells significantly inhibited the growth of HCC cells in vitro and in vivo, reduced the invasive potential of cells, and inhibited the expression of matrix metalloproteinase 2 (MMP-2). Lcn2 may exert its function partly through the inhibition of the c-Jun N-terminal kinase (JNK) and phosphatidyl inositol 3'-kinase (PI3K)/Akt signaling pathways in HCC cells. The selective inhibition of these pathways using pharmacological inhibitors significantly inhibited proliferation, invasion and MMP-2 expression, whereas Lcn2 expression suppressed the JNK and PI3K/Akt pathways. Collectively, these results clearly indicate that Lcn2 may play a protective role against the progression of HCCs by suppressing cell proliferation and invasion. The clinical significance of the present findings should be evaluated further.