Identification Of Lipocalin 2 In Human Hepatoblastoma

Cancer is the leading cause of medical death in children. Hepatoblastoma is the most common type of pediatric liver malignancy. Although it is a rare tumor, it often presents in advanced stage and is associated with a poor prognosis. It is well known that signaling abnormalities in the beta catenin pathway are associated with 90% of these tumors. We have recently shown activation of Yes associated protein (Yap) in this tumor type. In fact b‐catenin‐Yap co‐activation was observed in 80% of hepatoblastoma patients. Co‐expression of Yap and b‐catenin also led to hepatoblastoma in mice. To elucidate downstream targets of Yap and b‐catenin that may contribute to tumorigenesis, we performed gene array analysis using mRNA isolated from mice tumors. The most upregulated genes were assessed for presence of classical transcription factors that bind b‐catenin (TCF4) and Yap (TEAD). This analysis revealed lipocalin 2 among the top 5 candidates. Lipocalin 2, or NGAL (neutrophil gelatinous associated lipocalin) is a small molecule protein with known antibacterial properties, and is also used as a biomarker in kidney injury. Recently, it has been found to be expressed in a variety of adult cancers including breast, colon, pancreatic, and hepatocellular carcinoma. We used a tissue microarray of 74 patient hepatoblastoma samples from a tertiary care Pediatric Hospital to evaluate the presence of lipocalin 2 by immunohistochemistry. The tumors were classified by histology type and the degree of lipocalin staining was graded on a 0–3 scale. Lipocalin 2, which is normally not expressed in human liver (except for Kupffer cells), was found to be present in the nucleus or cytoplasm of 70 (95%) of the pediatric hepatoblastoma samples. Most hepatoblastoma samples (69%) showed greater than 1 histological component within the tumor tissue. The degree of staining for lipocalin 2 varied within each sample based on tumor histology. All embryonal components were strongly positive for lipocalin 2 with staining scores of 2–3. Ninety‐Six percent of crowded fetal histology components had positive staining, although the staining ranged from 1–2 in intensity. All components of blastema histology were negative and small cell undifferentiated components had only 18% positive lipocalin 2 expression. Next, cell lysates from a human hepatoblastoma cell line (HepG2) were examined for lipocalin 2 and showed notable expression as well. Thus, we have identified increased expression of lipocalin 2 downstream of b‐catenin and Yap activation in hepatoblastoma cells and in patient tissues. Lipocalin 2 may be playing an important role in b‐catenin‐Yap driven hepatoblastoma development.