Significance of downregulation of liver fatty acid-binding protein in hepatocellular carcinoma.

AIM: To investigate the significance of downregulation of liver fatty acid-binding protein (L-FABP) expression in hepatocellular carcinoma (HCC).
METHODS: Tissue microarrays of 146 cases of HCC were used to perform immunohistochemical staining for L-FABP. For each L-FABP-negative HCC, further immunohistochemical staining was performed using a representative whole-tissue section to confirm the downregulation of L-FABP expression and to assess the intratumoral heterogeneity of the staining pattern. Clinical data were retrieved from the clinical files, and histological slides were reviewed. Immunohistochemical staining for cytokeratin (CK) 7, CK 19, β-catenin, glutamine synthetase (GS), and serum amyloid A were also performed on the tissue microarrays. Clinicopathological features of the L-FABP-negative and L-FABP-positive HCC cases were compared. Furthermore, L-FABP and GS gene expression in HCC and cholangiocarcinoma cell lines were analyzed using real-time reverse transcription polymerase chain reaction. Mutation analysis of HNF1A [encoding hepatocyte nuclear factor 1 (HNF1)α] was performed for L-FABP-negative HCC cases.
RESULTS: Sixteen (10.9%) of the 146 cases of HCC stained negative for L-FABP. When we examined the correlation between the downregulation pattern of L-FABP and tumor size, most cases of smaller HCC (≤ 2 cm in diameter) exhibited focal downregulation, while most cases of larger HCC (> 2 cm in diameter) exhibited diffuse downregulation. The correlation was statistically significant (P = 0.036). When the HCC was smaller, the L-FABP-negative area often corresponded to a "nodule-in-nodule" appearance. Among the small HCC cases, tumor differentiation was significantly lower, and the frequency of intratumoral inflammation was significantly lower in L-FABP-negative cases than in L-FABP-positive cases (P = 0.032 and P = 0.009, respectively). The frequency of positivity for β-catenin and GS staining was significantly higher in L-FABP-negative cases of small HCC than in L-FABP-positive cases of small HCC (P = 0.009 and P = 0.000, respectively). Among six HCC cell lines examined, four showed higher expression of L-FABP, and the remaining two cell lines showed lower or no expression of L-FABP. Two of the 16 L-FABP-negative HCC cases possessed a mutation in exon 4 of HNF1A.
CONCLUSION: In smaller HCC, L-FABP downregulation probably occurs because of phenotypic changes during tumor progression. Moreover, this downregulation correlated with tumor differentiation and intratumoral inflammation.