Brain-type and liver-type fatty acid-binding proteins: new tumor markers for renal cancer?

Abstract

Background: Renal cell carcinoma (RCC) is the most common renal neoplasm. Cancer tissue is often characterized by altered energy regulation. Fatty acid-binding proteins (FABP) are involved in the intracellular transport of fatty acids (FA). We examined the level of brain-type (B) and liver-type (L) FABP mRNA and the protein expression profiles of both FABPs in renal cell carcinoma.

Methods: Paired tissue samples of cancerous and noncancerous kidney parts were investigated. Quantitative RT-PCR, immunohistochemistry and western blotting were used to determine B- and L-FABP in tumor and normal tissues. The tissue microarray (TMA) contained 272 clinico-pathologically characterized renal cell carcinomas of the clear cell, papillary and chromophobe subtype. SPSS 17.0 was used to apply crosstables (chi2-test), correlations and survival analyses.

Results: B-FABP mRNA was significantly up-regulated in renal cell carcinoma. In normal tissue B-FABP mRNA was very low or often not detectable. RCC with a high tumor grading (G3 + G4) showed significantly lower B-FABP mRNA compared with those with a low grading (G1 + G2). Western blotting analysis detected B-FABP in 78% of the cases with a very strong band but in the corresponding normal tissue it was weak or not detectable. L-FABP showed an inverse relationship for mRNA quantification and western blotting. A strong B-FABP staining was present in 52% of the tumor tissues contained in the TMA. In normal renal tissue, L-FABP showed a moderate to strong immunoreactivity in proximal tubuli. L-FABP was expressed at lower rates compared with the normal tissues in 30.5% of all tumors. There was no correlation between patient survival times and the staining intensity of both FABPs.

Conclusion: While B-FABP is over expressed in renal cell carcinoma in comparison to normal renal tissues L-FABP appears to be reduced in tumor tissue. Although the expression behavior was not related to the survival outcome of the RCC patients, it can be assumed that these changes indicate fundamental alterations in the fatty metabolism in the RCC carcinogenesis. Further studies should identify the role of both FABPs in carcinogenesis, progression and with regard to a potential target in RCC.

Figure 1

B-FABP immunohistochemistry. (A) In normal tissue B-FABP is preferentially expressed in proximal tubuli. B-D Clear cell carcinomas without (B), weak to moderate immunoreactivity (C) and strong expression of B-FABP (D).

Figure 2

L-FABP immunohistochemistry. (A) In normal tissue L-FABP is preferentially expressed in proximal tubuli. B-D Clear cell carcinomas without (B), weak to moderate immunoreactivity (C) and strong expression of L-FABP (D).

Figure 3

FABP mRNA expression. FABP mRNA expression in matched normal (NN) and malignant (NC) RCC tissue samples. Expression data were normalized against the geometric means of the two reference genes PPIA and TBP. Statistical differences were calculated by the Wilcoxon test. (A) B-FABP, (B) L-FABP mRNA expression.

Figure 4

Western blot detection of FABP. FABP and β-Actin in matched normal (NN) and malignant (NC) RCC tissue samples. (A) B-FABP, (B) L-FABP.

Figure 5

Kaplan-Meier survival curves for B- and L-FABP mRNA expression. The mRNA over-expression above and below the median was compared for all cases. (A) for B-FABP and (B) for L-FABP.

Figure 6

Kaplan-Meier survival curves for tumor stage and Fuhrman grades in the TMA cohort. (A) Survival curves for tumor stage. Tumors with stage 1 and 2 (blue line) revealed significantly longer survival times if compared to those with high stage 3 and 4 (green line). (B) Survival curves for Fuhrman grades. Tumors with grade 1 and 2 (blue line) revealed significantly longer survival times if compared to those with high grade 3 and 4 (green line).

Figure 7

Kaplan-Meier survival curves for B- and L-FABP expression in the TMA cohort. Positive and negative FABP expression was compared for all cases. (A) B-FABP expression and (B) L-FABP expression.