Expression of L-type amino acid transporter I (LAT1) and 4F2 heavy chain (4F2hc) in liver tumor lesions of rat models

Background and Objectives: It has been said that amino acid transporters play an important role in supplying nutrition to cells and for cell proliferation. In this study, we examined whether LAT1 and 4F2hc are closely related to tumor growth. Methods: Rat colon cancer cells (RCN-9) were injected into the spleen of 12 male rats (inbred F344/DuCrj). In each rat, liver samples including tumor lesions were immunostained with anti-LAT1 and anti-4F2hc antibodies. The staining area of LAT1 and 4F2hc tumor lesions was calculated by computer analysis. Results: Sixty-eight tumor nodules were observed in 12 livers. Out of the 68 tumor nodules, 36 nodules (52.9%) indicated a positive staining of LAT1 and 32 (47.1%) had a negative staining of LAT1. However, the LAT1 expression was scarcely detected in non-tumor areas. In terms of the 4F2hc expression, there were 56 nodules (82.4%) with 4F2hc positive and 12 (17.6) with 4F2hc negative. In addition, the expression of 4F2hc in nontumor areas was almost the same as the expression of 4F2hc in tumor lesions. The average tumor size of the group with LAT1 positive and 4F2hc positive (n = 31) was 0.845 ± 0.232 mm², which was significantly larger than that of the group with LAT1 negative and 4F2hc negative group (n = 7) (0.090 ± 0.028 mm²) or the group with LAT1 positive and 4F2hc negative (n = 5) (0.097 ± 0.025 mm²), respectively (P = 0.0017, P = 0.007). Conclusion: LAT1 was related to tumor growth. We think that LAT1 can possibly enhance its ability to promote tumor growth in cooperation with 4F2hc.