Role of L2DTL, cell cycle-regulated nuclear and centrosome protein, in aggressive hepatocellular carcinoma

L2DTL is a human ortholog of Drosophila lethal (2) denticleless, l(2)dtl. This study is to elucidate its function and clinicopathological significance in hepatocelllular carcinoma (HCC) progression. We used RT-PCR, immunostaining, Western blotting, and centrosome isolation to determine the L2DTL expression and protein localization, and RNAi to analyze its role in tumor cell growth. L2DTL protein located to the nucleus in interphase and centered to centrosomes, with colocalization of γ-tubulin and Aurora-A, throughout the cell cycle, and cofractionated with γ-tubulin. L2DTL gene expression increased during G₁/S phase, and the DNA sysnthesis in liver regeneration. L2DTL protein decreased in mitosis via degradation by the APC/C-Cdh1 complex. L2DTL was downregulated in the induced differentiation of HepG2 and NT2 cells. L2DTL downregulation by RNAi oligos led to reduced cancer cell growth and invasion capability in vitro, in which microarray analysis disclosed dysregulation of genes involved in cell cycle regulation, chromosome segregation, and cell division. L2DTL overexpressed in 59% of 270 resected, unifocal, primary HCCs. L2DTL overexpression correlated with bigger tumor (p=0.000003), high-grade (p=0.00003), and high-stage tumors with portal vein invasion (p=1×10 ^-8). L2DTL overexpression was associated with a lower 10-year survival, particularly in the p53-mutated HCCs (p=0.00006). In conclusion, L2DTL encodes a nuclear protein with centrosome targeting in mitosis, and plays important roles in DNA synthesis, cell cycle progression, cytokinesis, proliferation, and differentiation. L2DTL overexpression is associated with enhanced metastatic potential of HCC, and contributes synergistically with p53 mutation, which leads to the loss of p53-governed checkpoints, toward advanced HCC with poor prognosis.