Enhancement of chemical hepatocarcinogenesis by the HIV-1 tat gene

Abstract

The human immunodeficiency virus-1 Tat protein is suspected to be involved in the neoplastic pathology arising in AIDS patients. tat-transgenic (TT) mice, which constitutively express Tat in the liver, develop liver cell dysplasia (LCD) that may represent a preneoplastic lesion. To test if TT mice are predisposed to liver carcinogenesis, we treated them with diethylnitrosamine, a hepatotropic carcinogen. Diethylnitrosamine-treated TT mice developed both preneoplastic and neoplastic lesions in the liver. They showed an enhancement of LCD and developed basophilic liver cell nodules (BLCN), hepatocellular adenomas (HA), and hepatocellular carcinomas (HC). Both preneoplastic (LCD and BLCN) and neoplastic (HA and HC) lesions were significantly more frequent in TT than in control mice: 29.7% versus 12.7% for LCD, 57.9% versus 23.3% for BLCN, 40.6% versus 10.0% for HA, and 50.0% versus 12.7% for HC. These results indicate that Tat expression in the liver predisposes to both initiation of hepatocarcinogenesis and to malignant progression of liver tumors. This study supports a role for Tat in enhancing the effect of endogenous and exogenous carcinogens in human immunodeficiency virus-1-infected patients, thereby contributing to tumorigenesis in the course of AIDS.

Figure 1.

Analysis of tat DNA (A) and RNA (B) by PCR and RT-PCR. After DNA amplification, the samples were run in agarose gel electrophoresis and stained by ethidium bromide. A: Lane 1, negative control; lanes 2 and 3, LCD; lane 4, BLCN; lane 5, HA; lane 6, HC; lane 7, T53 cell line constitutively expressing tat; lane 8, molecular weight markers XIV (Boehringer). B: Lane 1, negative control, lanes 2 and 3, LCD; lane 4, BLCN; lane 5, HA; lanes 6 and 7, HC treated and untreated with reverse transcriptase, respectively; lane 8, T53 cell line constitutively expressing tat; lane 9, molecular weight markers XIV (Boehringer). The band of 239 bp (arrow) is the tat amplification product. The lower band represents the primers which migrated at the bottom of the gel.

Figure 2.

Figure 2 ▶ . Liver cell proliferative lesions. A and B: LCD. Lobular architecture is retained with the portal tract and central vein normally located. Dysplastic hepatocytes show nuclear pleomorphism and are often binucleated. H&E; original magnifications, ×63 (A), ×400 (B). C and D: BLCN. Foci of dysplastic hepatocytes with basophilic cytoplasm surround frequently the central vein; no sharp outline separates the abnormal foci from adjacent normal hepatocytes. H&E; original magnifications, ×25 (C), ×160 (D). E and F: HA. The adenoma compresses surrounding normal liver cells; plates of neoplastic hepatocytes form trabeculae separated by sinusoid-like vessels. Nuclear atypia and mitoses are evident. H&E; original magnifications, ×160 (E), ×400 (F). G: HA. Electron micrograph illustrating the fine structure of adenoma cells. S, sinusoidal surface; arrowhead, bile canaliculus. The Disse space is reduced and adenoma cells lack microvilli. Bile canaliculus is irregularly dilated with few and thick microvilli. Original magnification, ×3000.

Figure 3.

HC. A: Trabecular pattern with cords of neoplastic cells showing acinar or pseudoglandular structures. B: Neoplastic hepatocytes contain hyaline inclusions in the cytoplasm. C: Solid poorly differentiated carcinoma with great variability of nuclei showing giant polynucleated cells and necrosis. D: Electron micrograph showing the fine structure of a differentiated hepatocarcinoma: neoplastic cells are not polarized; no bile canaliculus is evident. E: Nodular metastases (N) of HC in lung tissue. H&E; original magnifications: ×160 (A), ×250 (B), ×400 (C), ×25 (E), and ×2500 (D).

Figure 4.

Incidence of proliferative liver lesions in mice treated with two DENA inoculations, related to the time of examination.