Increased extracellular matrix remodeling is associated with tumor progression in human hepatocellular carcinomas.

Matrix metalloproteinase-2 (MMP2) is a key enzyme in the process of extracellular matrix remodeling involved in tumor invasion and metastasis. The activation of MMP2 involves interplay with the membrane type-matrix metalloproteinase-1 (MT1-MMP) and the tissue inhibitor of metalloproteinase-2 (TIMP2). In vitro, activated hepatic stellate cells are a main source of MMP2 and collagen I induces MMP2 activation. The steady-state mRNA levels of MMP2, MT1-MMP, TIMP2, collagen I, collagen IV, and laminin gamma1 were compared with MMP2 activity in 55 hepatocellular carcinomas, 47 matching nontumor biopsies and 19 histologically normal livers. In hepatocellular carcinomas, increased collagen I mRNA levels were strongly associated with those of MMP2 (Spearman R =.74, P <.001), MT1-MMP (R =.65, P <.001) and TIMP2 (R = 0.61, P <.001). MMP2 activity was correlated with the mRNA expression of collagen I (R =.45 P <.01), collagen IV (R =.40, P <.01) and laminin gamma1 (R =.33, P <.05). Unlike collagen IV and laminin gamma1 mRNAs, MMP2, MT1-MMP, TIMP2, collagen I mRNA levels were increased in nonencapsulated compared with encapsulated tumors (P <.05). In addition, MMP2 activity was fourfold higher (P <.01) in tumors arising in cirrhotic livers than in those arising in noncirrhotic livers. Moreover, tumor recurrence was associated with 4.6- and 2.8-fold (P <.05) higher collagen I and MMP2 mRNA levels, respectively, in hepatocellular carcinomas arising in cirrhotic livers. Thus, a high extracellular matrix remodeling favors tumor progression in hepatocellular carcinomas.

Tumor progression is associated with a significant decrease in the expression of the endostatin precursor collagen XVIII in human hepatocellular carcinomas.

Endostatin inhibits angiogenesis and tumor growth in mice. The role of its endogenous precursor collagen XVIII in human cancer is unknown. In normal tissues, two variants of collagen XVIII, namely, the short and long forms regulate tissue specificity, the long form being almost exclusively expressed by hepatocytes in the liver. We analyzed RNA arrays from 57 hepatocellular carcinomas (HCCs) with common and variant-specific probes and investigated the relationships between collagen XVIII expression and angiogenesis by measuring the CD34-positive microvessel density. Low collagen XVIII expression by tumor hepatocytes was associated with large tumor size (r, -0.63; P < 0.001) and replacement of trabeculae with pseudoglandular-solid architecture (chi2, 28; P < 0.001), which indicate tumor progression. Tumors expressing the highest collagen XVIII levels were smaller and had lower microvessel density (P = 0.01) than those expressing moderate levels; and HCCs with the lowest collagen XVIII levels approached a plateau of microvessel density, which indicated that a decrease in collagen XVIII expression is associated with angiogenesis in primary liver cancer. HCCs recurring within 2 years of resection showed 2.2-fold lower collagen XVIII mRNA than nonrecurring ones (P = 0.02). The findings relied on the hepatocyte-specific long form. Thus, the endogenous expression of the endostatin precursor decreases along with tumor progression in HCCs.

Collagen XVIII is localized in sinusoids and basement membrane zones and expressed by hepatocytes and activated stellate cells in fibrotic human liver.

Type XVIII collagen is a recently discovered nonfibrillar collagen associated with basement membranes in mice and expressed at high levels in human liver. We studied the origin, distribution, and RNA levels of type XVIII collagen in normal and fibrotic human livers by in situ hybridization, immunohistochemistry, and Northern and dot blots and compared procollagen alpha1(XVIII) RNA levels with those of procollagen alpha1(IV) and laminin gamma1, the two major components of liver basement membranes. In normal liver, type XVIII collagen was heavily deposited in perisinusoidal spaces and basement membrane zones. The major source of type XVIII collagen was hepatocytes and, to a lesser extent, endothelial, biliary epithelial, and vascular smooth muscle cells and peripheral nerves. In cirrhosis, type XVIII collagen formed a thick deposit along capillarized sinusoids. Grain counts after in situ hybridization showed myofibroblasts to increase their expression 13-fold in active and twofold in quiescent fibrosis, whereas hepatocytes increased their expression only twofold in both active and quiescent fibrosis. Activated stellate cells in vitro expressed type XVIII collagen at high levels. These data indicate that type XVIII collagen is a component of the perisinusoidal space and is associated with basement membrane remodeling. Hepatocytes and activated stellate cells are important sources of type XVIII collagen in normal and fibrotic liver respectively, which suggests tissue-specific regulation of its expression.