Introduction: Chronic active Hepatitis C (Hep C) is the most potent correlate to the development of hepatocellular carcinoma (HCC). Unfortunately, the mechanism behind hepatitis-associated cancer remains elusive. Early detection is imperative and in select patients the cancer is curable. Oxidative stress and DNA damage are known to occur in hepatitis and in this regard the liver plays a central role in nucleic acid metabolism. Autotaxin, important in ATP and purinergenic pathways, has been linked to tumor invasion and metastasis in several human cancers. The objective of this study was to evaluate key elements in nucleic acid metabolism that might account for the biologic behavior of hepatitis associated cancer.
Methods: Liver tissue was collected prospectively from three patient subtypes: 1) Patients undergoing liver resection for non-hepatitis related disease 2) Hep C patients transplanted without cancer and 3) Hepatitis C patients with biopsy-proven HCC. Total RNA was isolated and tested for integrity using the Agilent system. Affymetrix human gene chip, HG-U133 microarray analysis was carried out on 18 samples using 20 ug of total RNA and focusing on purine metabolic pathways that might differentiate the three clinical groups. Samples were run in triplicate to assure accuracy. Only probe sets called “present” by MAS5 in at least half of the arrays were analyzed. Differences between groups were tested by ANOVA. A p-value of <0.05 was used to determine significance.
Results: Within purine metabolism, several genes were differentially expressed between normal liver and both Hep C groups. Of these, Autotaxin was significantly elevated in patients with cancer vs. Hep C patients without cancer or normal liver (p= 0.01). In addition, CDC42EP3, CDC42EP5, and CDC42SE1, Rho GTPase binding proteins associated with lypophosphatidic acid receptor (LPA) signaling, were also differentially over-expressed in hepatitis C patients (p = 0.0009, p=0.001, p=0.009, respectively). LPA, a target of ENPP2, is known to stimulate cancer cell motility and invasion by signaling pathways that activate RHO GTPases.
Conclusions: Autotaxin is differentially expressed in patients with hepatocellular cancer compared to Hep C patients without cancer or normal liver. Autotaxin is a tumor cell motility-stimulating factor and one of very few genes within the purine metabolic pathway that is up-regulated in hepatitic patients with cancer vs. their non-tumor bearing counterparts. Receptor signaling pathways linked to ENPP2 are also differentially over-expressed. ENPP2 may be a novel marker for early stage HCC in Hep C-infected liver.