Preferential Loss of the Nonimprinted Allele for the ZAC1 Tumor Suppressor Gene in Human Capillary Hemangioblastoma

Capillary hemangioblastomas (CHBs) are vascular, usually benign, tumors of the CNS, occurring either as a component of familial von Hippel-Lindau (VHL) disease or as a sporadic entity. Both familial and sporadic forms of VHL-associated tumors involve inactivation of the VHL gene; for CHB, 20% to 50% of sporadic cases are affected. However, other molecular alterations involved in the pathogenesis of sporadic CHBs, which represent up to 70% of CHBs, remain largely unknown. We previously identified a minimal deleted area at 6q23-24 in CHB, and the present study focused on the ZAC1 gene (6q24-25). ZAC1 is a maternally imprinted tumor suppressor gene with antiproliferative properties. We investigated loss of heterozygosity (LOH), promoter methylation, and expression status of ZAC1 in mainly sporadic cases of CHB. Our LOH analysis with 6 microsatellite markers spanning the ZAC1 gene region revealed a high frequency (6 of 10, 60%) of LOH. The promoter methylation analysis detected predominance of the methylated ZAC1 sequence in the majority (9 of 10, 90%) of the tumors. Immunohistochemistry exhibited a strongly reduced expression of ZAC1 in stromal cells of all CHBs studied. Collectively, our current results indicate that the absence of the unmethylated ZAC1 sequence was highly concurrent with ZAC1 region LOH or 6q loss and with lack of ZAC1 expression, suggesting preferential loss of the nonimprinted, expressed ZAC1 allele in CHB. This novel finding highlights the importance of ZAC1 in development of CHB, particularly in non-VHL-associated cases.