Insertional Activation of GLI2 in Adult T-Cell Leukemia/Lymphoma.

Retroviruses induce cancer by integrating into the cellular genome and activating oncogenes or inactivating tumor suppressor genes. Human T-cell Leukemia Virus type 1 (HTLV-1), a complex retrovirus, induces Adult T-cell Leukemia/Lymphoma (ATLL) after a latency of over 30 years and in only 5% of carriers. The long latency and incomplete penetrance is similar to how slow transforming retroviruses induce cancer in mice and imply multiple oncogenic “hits” need to accumulate for clinically apparent disease. Insertional mutagenesis may be one mechanism by which ATLL develops. We used splinkerette-PCR to clone and map insertion sites from an HTLV-1 infected T-cell line, Hut-102. We identified an HTLV-1 insertion 5′ of the GLI2 gene, formerly known as Tax-Helper-Protein-1. We found GLI2 was up-regulated by promoter insertion. Interestingly, we found GLI2 protein occupied the HTLV-1 Long Terminal Repeat. The effect of GLI2 expression on viral expression was investigated by knockdown of GLI2 in Hut-102 cells. Our results show that retroviral insertional mutagenesis can be an important mechanism in HTLV-1-induced leukemias and lymphomas.