Identification of NFIB as recurrent translocation partner gene of HMGIC in pleomorphic adenomas

Approximately 12% of all pleomorphic adenomas of the salivary glands are characterized by chromosome aberrations involving the chromosome segment 12q13-15. Several chromosomes have been found as translocation partners of chromosome 12, and some of these recurrently. Recently, the HMGIC gene was identified as the target gene affected by the 12q13-15 aberrations. Here, we report the identification and characterization of a new translocation partner gene of HMGIC in pleomorphic adenomas. 3'-RACE analysis of a primary adenoma with an apparently normal karyotype revealed an HMGIC fusion transcript containing ectopic sequences derived from the human NFIB gene, previously mapped to chromosome band 9p24.1. The HMGIC NFIB fusion transcript was also confirmed by RT-PCR. Since the chromosome segment 9p12-24 is repeatedly involved as translocation partner of chromosome 12q13-15 in pleomorphic adenomas, we tested whether NFIB might be a recurrent partner of HMGIC. RT-PCR analysis of a second adenoma with an ins(9;12)(p23;q12q15) as the sole anomaly, revealed that also in this tumor an HMGIC/NFIB hybrid transcript was present. The reciprocal NFIB/HMGIC fusion transcript, however, could not be detected in any of these tumors. Nucleotide sequence analysis of the fusion transcripts indicated that the genetic aberration in both tumors resulted in the replacement of a carboxy-terminal segment of HMGIC by the last five amino acids of NFIB. In conclusion, our results reveal the recurrent involvement of the NFIB gene as translocation partner gene of HMGIC in pleomorphic adenomas.