1795

Previously, we demonstrated that the transcription factor LOT1, also known as PLAGL1/ZAC1, has growth suppressive effects in carcinoma cell lines. Here, we provide additional evidence to support the gene’s potential role in cancer. We evaluated LOT1 gene expression in malignant ovarian epithelium obtained from frozen human ovarian tumor tissues using laser capture microdissection (LCM) and real-time PCR techniques. Our analysis revealed that LOT1 mRNA expression was not detectable in 12 of 31 (39%) cases of ovarian cancer and was variable between the remaining 19 tumor specimens. These findings are consistent with previous data that showed altered expression of the LOT1 gene in different human carcinoma cell lines. In addition, based on the information that the gene is localized on chromosome 6q24-25 which is a common site for LOH in many solid tumors, we examined whether LOT1 is indeed a candidate gene in this region deleted in cancer. We used highly frequent single nucleotide polymorphic sites within the LOT1 gene for PCR, followed by direct sequencing, to determine the occurrence of allelic imbalance in a series of surgically resected carcinomas. The informative samples showed allelic deletion of this gene in ovarian and breast tumors with a frequency of 36.5% and 40%, respectively. Analysis of the CpG dinucleotides in the LOT1 genome, however, showed 100% methylation of this gene in only about 12.5% of the tumor samples with LOH at the gene locus. These observations, together with the expression data suggest that, although many tumors show loss of one LOT1 allele, in some cases the gene must have been silenced by certain mechanism(s) other than retention of the methylated allele.

[Proc Amer Assoc Cancer Res, Volume 45, 2004]