Loss of heterozygosity at the mannose 6-phosphate/insulin-like growth factor 2 receptor locus: a frequent but late event in adrenocortical tumorigenesis.

Abstract

Recent studies have pointed to the role of the IGF system in adrenocortical tumorigenesis. The IGF-II gene is overexpressed in malignant adrenocortical tumors and its proliferative effects are mediated by the type-1 IGF receptor (IGF1R). The mannose 6-phosphate/IGF2 receptor (M6P/IGF2R) plays a key role in regulating cell growth, by ensuring the clearance and inactivation of IGF-II and facilitating activation of the growth inhibitor, transforming growth factor beta (TGFbeta1). The M6P/IGF2R has been implicated as a tumor suppressor gene in various human tumors. The purpose of this study was to determine if the M6P/IGF2R is involved in adrenal tumorigenesis. Two polymorphisms in the 3' untranslated region of M6P/IGF2R were used to screen a large series of 76 sporadic adrenocortical tumors for loss of heterozygosity (LOH) by PCR amplification of DNA. Tumors were classified into three groups based on pathological features: benign tumors (n=25), suspect tumors (n=22) and malignant tumors (n=29). LOH at the M6P/IGF2R locus was detected in 15 of 57 (26%) informative tumors and was more frequent in malignant tumors (58%) than in benign and suspect tumors (9 and 13% respectively). These findings provide evidence that LOH at the M6P/IGF2R locus is a frequent event in adrenocortical tumors and support the hypothesis that it may function as a tumor suppressor gene in adrenocortical tumorigenesis.