Expression of Transcripts Encoding a Parathyroid Hormone-Related Peptide in Abnormal Human Parathyroid Tissues*

Abstract

A PTH-related peptide (PTHRP) has been identified and its cDNA cloned from human tumors associated with the syndrome of humoral hypercalcemia of malignancy. The human PTHRP gene has been recently isolated and found to be a complex transcriptional unit using multiple promoters and containing alternatively spliced 3' exons which result in three mRNA classes, each class encoding a PTHRP with a unique carboxy-terminus. The PTHRP gene appears to be expressed in a number of normal tissues, and PTHRP transcripts have been previously reported to be overexpressed in a small sample of human parathyroid adenomas. In the present study we surveyed RNA prepared from a total of 60 abnormal human parathyroid glands for PTHRP gene expression using a combination of Northern blotting and RNase protection techniques. Apparent overexpression of PTHRP mRNA was observed in two thirds of parathyroid adenomas, whereas no overexpression was found in 7 examples of sporadic primary hyperplasia, 5 examples of secondary hyperplasia, and 3 examples of parathyroid carcinoma. Apparent overexpression was also observed in 1 of 4 cases of multiple endocrine neoplasia type 1, 1 of 2 examples of multiple endocrine neoplasia type 2, and 1 gland considered to represent tertiary hyperparathyroidism. Northern analysis of poly(A)+ RNA prepared from three representative adenomas using region-specific probes indicated that two putative promoters are used and revealed a pattern of preferential splicing of transcripts to include the most distal 3' exon. These findings suggest that the PTHRP gene is commonly overexpressed in adenomatous parathyroid glands, but not in sporadic primary hyperplasia, that this overexpression does not seem to be dependent on the use of a single specific promoter, and that adenomatous parathyroid cells appear to preferentially use one of several alternative splicing pathways. It is presently not known whether PTHRP is secreted by abnormal parathyroid tissues and, if so, in what form.