Abstract
Parathyroid hormone-related protein (PTHrP) is a normal secretory product of a variety of squamous epithelia, including epidermal keratinocytes. Only a subset of squamous carcinomas, however, express the gene at levels sufficient to cause humoral hypercalcemia. In the present study, comparison of PTHrP expression levels with p53 functional status in a series of squamous carcinoma lines has revealed an association between expression of specific mutant isoforms of p53 and very low levels of PTHrP mRNA. Evaluation of p53 isoforms with mutations in codons 248 and 273 showed them to be capable of repressing PTHrP gene expression in a high-expressing, p53-negative squamous line by approximately 50%. Conversely, inactivation of an endogenous mutant p53 with E1B proteins resulted in an increase in PTHrP expression in a low-expressing cell line. Subsequent analysis of promoter-specific PTHrP transcripts in a p53-negative squamous line transfected with mutant p53 isoforms suggested that down-regulation occurred primarily at the two TATA-based promoters. Direct testing of a murine PTHrP reporter construct in transient transfection assays confirmed the capacity of the 248 and 273 mutants to repress this TATA-based promoter, although only about half as effectively as wild-type p53.
Footnotes
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↵1 This work was supported by American Cancer Society Grant BE-152D (W. M. P.), The Ruth Estrin Goldberg Memorial for Cancer Research (W. M. P.), and NIH National Research Service Award CA63765 (J. F.) and CIA Grant CA60498 (J. J. W.).
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↵2 To whom requests for reprints should be addressed, at Section of Endocrinology and Metabolism, Department of Internal Medicine, Yale University School of Medicine, P. O. Box 3333, New Haven, CT 06520-8020. Phone: (203) 785-6425, (203) 785-5488; Fax: (203) 785-6015.
- Received March 28, 1996.
- Accepted July 2, 1996.
- ©1996 American Association for Cancer Research.
Volume 56, Issue 17
