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Parathyroid Hormone-like Peptide Shares Features with Members of the Early Response Gene Family: Rapid Induction by Serum, Growth Factors, and Cycloheximide¹

Departments of Clinical Biochemistry [E. T. A.], Medicine [D. J. D.], and Molecular and Medical Genetics [D. J. D.], and the Banting and Best Diabetes Centre [D. J. D.], University of Toronto, Toronto, Ontario, Canada

The parathyroid hormone-like peptide (PLP) gene is widely expressed in normal and neoplastic tissues. Previous studies have demonstrated that PLP gene expression is regulated by serum and cycloheximide, features common to the regulation of a number of different early response genes. We now report that PLP mRNA transcripts are induced within 5 min of exposure of rat keratinocytes to serum, return to control values at 20 min, and then increase and remain elevated for at least 4 h, following which they return to baseline levels. The PLP mRNA t was approximately 90 min in both serum-deprived and serum-stimulated cells. The serum induction was blocked by actinomycin D. Cycloheximide alone induced PLP gene expression; however, PLP mRNA transcripts were not superinduced in the presence of both serum and cycloheximide. Dexamethasone and 1,25-dihydroxyvitamin D₃ inhibited the basal levels of PLP mRNA transcripts but did not eliminate the serum induction of PLP gene expression. Epidermal growth factor or transforming growth factor-ß alone induced PLP mRNA transcripts, but no induction was observed following exposure of cells to epidermal growth factor and transforming growth factor-ß together. Treatment with 12-O-tetradecanoylphorbol-13-acetate for 90 min did not induce PLP mRNA transcripts, but 12-O-tetradecanoylphorbol-13-acetate blocked the rapid serum induction of PLP gene expression. These features of PLP gene expression suggest that PLP is a member of the growth factor-regulated early response gene family. The rapid serum stimulation of PLP gene expression raises the possibility that PLP may contribute in an autocrine fashion to the early cellular response to growth factor stimulation.

¹ E. T. A. is supported by a Natural Sciences and Engineering Research Council of Canada studentship, and D. J. D. is supported in part by a Career Scientist Award from the Ontario Ministry of Health. This work was supported by an operating grant from the National Cancer Institute of Canada.

² To whom requests for reprints should be addressed, at Toronto General Hospital, 200 Elizabeth Street CCRW 3-838, Toronto M5G 2C4, Ontario, Canada.

Received 11/19/91. Accepted 3/20/92.

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