Parathyroid Hormone-related Protein Interacts with RNA

doi:10.1074/jbc.274.8.4832

Parathyroid Hormone-related Protein Interacts with RNA*

From the Departments of ^‡Medicine, ^‖Oncology, and ^**Microbiology and Immunology, McGill University, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montréal, Québec H3T 1E2, Canada

Abstract

Parathyroid hormone-related protein (PTHrP) is a secreted protein that acts as an autocrine and paracrine mediator of cell proliferation and differentiation. In addition to its biological activity that is mediated through signal transduction cascades, there is evidence for an intracellular role for PTHrP in cell cycle progression and apoptosis. These effects are mediated through a mid-region nuclear targeting sequence (NTS) that localizes PTHrP to the region of the nucleolus where ribonucleoprotein complexes form in vivo. In this work, we show that endogenous, transfected, andin vitro translated PTHrP proteins bind homopolymeric and total cellular RNAs at salt concentrations up to 1 m. A peptide representing the PTHrP NTS was effective in competing with the wild-type protein for RNA binding, whereas a similar peptide representing the nucleolin NTS was not. Site-directed mutagenesis revealed that the binding of PTHrP to RNA was direct and was dependent on preservation of a core GXKKXXK motif, embedded in the PTHrP NTS, which is shared with other RNA-binding proteins. The current observations are the first to document RNA binding by a secreted cellular protein and predict a role for PTHrP in regulating RNA metabolism that may be related to its localization in the nucleolus of cells in vivo.

Footnotes

↵* This work was supported in part by a grant from the Medical Research Council of Canada and by establishment funds from the Fonds de la Recherche en Santé du Québec (to J. E. H.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵§ Recipient of a studentship from the Medical Research Council of Canada.
↵¶ Supported by a challenge studentship from Manpower Canada.
↵‡ Medical Research Council of Canada Scholar supported by grants from the Medical Research Council of Canada and the Cancer Research Society of Canada.
↵§§ Chercheur Boursier of the Fonds de la Recherche en Santé du Québec. To whom correspondence should be addressed: Lady Davis Inst., Rm. 602, 3755 Côte Ste. Catherine Rd., Montréal, Québec H3T 1E2, Canada. Tel.: 514-340-8260/4986; Fax: 514-340-7573; E-mail: jhenders{at}ldi.jgh.mcgill.ca.
Abbreviations:

PTHrP

parathyroid hormone-related protein

PTH

parathyroid hormone

NTS

nuclear targeting sequence

RNP

ribonucleoprotein

hnRNP

heterogeneous nuclear ribonucleoprotein

KH

K homology

dsRNA

double-stranded RNA
- Received June 10, 1998.
- Revision received November 16, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.