Structural and Physiologic Characterization of the Mid-region Secretory Species of Parathyroid Hormone-related Protein

Abstract

Parathyroid hormone-related protein (PTHrP) is initially translated as a preprohormone which is posttranslationally processed to yield a family of mature secretory forms. Most attention has focused on the aminoterminal portion of the molecule which is homologous to parathyroid hormone. It is clear, however, that a midregion species of PTHrP is posttranslationally cleaved from the highly conserved mid-region of PTHrP, and that the amino terminus of this peptide is Ala 38 . The purposes of the current study were three: 1) to confirm that Arg 37 immediately preceding Ala 38 serves as a posttranslational processing site in the PTHrP precursor, 2) to determine the carboxyl terminus of the mid-region secretory species of PTHrP, and 3) to synthesize this authentic mid-region secretory form of PTHrP and determine whether it is biologically active. The results indicate that: 1) Arg 37 is indeed a processing site in the PTHrP precursor; 2) three distinct mid-region PTHrP species are generated by posttranslational processing, PTHrP(38 -94)amide, PTHrP(38 -95), and most likely, PTHrP(38 -101); and 3) synthetic mid-region PTHrP(38 -94)amide is active in four different biological systems. These studies confirm the finding that PTHrP is a prohormone. More importantly, they define a novel, biologically active highly conserved mid-region secretory form of PTHrP.Parathyroid hormone-related protein (PTHrP) 1 was initially discovered through its structural and functional homology with parathyroid hormone (for a review, see Refs.

Nuclear targeting of a midregion PTHrP fragment is necessary for stimulating growth in breast cancer cells

“…24,31 The midregion peptides were tested on MCF-7 and MDA-MB231 cells to confirm calcium signalling induction. Scrambled(1NLS) was used as a negative control.…”

“…24,31 Despite the evidence for biological activity and second messenger signalling, the extracellular receptor for this peptide has not been identified to date.…”

“…Studies focusing on midregion PTHrP identified it to be a secretory peptide, [20][21][22][23] with amino acids sequences of 38-94, 38-95 or 38-101. 24 PTHrP has also been associated with an intracrine role that is dependent on the bipartite nuclear localisation sequence (NLS) located in amino acids 88-106, 25,26 which following post-translation processing of PTHrP results in the NLS-(88-101) remaining within midregion PTHrP-(38-101) peptide. Nucleus/nucleolus targeting of PTHrP has been shown in a wide variety of cells.…”

PTHrP Produced by Myeloma Plasma Cells Regulates Their Survival and Pro-Osteoclast Activity For Bone Disease Progression

“…Furthermore, by using rabbit anti-mid-region PTHrP, we specifically revealed a single band of approximately 7 kDa related to the mid-region, as described for other tumors. (9)(10)(11)(23)(24)(25) We also measured RNA levels of both PTHrP and PTH-R1 (Fig. 1D) in selected plasma cell samples, based on the highest cytometric expression.…”

“…(22) The functional role of PTHrP fragments in human pathophysiology has been intensively investigated and their generation by posttranslational proteolysis of members of the subtilisin family, has been definitely assessed. (23)(24)(25) Tumors producing skeletal metastases are usually associated with high PTHrP activity that apparently correlates with poor prognosis in both breast and prostate cancers, (13) although a survival advantage has been unexpectedly described in female patients with lung adenocarcinoma and serum elevation of PTHrP. (26) Nevertheless, the role of PTHrP on cancer growth has been definitely confirmed by demonstrating that its suppression, by either neutralizing antibodies in MDA-MB-231 breast cancer cells or by antisense oligonucleotides in mouse models, restrains tumor progression, resulting in marked reduction of tumor size.…”