Two human osteoblast-like osteosarcoma cell lines show distinct expression and differential regulation of parathyroid hormone-related protein

Roles of Parathyroid Hormone-Related Protein (PTHrP) and Its Receptor (PTHR1) in Normal and Tumor Tissues: Focus on Their Roles in Osteosarcoma

Osteosarcoma (OS) is the most common primary bone tumor and originates from bone forming mesenchymal cells and primarily affects children and adolescents. The 5-year survival rate for OS is 60 to 65%, with little improvement in prognosis during the last four decades. Studies have demonstrated the evolving roles of parathyroid hormone-related protein (PTHrP) and its receptor (PTHR1) in bone formation, bone remodeling, regulation of calcium transport from blood to milk, regulation of maternal calcium transport to the fetus and reabsorption of calcium in kidneys. These two molecules also play critical roles in the development, progression and metastasis of several tumors such as breast cancer, lung carcinoma, chondrosarcoma, squamous cell carcinoma, melanoma and OS. The protein expression of both PTHrP and PTHR1 have been demonstrated in OS, and their functions and proposed signaling pathways have been investigated yet their roles in OS have not been fully elucidated. This review aims to discuss the latest research with PTHrP and PTHR1 in OS tumorigenesis and possible mechanistic pathways.

This review is dedicated to Professor Michael Day who died in May 2020 and was a very generous collaborator.

Parathyroid hormone/parathyroid hormone-related peptide regulate osteosarcoma cell functions: Focus on the extracellular matrix (Review)

Osteosarcoma (OS) is a primary bone tumor of mesenchymal origin mostly affecting children and adolescents. The OS extracellular matrix (ECM) is extensively altered as compared to physiological bone tissue. Indeed, the main characteristic of the most common osteoblastic subtype of OS is non-mineralized osteoid production. Parathyroid hormone (PTH) is a polypeptide hormone secreted by the chief cells of the parathyroid glands. The PTH-related peptide (PTHrP) may be comprised of 139, 141 or 173 amino acids and exhibits considerate N-terminal amino acid sequence homology with PTH. The function of PTH/PTHrP is executed through the activation of the PTH receptor 1 (PTHR1) and respective downstream intracellular pathways which regulate skeletal development, bone turnover and mineral ion homeostasis. Both PTHR1 and its PTH/PTHrP ligands have been shown to be expressed in OS and to affect the functions of these tumor cells. This review aims to highlight the less well known aspects of PTH/PTHrP functions in the progression of OS by focusing on ECM-dependent signaling.

Cloning and sequencing of the 3'-region of the canine parathyroid hormone-related protein gene and analysis of alternate mRNA splicing in two canine carcinomas

A canine genomic library in Lambda FIX II vector was screened with a 281-base pair canine PTHrP cDNA to the prepro- and coding regions. Two genomic clones were isolated and mapped to the 3'-end of the PTHrP gene by polymerase chain reaction (PCR) amplification of exons in this region. One clone (3.5 kb) was amplified by PCR, partially sequenced, and compared to the human PTHrP gene. Regions were identified with a high degree of homology to exons 6, 7, and 8 of the human PTHrP gene. A polyadenylation site was present 3' to the exon 8-like region. Reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated that exon 7 of the PTHrP gene was transcribed in two canine carcinomas (SCC 2/88 cells and CAC-8 tumor line) which produce PTHrP. This confirmed that the 3'-region of the canine PTHrP gene is alternately spliced with splicing of exon 6 to exons 7 or 9. Transcription of exon 8 was not demonstrated by RT-PCR and suggests that the exon 8-like region of the dog PTHrP gene is not utilized. The exon 8-like region contained an early stop codon that was not present in exon 8 of the human PTHrP gene.