oxytocin and Osteosarcoma

Oxytocin stimulates proliferation of human osteoblast-like (hOB) cells and human osteosarcoma cells (SaOS-2). In contrast, oxytocin has also been shown to inhibit proliferation of other cell lines such as breast cancer cells. The aim of the present study was to investigate the effects of different concentrations of oxytocin on cell proliferation in osteosarcoma cell lines of different stages of differentiation: SaOS-2, TE-85, and UMR-106. For this purpose cells were incubated with oxytocin (1-1000 pmol/l). Cell proliferation was measured by [(3)H]thymidine incorporation and a commercially available kit (EZ4U). Incubation with oxytocin during 24 h increased proliferation of SaOS-2 cells significantly (100 pmol/l: p<0.01). In contrast, 24 h of incubation with oxytocin decreased proliferation of TE-85 (100 pmol/l: p<0.01) and UMR-106 cells significantly (100 pmol/l: p<0.01). The effects of oxytocin in SaOS-2 and TE-85, but not in UMR-106 cells, were abolished when the cells were incubated with both oxytocin and an oxytocin antagonist (1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin). Instead incubation with the oxytocin antagonist alone decreased proliferation of UMR-106 cells significantly (p<0.001). Thus oxytocin has the capacity to both stimulate and inhibit cell proliferation of osteosarcoma cells. This effect might be dependent on the stage of differentiation of the cancer cells.

Topics: Cell Line, Tumor; Cell Proliferation; Dose-Response Relationship, Drug; Hormone Antagonists; Humans; Osteosarcoma; Oxytocin; Time Factors; Vasotocin

Two inbred rat lines have been developed that show either high (HAB) or low (LAB) anxiety-related behavior. The behavioral phenotype correlates with arginine vasopressin (AVP) expression at the level of the hypothalamic paraventricular nucleus (PVN), but not supraoptic nucleus, with HAB animals overexpressing the neuropeptide in both magnocellular and parvocellular subdivisions of the PVN. We detected a number of single nucleotide polymorphisms (SNPs) in the AVP locus that differ between the HAB and LAB animals, two of which were embedded in cis-regulatory elements. The HAB-specific allele of the AVP gene promoter occurs in 1.5% of outbred Wistar rats and is more transcriptionally active in vivo, as revealed by allele-specific transcription studies in cross-mated HAB/LAB F1 animals. Interestingly, one specific SNP [A(-1276)G] conferred reduced binding of the transcriptional repressor CArG binding factor A (CBF-A) in the HAB allele, the consequent differential regulation of the AVP promoter resulting in an overexpression of AVP in vitro and in vivo. Furthermore, CBF-A is highly coexpressed in AVP-containing neurons of the PVN supporting an important role for regulation of AVP gene expression in vivo. Taken together, our results demonstrate a role for an AVP gene polymorphism and CBF-A in elevated AVP expression in the PVN of HAB rats likely to contribute to their behavioral and neuroendocrine phenotype.

Topics: Alleles; Animals; Anxiety; Arginine Vasopressin; Bone Neoplasms; Cell Cycle Proteins; Cell Line, Tumor; DNA-Binding Proteins; DNA, Single-Stranded; Exploratory Behavior; Fear; Gene Expression Regulation; Heterogeneous-Nuclear Ribonucleoprotein Group A-B; Humans; Inbreeding; Maze Learning; Osteosarcoma; Oxytocin; Paraventricular Hypothalamic Nucleus; Polymorphism, Single Nucleotide; Promoter Regions, Genetic; Protein Binding; Protein Interaction Mapping; Rats; Rats, Wistar; Reaction Time; Recombinant Fusion Proteins; Repressor Proteins; Ribonucleoproteins; Transcription Factors; Transcription, Genetic; Transfection

We have previously described the presence of the functional plasminogen activator system on the surfaces of bone neoplastic cells and the fact that plasmin specifically cleaves bone matrix protein osteocalcin (OC). The cleavage of OC to NH2-midterminal (1-44) and COOH-terminal RFYGPV hexapeptide (44-49) proceeds with detachment of both products from bone mineral. Because the sequence of OC-derived hexapeptide (HP) is nearly identical to the E2 region of the oxytocin receptor (OTR), we set out to ascertain whether the HP interferes with the osteosarcoma (OS)-associated oxytocin (OT) system. We documented the presence and functional activity of OTRs in several OS cells by means of (a) OT-mediated inhibition of OS growth; (b) expression of OTR mRNA by means of reverse transcription-PCR; (c) immunofluorescence staining with IF3 monoclonal antibody specific for human OTR; and (d) saturation binding and Scatchard analysis of OT binding to the receptors of isolated membranes or intact OS cells. Although we could not demonstrate direct binding of HP to OT, the presence of HP in cultures of OS cells antagonizes the inhibitory effect of OT on these cells. Additionally, in competitive binding assays, the HP effectively competes with binding of OT to its cognate receptors. The results indicate the existence of an OTR/OT system in tumor cells of bone origin. Suggested plasminogen activator-OC-OTR/OT interactions may have an effect on the regulation of cell proliferation within the bone tissue as well as properties of the extracellular matrix surrounding the tumor foci in the bone.

Topics: Amino Acid Sequence; Bone Neoplasms; Cell Division; Cell Membrane; Consensus Sequence; Fibrinolysin; Humans; Kinetics; Models, Biological; Models, Molecular; Osteocalcin; Osteosarcoma; Oxytocin; Peptide Fragments; Protein Structure, Secondary; Receptors, Oxytocin; Reverse Transcriptase Polymerase Chain Reaction; Tumor Cells, Cultured