ABSTRACT
A clonal cell line (Saos-2/B-10) derived from human osteosarcoma Saos-2 cells had the same osteoblastic characteristics as the mother line, but lacked sensitivity to parathyroid hormone (PTH) at early passages. At later passages (> 70) the cells became very sensitive to PTH (0·1 nmol/l). The absence of PTH-stimulatable adenylate cyclase correlated with the secretion of an adenylate cyclase-stimulatory activity which had the properties of the recently characterized PTH-like peptide (PTH-LP). This activity was inhibited by the PTH antagonist [8norleucyl, 18norleucyl, 34tyrosinyl]bovine PTH-(3–34)amide and could be neutralized by an antiserum raised against the synthetic PTH-LP-(1–34). Hybridization with a human PTH-LP cDNA showed that these cells produce two PTH-LP mRNAs of approximately 1·5 and 1·8 kb. The production of PTH-LP was stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA; 150 nmol/l) and epidermal growth factor (EGF; 10 ng/ml). The increased accumulation of PTH-LP in conditioned media in response to TPA was seen after 1 h and levelled off at 6 h. In contrast, EGF stimulation was lower at 3 and 6 h but continued for 24 h. Both agents increased PTH-LP mRNA levels in Saos-2/B-10 cells. A TPA analogue which does not stimulate protein kinase C had no effect on PTH-LP production. Cycloheximide blocked the stimulatory effect of both TPA and EGF and the TPA effect was blocked by actinomycin D, suggesting transcriptional control. The regulation of PTH-LP by these agents may offer clues regarding the association of this protein with malignancy.
Journal of Endocrinology (1989) 122, 219–227
Macropinocytic entry of isolated mitochondria in epidermal growth factor-activated human osteosarcoma cells