Perkel V S, Mohan S, Herring S J, Baylink D J, Linkhart T A
Department of Medicine, Loma Linda University, California.
Cancer Res. 1990 Nov 1;50(21):6902-7.
Prostatic cancer typically produces osteoblastic metastases which are not attended by marrow fibrosis (i.e., osteoblast but not stromal fibroblast proliferation). In the present study we sought to test the hypothesis that prostatic cancer cells produce factor(s) which act selectively on human osteoblasts. Such a paracrine mechanism would explain the observed increase in osteoblasts, unaccompanied by an increase in marrow fibroblasts. To test this hypothesis we investigated the mitogenic activity released by the human prostatic tumor cell line, PC3. PC3 cells have been reported previously to produce mitogenic activity for cells that was relatively specific for rat osteoblasts compared to rat fibroblasts. However, the effects of this activity on human cells has not been examined previously. PC3-conditioned medium (CM) (5-50 micrograms CM protein/ml) stimulated human osteoblast proliferation by 200-950% yet did not stimulate human fibroblast proliferation [( 3H]thymidine incorporation). PC3 CM also increased cell numbers in human osteoblast but not fibroblast cell cultures. To determine whether the osteoblast-specific mitogenic activity could be attributed to known bone growth factors, specific assays for these growth factors were performed. PC3 CM contained 10 pg insulin-like growth factor (IGF) I, less than 2 pg IGF II, 54 pg basic fibroblast growth factor, and 16 pg transforming growth factor beta/microgram CM protein. None of these growth factors alone or in combination could account for the observed osteoblast-specific PC3 cell-derived mitogenic activity. Furthermore, when 5 micrograms/ml PC3 CM was tested in combination with maximally effective concentrations of either basic fibroblast growth factor, IGF I, IGF II, or transforming growth factor beta, it produced an additive effect suggesting that PC3 CM stimulates osteoblast proliferation by a mechanism independent of these bone mitogens. Biochemical characterization supported the hypothesis that the PC3 cell growth factor was unique from other growth factors. The PC3 growth factor did not bind to heparin and was resistant to acid as well as the reducing agent, dithiothreitol. Sephadex G-75 and fast protein liquid chromatography Mono S cation-exchange chromatography revealed the PC3-derived mitogen to be an Mr 26,000-30,000 basic protein. Therefore, we conclude that PC3 cells release a mitogen which exhibits higher specificity for human osteoblasts than human fibroblasts and is unique from other growth factors tested. Production of this mitogen by human prostatic carcinoma cells could play an etiological role in the intense osteoblast-specific stimulation that occurs at sites of bone metastases.
前列腺癌通常产生成骨性转移灶，且无骨髓纤维化（即有成骨细胞但无基质成纤维细胞增殖）。在本研究中，我们试图验证前列腺癌细胞产生的因子能选择性作用于人类成骨细胞这一假说。这样一种旁分泌机制可以解释所观察到的成骨细胞增加，而骨髓成纤维细胞却未增加的现象。为验证这一假说，我们研究了人前列腺肿瘤细胞系PC3释放的促有丝分裂活性。此前有报道称，PC3细胞能产生对细胞具有促有丝分裂活性，与大鼠成纤维细胞相比，该活性对大鼠成骨细胞相对具有特异性。然而，此前尚未研究过这种活性对人类细胞的影响。PC3条件培养基（CM）（5 - 50微克CM蛋白/毫升）能刺激人类成骨细胞增殖200 - 950%，但不刺激人类成纤维细胞增殖（[³H]胸腺嘧啶核苷掺入）。PC3 CM也能增加人类成骨细胞培养物中的细胞数量，但对成纤维细胞培养物无此作用。为确定成骨细胞特异性促有丝分裂活性是否可归因于已知的骨生长因子，我们对这些生长因子进行了特异性检测。PC3 CM含有10皮克胰岛素样生长因子（IGF）I、少于2皮克IGF II、54皮克碱性成纤维细胞生长因子以及16皮克转化生长因子β/微克CM蛋白。这些生长因子单独或联合使用均无法解释所观察到的PC3细胞来源的成骨细胞特异性促有丝分裂活性。此外，当5微克/毫升的PC3 CM与最大有效浓度的碱性成纤维细胞生长因子、IGF I、IGF II或转化生长因子β联合检测时，产生了相加效应，这表明PC3 CM通过一种独立于这些骨有丝分裂原的机制刺激成骨细胞增殖。生化特性支持了PC3细胞生长因子不同于其他生长因子这一假说。PC3生长因子不与肝素结合且对酸以及还原剂二硫苏糖醇具有抗性。葡聚糖G - 75和快速蛋白质液相色谱单S阳离子交换色谱显示，PC3来源的有丝分裂原是一种分子量为26,000 - 30,000的碱性蛋白。因此，我们得出结论，PC3细胞释放一种对人类成骨细胞比对人类成纤维细胞具有更高特异性的有丝分裂原，且不同于所检测的其他生长因子。人类前列腺癌细胞产生这种有丝分裂原可能在骨转移部位发生的强烈成骨细胞特异性刺激中起病因学作用。
