Department of Oral and Maxillofacial Surgery, Okayama University Graduate School of Medicine, Dentistry, and Pharmaceutical Sciences, Okayama, Japan.
Anticancer Res. 2010 Dec;30(12):5029-36.
Breast cancer (BC) cells often metastasize to bone where they express large amounts of parathyroid hormone-related protein (PTHrP). In this study, we investigated the possibility that PTHrP may have roles in breast cancer bone metastasis independently of, or in addition to, its roles in osteoclastic function.
A mouse model of bone metastasis was prepared by inoculating mice with suspensions of the human BC cell line MDA-MB-231 tumor cells via the left cardiac ventricle. Matrix metalloproteinase-13 (MMP-13) expression in the bone microenvironment was examined by Western blot and Real-time RT-PCR (RT-PCR) analysis, as well as by confocal microscopy.
The invading MDA-MB-231 cells contained conspicuous amounts of both PTHrP and MMP-13, an important matrix-degrading enzyme; and treatment of the cells in culture with exogenous PTHrP markedly stimulated MMP13 gene expression. Analysis of signaling mechanisms showed that PTHrP treatment led to rapid increases in the levels of phosphorylated protein kinase C (PKCα) and extracellular signal-regulated kinase (ERK1/2). Pharmacologic inhibition of ERK1/2 and PKC as well as of PKA activities counteracted the PTHrP-dependent stimulation of MMP13 expression. Indeed, pharmacologic activation of PKA or PKC was sufficient for stimulation of MMP13 expression.
Consistent with these findings, the inhibition of PKC prevented PTHrP-induced activation of ERK1/2, whereas 12-O-tetradecanoylphorbol-13-acetate (TPA), a stimulator of PKC, up-regulated the PTHrP-induced activation of ERK1/2. Taken together, our data indicate that the MDA-MB-231 breast cancer cells may carry out bone destruction and favor their own metastatic behavior by producing MMP-13. Given that the cells expressed PTHrP and that this factor stimulated MMP-13 expression, metastatic bone destruction may result from a PTHrP autocrine loop involving a PKC-ERK1/2 signaling pathway.
乳腺癌（BC）细胞常转移至骨骼，在骨骼中大量表达甲状旁腺激素相关蛋白（PTHrP）。在这项研究中，我们研究了 PTHrP 可能在骨转移中的作用，该作用可能独立于或除了其在破骨细胞功能中的作用以外。
通过将人乳腺癌细胞系 MDA-MB-231 肿瘤细胞悬液经左心室接种到小鼠中，制备骨转移模型。通过 Western blot 和实时 RT-PCR（RT-PCR）分析以及共聚焦显微镜检查，研究骨微环境中的基质金属蛋白酶-13（MMP-13）的表达。
侵袭性 MDA-MB-231 细胞含有大量的 PTHrP 和 MMP-13，后者是一种重要的基质降解酶；并且细胞培养物中外源 PTHrP 的处理显著刺激了 MMP13 基因的表达。对信号机制的分析表明，PTHrP 处理导致磷酸化蛋白激酶 C（PKCα）和细胞外信号调节激酶（ERK1/2）水平的迅速增加。ERK1/2 和 PKC 以及 PKA 活性的药理学抑制作用拮抗了 PTHrP 依赖性的 MMP13 表达刺激。实际上，PKA 或 PKC 的药理学激活足以刺激 MMP13 表达。
与这些发现一致，PKC 的抑制作用阻止了 PTHrP 诱导的 ERK1/2 激活，而 12-O-十四烷酰佛波醇-13-乙酸酯（TPA），PKC 的刺激物，上调了 PTHrP 诱导的 ERK1/2 激活。总之，我们的数据表明，MDA-MB-231 乳腺癌细胞可能通过产生 MMP-13 来破坏骨骼并促进其自身的转移行为。鉴于细胞表达 PTHrP，并且该因子刺激 MMP-13 表达，转移性骨破坏可能是由于涉及 PKC-ERK1/2 信号通路的 PTHrP 自分泌环引起的。
