Tetranectin在乳癌細胞株MCF-7中所扮演的角色

Abstract

乳癌是全球女性中最常見的癌症種類。尤其近年來由於女性月經初潮提早發生，導致乳癌發病年齡層有年輕化的傾向。此情況不僅在全球，在台灣也有相同的趨勢。因此，乳癌對於婦女健康是ㄧ重大問題而不容忽視。先前研究指出tetranectin (TN)可做為多項人類腫瘤之可靠生物標記，包括乳癌、卵巢癌、口腔癌和膀胱癌…等等。正常情況下，TN在人體血漿中維持一定之濃度。相較於健康者，研究發現罹癌者會出現TN顯著降低的情況，並且又與乳癌患者的病癒存活 (disease-free survivl)及整體存活 (overall survival)有顯著的相關性。低濃度TN則為乳癌轉移的高危險指標，並且在乳腺腫瘤區域胞外基質 (extracellular matrix)表現出更強烈的免疫反應。因此，本研究的目的乃在釐清TN於乳癌細胞株中的功能及其分子機制。 首先，我們於非腫瘤乳腺上皮細胞株MCF10A，三類乳腺癌細胞株 (MCF7、MDA-MB-231和SKBR3)與乳腺導管上皮細胞株BT474中，分別比較TN的蛋白質表現量。結果顯示，在上述之乳癌細胞株中，除MCF10A外，TN皆可在全細胞萃取質 (whole-cell lysates) 和細胞培養液 (conditioned medium)中被偵測到。此外，我們也構築Myc-His-標記 (tagged) TN、TN-綠螢光 (GFP)融合蛋白或去訊息片段 (signal peptide-deficient-)TN-綠螢光之質體DNA載體，再分別將其轉染至MCF7細胞以分析受TN所影響的細胞功能。結果證實於軟洋菜膠 (soft agar)中培養時，全長(full-length) TN皆可增加細胞的非貼附性生長 (anchorage independent growth)，而不影響細胞存活率 (cell viability)。更有甚者，我們亦發現全段TN可顯著增進細胞的活動力 (cell motility)；然而，卻不見於去訊息片段者；此顯示TN於細胞運動中扮演胞外刺激因子的角色。 綜合上述，本研究中發現，TN表現於乳癌細胞株而非正常乳腺上皮細胞中。然而在MCF7細胞株中過量表現TN，可增加細胞活動及非貼附性生長，卻不影響細胞的存活。這些功能上的影響支持TN能在乳腺癌腫瘤的發展中發揮重要作用之假說。至於TN參與腫瘤發展的分子機制仍有待澄清。

Breast cancer is the most common type of cancer in the females worldwide. In recent years, early onset of menarche leads to an increase in the incidence of such cancer in younger woman populations of the world, including Taiwan. Therefore, breast cancer has become a serious health issue for women. Tetranectin (TN) has been found to be a reliable biomarker in certain human carcinoma, including breast cancer, ovary cancer, oral cancer and bladder cancer. Consistently, TN is related to the disease-free and overall survival of breast cancer. Low TN concentrations in human plasma were reported as a high-risk factor for breast cancer metastasis. Interestingly, there has also been shown a strong immunoreactivity in the extracellular matrix associated with breast tumor malignancy. Thus, the purpose of this study was to elucidate the cellular functions of TN and the underlying mechanisms in breast cancer cell line. First, we compared the protein expression of TN in non-tumorigenic epithelial cell line MCF10A, three breast adenocarcinoma cell lines (MCF7, MDA-MB-231 and SKBR3), and the breast ductal carcinoma cell line BT474, and found that TN was detected in both the whole-cell lysates and conditioned media of all breast cancer cell lines, except MCF10A. We then generated the expression constructs of Myc-His-tagged or GFP-fused full-length and signal peptide-deficient TN and transfected each into MCF7 cells to analyze TN-modulated cellular functions. Our results indicate that TN overexpression increased anchorage independent growth in a soft agar assay without affecting cell viability. Interestingly, we also found that TN prominently promoted cell motility, which was not seen for the signal peptide-deficient TN, indicating a role of TN in modulating cell movement is be an extracellular stimulator. In conclusion, we demonstrated in this study that TN is normally up-regulated in breast cancer cell lines, but not in normal breast epithelial cells. When overexpressed, TN increases cell motility and anchorage independent growth in MCF7cell, without affecting cell survival. These support the hypothesis that TN plays an important role in tumor development of breast cancer. Nevertheless, the molecular mechanisms underlying TN-mediated tumor progression remain to be elucidated.