琥珀醯輔酶A合成酶 (Succinyl-coenzyme A synthetase，又稱Succinate-CoA Ligase)是三羧酸循環 (tricarboxylic acid cycle)中的關鍵酵素，其代謝途徑參與著電子傳遞鏈(electron transport chain)及丙酸代謝路徑 (propanoate metabolism)。琥珀醯輔酶A連接酶是一種異二聚體，由α亞基及β亞基所構成。α亞基編碼的基因為SUCLG1，功能是將琥珀醯輔酶A轉化為琥珀酸。β亞基由SUCLA2及SUCLG2所編碼，不同的β亞基可以决定酶對ADP或GDP的特異性。為了研究SUCLA2在不同癌症中的表達程度，利用大型資料庫分析SUCLA2與癌症的關聯性。在cBioPortal資料庫分析結果表明，基因sucla2在大多數癌症中呈現缺失。同時，SUCLA2之mRNA表現程度在乳癌中相較於正常乳腺組織呈現下調趨勢。此外，Prognoscan資料庫顯示在癌症中SUCLA2的低表達對病人有較差的預後。以上資訊表明了SUCLA2在癌症中扮演著抑癌基因的角色。然而，目前研究對於SUCLA2在乳癌發展的相關作用機制尚未明瞭。在本篇研究中，使用RNAi技術構建了一個穩定抑制SUCLA2的乳癌細胞株 (BT474及MDA-MB-231)。並透過實驗分析其細胞型態，生長，爬行等相關機能性測試。與對照細胞相比，SUCLA2基因靜默之細胞株在細胞生長、群落形成及細胞攤開能力有顯著的提升，這表明SUCLA2基因靜默促進了乳癌細胞的侵襲和擴散。透過MTT測定細胞內粒線體的琥珀酸脫氫酶 (Succinate dehydrogenase, SDH)活性，結果呈現其活性下降，並發現在纖連蛋白下細胞貼附能力之改變。在西方墨點法分析結果呈現抑制SUCLA2表達之細胞株上調了細胞內糖解蛋白GLUT3、HK1和HK2的表達，且改變了EMT蛋白表現程度。總而言之，以上實驗結果證實了SUCLA2對於乳癌之惡性程度扮演重要角色。此研究連結了乳癌與抑制內源性SUCLA2表達對於癌症惡性程度之分析。

Succinyl coenzyme A synthetase (SCS, also called succinate-CoA ligase) is a critical enzyme in TCA cycle and participates in propanoate metabolism and metabolic pathways. The enzyme reversibly converts succinyl-CoA into succinate. Succinate-CoA ligase is a heterodimer that consists of α and β subunits. The β subunit is encoded by either SUCLG2 or SUCLA2, which determines the enzyme specificity for either GDP or ADP. SUCLA2 accompanied with the substrate-level phosphorylation of ADP to ATP is highly expressed in brain, muscle and heart. In order to study the expression of SUCLA2 in a variety of cancers, we used mega database to analyze the relationship between SUCLA2 and cancer. Analysis of the cBioPortal database showed that sucla2 gene was deleted in most of cancers. Also, SUCLA2 level was down-regulated in breast cancer. In addition, the Prognoscan database revealed that low SUCLA2 expression level in breast cancer had a poor prognosis. However, the function of SUCLA2 in breast cancer development is still unknown. In this study, we used the RNAi technique to construct a stable cell line of the SUCLA2 knockdown in breast cancer cells (BT474 and MDA-MB-231). Compared to the control cells, SUCLA2 knockdown cells had a significant effect on cell growth, colony formation, cell-spreading and cell adhesion ability, which means knockdown SUCLA2 promoted the cell invasion and migration. MTT assay showed knockdown SUCLA2 decreased the succinate dehydrogenase activity in breast cancer cells. In western blot, knockdown SUCLA2 cells up-regulated GLUT3, HK1 and HK2 expression, indicating the glycolysis function was increased. Knockdown SUCLA2 cells also changed the protein expression level of EMT marker. In conclusion, knockdown of SUCLA2 expression increased the tumor progression in breast cancer. This study contributes new insight into the role of SUCLA2 in breast cancer development.

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