惡性轉移一直是癌症病患的主要死亡原因，而惡性腫瘤的一個重要特徵便是其具有抗失巢凋亡的能力而在非貼附性的環境中仍可繼續生長。在過去的研究中指出，表皮生長因子受體（EGFR）訊息路徑的異常活化可導致腫瘤細胞產生對於失巢凋亡的抗性而在癌症轉移的過程中扮演著重要的角色。而在最近的研究中發現，人類膜內絲胺酸蛋白酶 RHBDL2 可藉由裂解表皮生長因子 （EGF）刺激 EGFR 路徑的活化，此外在我們過去的研究中也發現過度表現 RHBDL2 的 HaCaT 細胞具有較快的生長速度及較佳的移行能力，這些結果顯示出 RHBDL2 的作用或許涉及在癌症的惡性轉移過程中。經由進一步檢視不同腫瘤細胞株中 RHBDL2 的表現情形，只有 HeLa S3 與 MDA-MB-231 這二株細胞在懸浮性的培養環境中仍可持續高度表現 RHBDL2。其中，較惡性的 HeLa S3 細胞以懸浮性條件培養時，可觀察到RHBDL2 的高度表現及 ERK 的持續磷酸化，而相對較良性的 HeLa 細胞則無此現象。此外，不論是利用 shRNA 抑制 RHBDL2 的表現量或是加入絲胺酸蛋白酶抑制劑 3,4-dichloroisocoumarin ，都可明顯的抑制 HeLa S3 細胞在懸浮性培養環境中的生長能力。接著我們進一步檢視 EGFR 訊息路徑對於 HeLa S3抗失巢凋亡能力的影響，結果顯示出抑制 EGFR 的作用會減弱 HeLa S3 對於失巢凋亡的抗性；而相對的，刺激 EGFR 的活化則可增強 HeLa 細胞在非貼附性培養環境中的生存能力。綜合這些結果，我們認為 RHBDL2 在與 EGFR 相關的抗失巢凋亡作用中扮演著重要的角色。

Metastasis is the major cause of mortality in cancer patients, the hallmark features of metastatic cancer are anoikis resistance and anchorage-independent growth. Previous studies have shown that signaling through the epidermal growth factor receptor (EGFR) may confer resistance to anoikis and play a pivotal role in tumor metastasis. Recently, it has been suggested that an intramembrane serine protease RHBDL2 (rhomboid-like 2) activates EGFR by releasing epidermal growth factor (EGF). Additionally, in our previous studies, we found that RHBDL2 overexpressed HaCaT cells exhibited higher migratory ability and proliferation rate. The results suggest that RHBDL2 may be involved in metastasis. By investigating the expression of RHBDL2 in tumor cells, we found that the mRNA and protein levels of RHBDL2 were significantly elevated in human tumor cells, such as HeLa and MDA-MB-231, under non-attachment culture condition. The suspension-cultured malignant HeLa S3 cells but not HeLa, expressed persistently high levels of RHBDL2 and phosphorylated extracellular signal-regulated kinase (p-ERK). Furthermore, either shRNA knockdown of RHBDL2 or treatment with 3,4-dichloroisocoumarin, a serine protease inhibitor, suppressed the growth of suspended HeLa S3 cells. Moreover, we survey the effect of EGFR signalling in anoikis-resistant ability of HeLa S3 cells. The results show that EGFR inhibition attenuated the ability of anoikis-resistance of HeLa S3 cells. In contrast, activation of EGFR appears to promote the viability of HeLa cells under non-attachment culture condition. Taken together, our results suggest that RHBDL2 may play a pivotal role in EGFR-mediated anoikis resistance of tumor cells.

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