Jang Eun-Ju, Sung Jee Young, Yoo Ha-Eun, Jang Hyonchol, Shim Jaegal, Oh Eok-Soo, Goh Sung-Ho, Kim Yong-Nyun
National Cancer Center, Division of Translational Science, 323 Ilsan-ro, Ilsandong-gu, Gyeonggi-do, Goyang-si 10408, Korea.
Department of Life Sciences, Ewha Womans University, 52, Ewhayeodae-gil, Seodaemun-gu, Seoul 120-750, Korea.
Cancers (Basel). 2021 Jan 11;13(2):247. doi: 10.3390/cancers13020247.
Anoikis is a type of apoptosis induced by cell detachment from the extracellular matrix (ECM), which removes mislocalized cells. Acquisition of anoikis resistance is critical for cancer cells to survive during circulation and, thus, metastasize at a secondary site. Although the sensitization of cancer cells to anoikis is a potential strategy to prevent metastasis, the mechanism underlying anoikis resistance is not well defined. Although family with sequence similarity 188 member B (FAM188B) is predicted as a new deubiquitinase (DUB) member, its biological function has not been fully studied. In this study, we demonstrated that FAM188B knockdown sensitized anoikis of lung cancer cell lines expressing WT-EGFR (A549 and H1299) or TKI-resistant EGFR mutant T790M/L858R (H1975). FAM188B knockdown using si-FAM188B inhibited the growth of all three human lung cancer cell lines cultured in both attachment and suspension conditions. FAM188B knockdown resulted in EGFR downregulation and thus decreased its activity. FAM188B knockdown decreased the activities of several oncogenic proteins downstream of EGFR that are involved in anoikis resistance, including pAkt, pSrc, and pSTAT3, with little changes to their protein levels. Intriguingly, si-FAM188B treatment increased EGFR mRNA levels but decreased its protein levels, which was reversed by treatment with the proteasomal inhibitor MG132, indicating that FAM188B regulates EGFR levels via the proteasomal pathway. In addition, cells transfected with si-FAM188B had decreased expression of FOXM1, an oncogenic transcription factor involved in cell growth and survival. Moreover, FAM188B downregulation reduced metastatic characteristics, such as cell adhesion, invasion, and migration, as well as growth in 3D culture conditions. Finally, tail vein injection of si-FAM188B-treated A549 cells resulted in a decrease in lung metastasis and an increase in mice survival in vivo. Taken together, these findings indicate that FAM188B plays an important role in anoikis resistance and metastatic characteristics by maintaining the levels of various oncogenic proteins and/or their activity, leading to tumor malignancy. Our study suggests FAM188B as a potential target for controlling tumor malignancy.
失巢凋亡是一种由细胞与细胞外基质（ECM）脱离所诱导的细胞凋亡类型，可清除定位错误的细胞。获得失巢凋亡抗性对于癌细胞在循环过程中存活并进而在继发部位转移至关重要。尽管使癌细胞对失巢凋亡敏感是预防转移的一种潜在策略，但失巢凋亡抗性的潜在机制尚未明确。虽然序列相似性家族188成员B（FAM188B）被预测为一种新的去泛素化酶（DUB）成员，但其生物学功能尚未得到充分研究。在本研究中，我们证明FAM188B敲低使表达野生型表皮生长因子受体（WT-EGFR）（A549和H1299）或对酪氨酸激酶抑制剂（TKI）耐药的EGFR突变体T790M/L858R（H1975）的肺癌细胞系对失巢凋亡敏感。使用si-FAM188B敲低FAM188B可抑制在贴壁和悬浮条件下培养的所有三种人肺癌细胞系的生长。FAM188B敲低导致EGFR下调，从而降低其活性。FAM188B敲低降低了EGFR下游几种参与失巢凋亡抗性的致癌蛋白的活性，包括pAkt、pSrc和pSTAT3，而它们的蛋白质水平变化不大。有趣的是，si-FAM188B处理增加了EGFR mRNA水平，但降低了其蛋白质水平，蛋白酶体抑制剂MG132处理可逆转这种情况，表明FAM188B通过蛋白酶体途径调节EGFR水平。此外，用si-FAM188B转染的细胞中，参与细胞生长和存活的致癌转录因子FOXM1的表达降低。此外，FAM188B下调降低了转移特性，如细胞粘附、侵袭和迁移，以及在三维培养条件下的生长。最后，尾静脉注射经si-FAM188B处理的A549细胞导致体内肺转移减少和小鼠存活率增加。综上所述，这些发现表明FAM188B通过维持各种致癌蛋白的水平和/或其活性在失巢凋亡抗性和转移特性中起重要作用，导致肿瘤恶性程度增加。我们的研究表明FAM188B是控制肿瘤恶性程度的潜在靶点。
