Jackson J, Meisinger J, Patel S, Lim Z C, Vellody K, Metz R, Young M R
Research Services, Hines V.A. Hospital, Hines, Ill., USA.
Invasion Metastasis. 1997;17(4):199-209.
Metastatic Lewis lung carcinoma (LLC-LN7) variants have previously been shown to have reduced levels of protein phosphatase-2A (PP-2A) activity as compared to the nonmetastatic LLC-C8 cells. The present study showed that inhibition of PP-2A in the nonmetastatic LLC-C8 cells caused a rapid change from a spread to a rounded morphology and increased their in vitro invasiveness through laminin. In contrast, the metastatic LLC-LN7 cells were rounded and invasive, which was not affected by inhibition of PP-2A. To determine whether these differences could be attributed to alterations in PP-2A association with the cytoskeleton, the extent of PP-2A colocalization with microtubules was tested. Immunostaining for tubulin showed prominent filamentous fibers in nonmetastatic LLC-C8 cells and small foci of PP-2A immunostaining along these microtubules. In contrast, the tubulin staining was diffuse throughout the metastatic LLC-LN7 cells and there was little evidence of association with PP-2A. Western blot analyses showed that this reduced level of PP-2A association with microtubules in metastatic LLC-LN7 cells was not due to differences in levels of the PP-2A subunits. Instead, it may be due to the reduced association of the subunits into the heterotrimeric form of the PP-2A holoenzyme. These studies show the importance of PP-2A in maintaining a spread morphology and in restricting invasiveness, and a loss of this regulatory control in metastatic cells. This loss of PP-2A regulatory control in metastatic cells may be due to a reduction in the trimeric form of the PP-2A holoenzyme.
与非转移性LLC - C8细胞相比，转移性Lewis肺癌（LLC - LN7）变体先前已显示出蛋白磷酸酶2A（PP - 2A）活性水平降低。本研究表明，抑制非转移性LLC - C8细胞中的PP - 2A会导致细胞形态迅速从铺展变为圆形，并增加其通过层粘连蛋白的体外侵袭性。相反，转移性LLC - LN7细胞呈圆形且具有侵袭性，PP - 2A的抑制对此没有影响。为了确定这些差异是否可归因于PP - 2A与细胞骨架结合的改变，测试了PP - 2A与微管共定位的程度。微管蛋白免疫染色显示非转移性LLC - C8细胞中有突出的丝状纤维，并且沿着这些微管有小的PP - 2A免疫染色灶。相反，微管蛋白染色在转移性LLC - LN7细胞中呈弥漫性，几乎没有与PP - 2A结合的证据。蛋白质印迹分析表明，转移性LLC - LN7细胞中PP - 2A与微管结合水平的降低不是由于PP - 2A亚基水平的差异。相反，这可能是由于亚基结合形成PP - 2A全酶异源三聚体的减少。这些研究表明PP - 2A在维持铺展形态和限制侵袭性方面的重要性，以及转移性细胞中这种调节控制的丧失。转移性细胞中PP - 2A调节控制的丧失可能是由于PP - 2A全酶三聚体形式的减少。
