Seales Eric C, Jurado Gustavo A, Brunson Brian A, Wakefield John K, Frost Andra R, Bellis Susan L
Department of Pathology, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Cancer Res. 2005 Jun 1;65(11):4645-52. doi: 10.1158/0008-5472.CAN-04-3117.
Colon adenocarcinomas are known to express elevated levels of alpha2-6 sialylation and increased activity of ST6Gal-I, the Golgi glycosyltransferase that creates alpha2-6 linkages. Elevated ST6Gal-I positively correlates with metastasis and poor survival, and therefore ST6Gal-I-mediated hypersialylation likely plays a role in colorectal tumor invasion. Previously we found that oncogenic ras (present in roughly 50% of colon adenocarcinomas) up-regulates ST6Gal-I and, in turn, increases sialylation of beta1 integrin adhesion receptors in colon epithelial cells. However, we wanted to know if this pattern held true in vivo and, if so, how beta1 hypersialylation might contribute to colon tumor progression. In the present study, we find that beta1 integrins from colon adenocarcinomas consistently carry higher levels of alpha2-6 sialic acid. To explore the effects of increased alpha2-6 sialylation on beta1-integrin function, we stably expressed ST6Gal-I in a colon epithelial cell line lacking endogenous ST6Gal-I. ST6Gal-I expressors (with alpha2-6 sialylated beta1 integrins) exhibited up-regulated attachment to collagen I and laminin and increased haptotactic migration toward collagen I, relative to parental cells (with completely unsialylated beta1 integrins). Blockade of ST6Gal-I expression with short interfering RNA reversed collagen binding back to the level of ST6Gal-I nonexpressors, confirming that alpha2-6 sialylation regulates beta1 integrin function. Finally, we show that beta1 integrins from ST6Gal-I expressors have increased association with talin, a marker for integrin activation. Collectively, these findings suggest that beta1 hypersialylation may augment colon tumor progression by altering cell preference for certain extracellular matrix milieus, as well as by stimulating cell migration.
已知结肠腺癌表达高水平的α2-6唾液酸化，且ST6Gal-I（一种可形成α2-6连接的高尔基体糖基转移酶）的活性增加。ST6Gal-I水平升高与转移和不良预后呈正相关，因此ST6Gal-I介导的高唾液酸化可能在结直肠癌侵袭中起作用。此前我们发现，致癌性Ras（约50%的结肠腺癌中存在）上调ST6Gal-I，进而增加结肠上皮细胞中β1整合素黏附受体的唾液酸化。然而，我们想知道这种模式在体内是否成立，如果成立，β1高唾液酸化如何促进结肠肿瘤进展。在本研究中，我们发现结肠腺癌中的β1整合素始终携带更高水平的α2-6唾液酸。为了探究α2-6唾液酸化增加对β1整合素功能的影响，我们在缺乏内源性ST6Gal-I的结肠上皮细胞系中稳定表达ST6Gal-I。相对于亲代细胞（β1整合素完全未唾液酸化），ST6Gal-I表达细胞（β1整合素α2-6唾液酸化）对I型胶原和层粘连蛋白的黏附上调，且对I型胶原的趋触性迁移增加。用小干扰RNA阻断ST6Gal-I表达可使胶原结合恢复到非表达ST6Gal-I细胞的水平，证实α2-6唾液酸化调节β1整合素功能。最后，我们表明来自ST6Gal-I表达细胞的β1整合素与踝蛋白（一种整合素激活标志物）的结合增加。总体而言，这些发现表明β1高唾液酸化可能通过改变细胞对某些细胞外基质环境的偏好以及刺激细胞迁移来促进结肠肿瘤进展。
