Gonzalez Maria E, Peterson Esther A, Privette Lisa M, Loffreda-Wren Janice L, Kalikin Linda M, Petty Elizabeth M
Departments of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109, USA.
Cancer Res. 2007 Sep 15;67(18):8554-64. doi: 10.1158/0008-5472.CAN-07-1474.
Altered expression of the human septin gene, SEPT9, and its murine homologue, Sept9, has been implicated in neoplasia. However, their role(s) in oncogenesis remains poorly understood. We found amplification of SEPT9 in 67% of breast cancer cells (BCC) when compared with immortalized human mammary epithelial cells (IHMEC) as well as high levels of SEPT9 expression in the majority (61%) of the BCCs studied, unlike IHMECs. Expression profiling of variant SEPT9 transcripts and translated products revealed that high expression of the variant, SEPT9_v1, in contrast to other variants, was widespread in BCCs (55% of the BCCs) but not in IHMECs. High expression of SEPT9_v1 was also observed in primary breast cancer samples by immunohistochemical studies. We subsequently examined the phenotypic consequences of SEPT9_v1 expression in human breast cells. Retroviral expression of SEPT9_v1 in IHMEC cell culture models showed that SEPT9_v1 accelerated growth kinetics, stimulated cell motility, promoted invasion in Matrigel Transwell assays, increased genomic instability with the development of aneuploidy, and stimulated morphologic changes. Significant cytokinesis defects and disruption of tubulin microfilaments were also observed by immunofluorescence when SEPT9_v1 was ectopically expressed in IHMECs. Furthermore, SEPT9_v1 markedly enhanced neoplastic transformation in Hs578T cells, a BCC with no endogenous expression of the SEPT9_v1 isoform. Small interfering RNA-mediated and short hairpin RNA-mediated inhibition of SEPT9_v1 expression in two BCCs with high levels of endogenous SEPT9_v1 expression inhibited neoplastic growth properties of the cells. Taken together, our findings suggest that increased SEPT9_v1 expression contributes to the malignant pathogenesis of some breast tumors.
人类septin基因SEPT9及其小鼠同源物Sept9的表达改变与肿瘤形成有关。然而，它们在肿瘤发生中的作用仍知之甚少。与永生化人乳腺上皮细胞（IHMEC）相比，我们发现67%的乳腺癌细胞（BCC）中存在SEPT9扩增，并且在所研究的大多数（61%）BCC中SEPT9表达水平较高，这与IHMEC不同。变异型SEPT9转录本和翻译产物的表达谱分析表明，与其他变异型相比，变异型SEPT9_v1的高表达在BCC中广泛存在（占BCC的55%），但在IHMEC中不存在。免疫组织化学研究也在原发性乳腺癌样本中观察到SEPT9_v1的高表达。我们随后研究了SEPT9_v1在人乳腺细胞中表达的表型后果。在IHMEC细胞培养模型中，SEPT9_v1的逆转录病毒表达表明，SEPT9_v1加速了生长动力学，刺激了细胞运动，在基质胶Transwell实验中促进了侵袭，随着非整倍体的出现增加了基因组不稳定性，并刺激了形态学变化。当SEPT9_v1在IHMEC中异位表达时，免疫荧光也观察到明显的胞质分裂缺陷和微管微丝的破坏。此外，SEPT9_v1显著增强了Hs578T细胞中的肿瘤转化，Hs578T细胞是一种内源性不表达SEPT9_v1亚型的BCC。在两个内源性SEPT9_v1表达水平高的BCC中，小干扰RNA介导和短发夹RNA介导的SEPT9_v1表达抑制抑制了细胞的肿瘤生长特性。综上所述，我们的研究结果表明，SEPT9_v1表达增加有助于某些乳腺肿瘤的恶性发病机制。
