Hyaluronan (HA) is a ubiquitous extracellular matrix component playing a crucial role in the regulation of cell behaviors, including cancer. Aggressive breast cancer cells tend to proliferate, migrate and metastatize. Notably, triple-negative breast cancer cells lacking the expression of estrogen receptor (ER) as well as progesterone receptor and HER2 are more aggressive than ER-positive ones. As currently no targeted therapy is available for triple-negative breast cancer, the identification of novel therapeutic targets has a high clinical priority. In ER-negative cells, tumoral behavior can be reduced by inhibiting HA synthesis or silencing the enzymes involved in its metabolism, such as HA synthase 2 (HAS2). HAS2-AS1 is a long non-coding RNA belonging to the natural antisense transcript family which is known to favor HAS2 gene expression and HA synthesis, thus bolstering malignant progression in brain, ovary, and lung tumors. As the role of HAS2-AS1 has not yet been investigated in breast cancer, in this work we report that ER-positive breast cancers had lower HAS2-AS1 expression compared to ER-negative tumors. Moreover, the survival of patients with ER-negative tumors was higher when the expression of HAS2-AS1 was elevated. Experiments with ER-negative cell lines as MDA-MB-231 and Hs 578T revealed that the overexpression of either the full-length HAS2-AS1 or its exon 2 long or short isoforms alone, strongly reduced cell viability, migration, and invasion, whereas HAS2-AS1 silencing increased cell aggressiveness. Unexpectedly, in these ER-negative cell lines, HAS2-AS1 is involved neither in the regulation of HAS2 nor in HA deposition. Finally, transcriptome analysis revealed that HAS2-AS1 modulation affected several pathways, including apoptosis, proliferation, motility, adhesion, epithelial to mesenchymal transition, and signaling, describing this long non-coding RNA as an important regulator of breast cancer cells aggressiveness.

透明质酸 (HA) 是一种普遍存在的细胞外基质成分，在调节细胞行为（包括癌症）中起着至关重要的作用。侵袭性乳腺癌细胞倾向于增殖、迁移和转移。值得注意的是，缺乏雌激素受体 (ER) 以及孕激素受体和 HER2 表达的三阴性乳腺癌细胞比 ER 阳性细胞更具侵袭性。由于目前还没有针对三阴性乳腺癌的靶向治疗，因此确定新的治疗靶点具有很高的临床优先级。在 ER 阴性细胞中，可以通过抑制 HA 合成或沉默参与其代谢的酶，如 HA 合酶 2 (HAS2) 来减少肿瘤行为。HAS2-AS1 是一种长链非编码 RNA，属于天然反义转录物家族，已知有利于 HAS2 基因表达和 HA 合成，从而促进脑、卵巢和肺肿瘤的恶性进展。由于尚未研究 HAS2-AS1 在乳腺癌中的作用，在这项工作中，我们报告 ER 阳性乳腺癌与 ER 阴性肿瘤相比具有较低的 HAS2-AS1 表达。此外，当 HAS2-AS1 表达升高时，ER 阴性肿瘤患者的存活率更高。用 MDA-MB-231 和 Hs 578T 等 ER 阴性细胞系进行的实验表明，全长 HAS2-AS1 或其外显子 2 长或短同种型单独过表达，强烈降低细胞活力、迁移和侵袭，而HAS2-AS1 沉默增加了细胞的攻击性。不料，在这些 ER 阴性细胞系中，HAS2-AS1 既不参与 HAS2 的调节，也不参与 HA 的沉积。最后，转录组分析显示，HAS2-AS1 调节影响了多种途径，包括细胞凋亡、增殖、运动、粘附、上皮间质转化和信号传导，将这种长链非编码 RNA 描述为乳腺癌细胞侵袭性的重要调节因子。