Menendez Javier A, Rubio Miguel A, Campisi Judith, Lupu Ruth
ProCURE (Program Against Cancer Therapeutic Resistance), Metabolism & Cancer Group, Catalan Institute of Oncology (ICO), Girona, Spain.
Girona Biomedical Research Institute (IDIBGI), Girona, Spain.
Oncotarget. 2015 Nov 24;6(37):39422-36. doi: 10.18632/oncotarget.4964.
The growth factor heregulin (HRG) promotes breast cancer (BC) tumorigenesis and metastasis and differentially modulates BC cell responses to DNA-damaging agents via its dual extracellular and nuclear localization. Given the central role of telomere dysfunction to drive carcinogenesis and to alter the chemotherapeutic profile of transformed cells, we hypothesized that an unanticipated nuclear function of HRG might be to regulate telomere length. Engineered overexpression of the HRGβ2 isoform in non-aggressive, HRG-negative MCF-7 BC cells resulted in a significant shortening of telomeres (up to 1.3 kb) as measured by Southern blotting of telomere terminal restriction fragments. Conversely, antisense-mediated suppression of HRGβ2 in highly aggressive, HRG-overexpressing MDA-MB-231 and Hs578T cells increased telomere length up to 3.0 kb. HRGβ2 overexpression promoted a marked upregulation of telomere-binding protein 2 (TRF2) protein expression, whereas its knockdown profoundly decreased TRF2 expression. Double staining of endogenous HRGβ2 with telomere-specific peptide nucleic acid probe/fluorescence in situ hybridization (PNA/FISH) revealed the partial localization of HRG at the chromosome ends. Moreover, a predominantly nucleoplasmic staining pattern of endogenous HRGβ2 appeared to co-localize with TRF2 and, concomitantly with RAP1, a telomere regulator that specifically interacts with TRF2. Small interfering RNA-mediated knockdown of HRG decreased the expression of TRF2 and RAP1, decreased their presence at chromosome ends, and coincidentally resulted in the formation of longer telomeres. This study uncovers a new function for HRGβ2 in controlling telomere length, in part due to its ability to regulate and interact with the telomere-associated proteins TRF2 and RAP1.
这里的生长因子神经调节蛋白（HRG）可促进乳腺癌（BC）的肿瘤发生和转移，并通过其细胞外和细胞核的双重定位差异调节BC细胞对DNA损伤剂的反应。鉴于端粒功能障碍在驱动致癌作用以及改变转化细胞的化疗特征方面的核心作用，我们推测HRG一个未被预料到的核功能可能是调节端粒长度。在侵袭性较弱、HRG阴性的MCF-7 BC细胞中通过基因工程过表达HRGβ2亚型，通过端粒末端限制片段的Southern印迹法检测发现端粒显著缩短（达1.3 kb）。相反，在高侵袭性、HRG过表达的MDA-MB-231和Hs578T细胞中，通过反义介导抑制HRGβ2可使端粒长度增加达3.0 kb。HRGβ2过表达促进了端粒结合蛋白2（TRF2）蛋白表达的显著上调，而敲低其表达则使TRF2表达大幅下降。用端粒特异性肽核酸探针/荧光原位杂交（PNA/FISH）对内源性HRGβ2进行双重染色，显示HRG部分定位于染色体末端。此外，内源性HRGβ2主要的核质染色模式似乎与TRF2共定位，并且与RAP1（一种特异性与TRF2相互作用的端粒调节因子）同时存在。小干扰RNA介导的HRG敲低降低了TRF2和RAP1的表达，减少了它们在染色体末端的存在，并同时导致形成更长的端粒。本研究揭示了HRGβ2在控制端粒长度方面的新功能，部分原因是其调节端粒相关蛋白TRF2和RAP1以及与之相互作用的能力。
