Wali Vikram B, Gilmore-Hebert Maureen, Mamillapalli Ramanaiah, Haskins Jonathan W, Kurppa Kari J, Elenius Klaus, Booth Carmen J, Stern David F
Department of Pathology, Yale School of Medicine, P.O.Box 208023, New Haven, CT, 06520, USA.
Department of Breast Medical Oncology, Yale Cancer Center, Room#786, 300 George Street, New Haven, CT-06511, USA.
Breast Cancer Res. 2014 Dec 17;16(6):501. doi: 10.1186/s13058-014-0501-z.
Human Epidermal Growth Factor Receptor (ERBB4/HER4) belongs to the Epidermal Growth Factor receptor/ERBB family of receptor tyrosine kinases. While ERBB1, ERBB2 and ERBB3 are often overexpressed or activated in breast cancer, and are oncogenic, the role of ERBB4 in breast cancer is uncertain. Some studies suggest a tumor suppressor role of ERBB4, while other reports suggest an oncogenic potential. Alternative splicing of ERBB4 yields four major protein products, these spliced isoforms differ in the extracellular juxtamembrane domain (JM-a versus JM-b) and cytoplasmic domain (CYT-1 versus CYT-2). Two of these isoforms, JM-a CYT-1 and JM-a CYT-2, are expressed in the mammary gland. Failure to account for isoform-specific functions in previous studies may account for conflicting reports on the role of ERBB4 in breast cancer.
We have produced mouse mammary tumour virus (MMTV) -ERBB4 transgenic mice to evaluate potential developmental and carcinogenic changes associated with full length (FL) JM-a ERBB4 CYT-1 versus ERBB4 CYT-2. Mammary tissue was isolated from transgenic mice and sibling controls at various developmental stages for whole mount analysis, RNA extraction, and immunohistochemistry. To maintain maximal ERBB4 expression, transgenic mice were bred continuously for a year after which mammary glands were isolated and analyzed.
Overexpressing FL CYT-1 isoform resulted in suppression of mammary ductal morphogenesis which was accompanied by decreased number of mammary terminal end buds (TEBs) and Ki-67 positive cells within TEBs, while FL CYT-2 isoform had no effect on ductal growth in pubescent mice. The suppressive ductal phenotype in CYT-1 mice disappeared after mid-pregnancy, and subsequent developmental stages showed no abnormality in mammary gland morphology or function in CYT-1 or CYT-2 transgenic mice. However, sustained expression of FL CYT-1 isoform resulted in formation of neoplastic mammary lesions, suggesting a potential oncogenic function for this isoform.
Together, we present isoform-specific roles of ERBB4 during puberty and early pregnancy, and reveal a novel oncogenic property of CYT-1 ERBB4. The results may be exploited to develop better therapeutic strategies in breast cancer.
人表皮生长因子受体（ERBB4/HER4）属于受体酪氨酸激酶的表皮生长因子受体/ERBB家族。虽然ERBB1、ERBB2和ERBB3在乳腺癌中常过度表达或被激活，具有致癌性，但ERBB4在乳腺癌中的作用尚不确定。一些研究表明ERBB4具有肿瘤抑制作用，而其他报告则提示其具有致癌潜力。ERBB4的可变剪接产生四种主要蛋白质产物，这些剪接异构体在细胞外近膜结构域（JM-a与JM-b）和细胞质结构域（CYT-1与CYT-2）存在差异。其中两种异构体，JM-a CYT-1和JM-a CYT-2，在乳腺中表达。以往研究未能考虑异构体特异性功能，可能是关于ERBB4在乳腺癌中作用的报道相互矛盾的原因。
我们构建了小鼠乳腺肿瘤病毒（MMTV）-ERBB4转基因小鼠，以评估与全长（FL）JM-a ERBB4 CYT-1和ERBB4 CYT-2相关的潜在发育和致癌变化。在不同发育阶段从转基因小鼠及其同窝对照中分离乳腺组织，用于整体分析、RNA提取和免疫组织化学。为维持最大程度的ERBB4表达，转基因小鼠连续繁殖一年，之后分离并分析乳腺。
过表达FL CYT-1异构体导致乳腺导管形态发生受到抑制，同时乳腺终末芽（TEB）数量减少，TEB内Ki-67阳性细胞数量减少，而FL CYT-2异构体对青春期小鼠的导管生长没有影响。CYT-1小鼠的抑制性导管表型在妊娠中期后消失，随后的发育阶段，CYT-1或CYT-2转基因小鼠的乳腺形态或功能均未显示异常。然而，FL CYT-1异构体的持续表达导致乳腺肿瘤性病变形成，提示该异构体具有潜在致癌功能。
我们共同展示了ERBB4在青春期和妊娠早期的异构体特异性作用，并揭示了CYT-1 ERBB4的一种新的致癌特性。这些结果可用于开发更好的乳腺癌治疗策略。
