Ostrander Julie Hanson, Daniel Andrea R, Lofgren Kristopher, Kleer Celina G, Lange Carol A
Department of Medicine, University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA.
Cancer Res. 2007 May 1;67(9):4199-209. doi: 10.1158/0008-5472.CAN-06-3409.
Total tyrosine kinase activity is often elevated in both cytosolic and membrane fractions of malignant breast tissue and correlates with a decrease in disease-free survival. Breast tumor kinase (Brk; protein tyrosine kinase 6) is a soluble tyrosine kinase that was cloned from a metastatic breast tumor and found to be overexpressed in a majority of breast tumors. Herein, we show that Brk is overexpressed in 86% of invasive ductal breast tumors and coexpressed with ErbB family members in breast cancer cell lines. Additionally, the ErbB ligand, heregulin, activates Brk kinase activity. Knockdown of Brk by stable expression of short hairpin RNA (shRNA) in T47D breast cancer cells decreases proliferation and blocks epidermal growth factor (EGF)- and heregulin-induced activation of Rac GTPase, extracellular signal-regulated kinase (ERK) 5, and p38 mitogen-activated protein kinase (MAPK) but not Akt, ERK1/2, or c-Jun NH(2)-terminal kinase. Furthermore, EGF- and heregulin-induced cyclin D1 expression is dependent on p38 signaling and inhibited by Brk shRNA knockdown. The myocyte enhancer factor 2 transcription factor target of p38 MAPK and ERK5 signaling is also sensitive to altered Brk expression. Finally, heregulin-induced migration of T47D cells requires p38 MAPK activity and is blocked by Brk knockdown. These results place Brk in a novel signaling pathway downstream of ErbB receptors and upstream of Rac, p38 MAPK, and ERK5 and establish the ErbB-Brk-Rac-p38 MAPK pathway as a critical mediator of breast cancer cell migration.
在恶性乳腺组织的胞质和膜部分中，总酪氨酸激酶活性通常会升高，且与无病生存期的缩短相关。乳腺肿瘤激酶（Brk；蛋白酪氨酸激酶6）是一种可溶性酪氨酸激酶，它是从转移性乳腺肿瘤中克隆出来的，发现在大多数乳腺肿瘤中过度表达。在此，我们表明Brk在86%的浸润性导管乳腺癌中过度表达，并在乳腺癌细胞系中与ErbB家族成员共表达。此外，ErbB配体，即神经调节蛋白，可激活Brk激酶活性。通过在T47D乳腺癌细胞中稳定表达短发夹RNA（shRNA）来敲低Brk，可降低细胞增殖，并阻断表皮生长因子（EGF）和神经调节蛋白诱导的Rac GTP酶、细胞外信号调节激酶（ERK）5和p38丝裂原活化蛋白激酶（MAPK）的激活，但不影响Akt、ERK1/2或c-Jun NH(2)-末端激酶。此外，EGF和神经调节蛋白诱导的细胞周期蛋白D1表达依赖于p38信号传导，并受到Brk shRNA敲低的抑制。p38 MAPK和ERK5信号传导的肌细胞增强因子2转录因子靶点对Brk表达的改变也很敏感。最后，神经调节蛋白诱导的T47D细胞迁移需要p38 MAPK活性，并被Brk敲低所阻断。这些结果将Brk置于ErbB受体下游、Rac、p38 MAPK和ERK5上游的一条新的信号通路中，并确立了ErbB-Brk-Rac-p38 MAPK通路是乳腺癌细胞迁移的关键介质。
