Annexin A6 (AnxA6), a member of the calcium (Ca²⁺) and membrane binding annexins, is known to stabilize and establish the formation of multifactorial signaling complexes. At the plasma membrane, AnxA6 is a scaffold for protein kinase Cα (PKCα) and GTPase‐activating protein p120GAP to promote downregulation of epidermal growth factor receptor (EGFR) and Ras/mitogen‐activated protein kinase (MAPK) signaling. In human squamous A431 epithelial carcinoma cells, which overexpress EGFR, but lack endogenous AnxA6, restoration of AnxA6 expression (A431‐A6) promotes PKCα‐mediated threonine 654 (T654)–EGFR phosphorylation, which inhibits EGFR tyrosine kinase activity. This is associated with reduced A431‐A6 cell growth, but also decreased migration and invasion in wound healing, matrigel, and organotypic matrices. Here, we show that A431‐A6 cells display reduced EGFR activity in vivo , with xenograft analysis identifying increased pT654‐EGFR levels, but reduced tyrosine EGFR phosphorylation compared to controls. In contrast, PKCα depletion in A431‐A6 tumors is associated with strongly reduced pT654 EGFR levels, yet increased EGFR tyrosine phosphorylation and MAPK activity. Moreover, tyrosine kinase inhibitors (TKIs; gefitinib, erlotinib) more effectively inhibit cell viability, clonogenic growth, and wound healing of A431‐A6 cells compared to controls. Likewise, the ability of AnxA6 to inhibit A431 motility and invasiveness strongly improves TKI efficacy in matrigel invasion assays. This correlates with a greatly reduced invasion of the surrounding matrix of TKI‐treated A431‐A6 when cultured in 3D spheroids. Altogether, these findings implicate that elevated AnxA6 scaffold levels contribute to improve TKI‐mediated inhibition of growth and migration, but also invasive properties in EGFR overexpressing human squamous epithelial carcinoma.

中文翻译：

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Annexin A6改善了过表达EGFR的人类鳞状上皮细胞中酪氨酸激酶抑制剂的抗迁移和抗侵袭特性。

膜联蛋白A6（AnxA6），钙（Ca ²⁺）和膜结合膜联蛋白，已知稳定并建立多因子信号复合物的形成。在质膜上，AnxA6是蛋白激酶Cα（PKCα）和GTPase激活蛋白p120GAP的支架，可促进表皮生长因子受体（EGFR）和Ras /促分裂原激活蛋白激酶（MAPK）信号的下调。在过度表达EGFR但缺乏内源性AnxA6的人鳞状上皮A431癌细胞中，AnxA6表达的恢复（A431-A6）促进了PKCα介导的苏氨酸654（T654）-EGFR磷酸化，从而抑制了EGFR酪氨酸激酶活性。这与减少A431-A6细胞的生长有关，但也减少了伤口愈合，基质胶和器官型基质中的迁移和侵袭。在这里，我们显示A431‐A6细胞显示出降低的EGFR活性体内 ，通过异种移植分析确定与对照组相比，pT654-EGFR水平升高，但酪氨酸EGFR磷酸化水平降低。相比之下，A431-A6肿瘤中的PKCα耗竭与pT654 EGFR水平显着降低，但EGFR酪氨酸磷酸化和MAPK活性增加有关。此外，与对照组相比，酪氨酸激酶抑制剂（TKIs；吉非替尼，厄洛替尼）更有效地抑制A431-A6细胞的细胞活力，克隆生长和伤口愈合。同样，在基质胶侵袭试验中，AnxA6抑制A431活力和侵袭性的能力极大地提高了TKI效力。在3D椭球体中培养时，这与TKI处理过的A431-A6周围基质的侵袭大大减少有关。共，