Epidermal growth factor receptor (EGFR) remains the sole druggable molecular target other than the PD1/PD-L1 pathway with meaningful clinical benefit in squamous cell carcinoma of head and neck (SCCHN). Human epidermal growth factor receptor 3 (HER3) confers the resistance to EGFR-targeted treatment in SCCHN. Thus, it is essential to determine the distribution and regulatory mechanisms of HER3 in SCCHN. We explored the prevalence of HER3 expression and its distribution within SCCHN by immunohistochemical staining and clinicopathological correlations were analyzed. The regulatory mechanism of HER3 expression was then dissected in vitro, using RT-PCR, Western blotting, and immunoprecipitation in a set of SCCHN cell lines. Subsequent in vivo validation in the murine model was also performed. We found that concomitant high expression of HER3 and its ligand NRG1 in SCCHN is associated with the increased presence of regional lymphatic metastasis and the majority of HER3 is located on the differentiated tumor cells. Further investigation revealed that HER3 is under positive control of NOTCH1 through transcriptional activation and inhibition of protein degradation through the polyubiquitination machinery via AKT pathway and USP8 deubiquitinating enzyme. In addition, loss of function of NOTCH1 suppresses HER3 expression through increased phosphorylation of serine 473 of AKT in SCCHN cells, and promotes the aggressiveness of the tumor cells. These data indicated that the level of HER3 is regulated by NOTCH1 in SCCHN both transcriptionally and post-translationally, and NOTCH1 is in a higher hierarchy in the regulatory system of the AKT pathway. Since NOTCH1 is inactivated in approximately 10% of SCCHN cases and this aberration strongly impacts the AKT pathway and diminishes HER3, exclusion of patients with NOTCH1-inactivated SCCHN may be beneficial for future clinical trials of HER3-targeting antibodies.

表皮生长因子受体 (EGFR) 仍然是除 PD1/PD-L1 通路之外的唯一可药物分子靶标，在头颈部鳞状细胞癌 (SCCHN) 中具有有意义的临床益处。人表皮生长因子受体 3 (HER3) 在 SCCHN 中赋予对 EGFR 靶向治疗的抗性。因此，确定 HER3 在 SCCHN 中的分布和调节机制至关重要。我们通过免疫组织化学染色探索了 HER3 表达的普遍性及其在 SCCHN 中的分布，并分析了临床病理学相关性。然后在一组 SCCHN 细胞系中使用 RT-PCR、蛋白质印迹和免疫沉淀在体外剖析 HER3 表达的调节机制。还在小鼠模型中进行了随后的体内验证。我们发现 SCCHN 中 HER3 及其配体 NRG1 的伴随高表达与区域淋巴转移的存在增加有关，并且大部分 HER3 位于分化的肿瘤细胞上。进一步的研究表明，HER3 通过转录激活和通过多泛素化机制通过 AKT 途径和 USP8 去泛素化酶抑制蛋白质降解，处于 NOTCH1 的阳性控制之下。此外，NOTCH1功能的丧失通过增加SCCHN细胞中AKT丝氨酸473的磷酸化来抑制HER3表达，并促进肿瘤细胞的侵袭性。这些数据表明 HER3 的水平受 SCCHN 中 NOTCH1 的转录和翻译后调节，NOTCH1 在 AKT 通路的调控系统中处于更高的层次。由于大约 10% 的 SCCHN 病例中 NOTCH1 失活，并且这种畸变强烈影响 AKT 通路并减少 HER3，因此排除具有 NOTCH1 失活 SCCHN 的患者可能有益于未来针对 HER3 靶向抗体的临床试验。