Department of Gastrointestinal Surgery and Department of Medical Oncology, the Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, 510655, China.
Guangdong Institute of Gastroenterology, Guangdong Provincial Key Laboratory of Colorectal and Pelvic Floor Diseases, the Sixth Affiliated Hospital, Sun Yat-Sen University, Guangzhou, 510655, China.
J Transl Med. 2023 Jun 19;21(1):399. doi: 10.1186/s12967-023-04156-w.
Bone marrow metastasis (BMM) is underestimated in gastric cancer (GC). GC with BMM frequently complicate critical hematological abnormalities like diffused intravascular coagulation and microangiopathic hemolytic anemia, which constitute a highly aggressive GC (HAGC) subtype. HAGC present a very poor prognosis with peculiar clinical and pathological features when compared with not otherwise specified advanced GC (NAGC). But the molecular mechanisms underlying BMM from GC remain rudimentary.
The transcriptomic difference between HAGC and NAGC were analyzed. Genes that were specifically upregulated in HAGC were identified, and their effect on cell migration and invasion was studied. The function of ACTN2 gene were confirmed by GC cell lines, bone-metastatic animal model and patients' tissues. Furthermore, the molecular mechanism of ACTN2 derived-BMM was explored by multiple immunofluorescence staining, western blot, chromatin immunoprecipitation, and luciferase reporter assays.
We elucidated the key mechanisms of BMM depending on the transcriptomic difference between HAGC and NAGC. Five genes specifically upregulated in HAGC were assessed their effect on cell migration and invasion. The ACTN2 gene encoding protein α-Actinin-2 was detected enhanced the metastatic capability and induced BMM of GC cells in mouse models. Mechanically, α-Actinin-2 was involved in filopodia formation where it promoted the Actin filament cross-linking by replacing α-Actinin-1 to form α-Actinin-2:α-Actinin-4 complexes in GC cells. Moreover, NF-κB subunit RelA and α-Actinin-2 formed heterotrimers in the nuclei of GC cells. As a direct target of RelA:α-Actinin-2 heterotrimers, the ACTN2 gene was a positive auto-regulatory loop for α-Actinin-2 expression.
We demonstrated a link between filopodia, BMM and ACTN2 activation, where a feedforward activation loop between ACTN2 and RelA is established via actin in response to distant metastasis. Given the novel filopodia formation function and the new mechanism of BMM in GC, we propose ACTN2 as a druggable molecular vulnerability that may provide potential therapeutic benefit against BMM of GC.
骨髓转移（BMM）在胃癌（GC）中被低估。伴有 BMM 的 GC 常伴有弥漫性血管内凝血和微血管溶血性贫血等严重的血液学异常，这些异常构成了一种高度侵袭性的 GC（HAGC）亚型。与非特指晚期 GC（NAGC）相比，HAGC 的预后非常差，且具有独特的临床和病理特征。但 GC 中 BMM 的分子机制仍很基础。
分析 HAGC 和 NAGC 之间的转录组差异。鉴定在 HAGC 中特异性上调的基因，并研究其对细胞迁移和侵袭的影响。通过 GC 细胞系、骨转移动物模型和患者组织证实 ACTN2 基因的功能。此外，通过多重免疫荧光染色、Western blot、染色质免疫沉淀和荧光素酶报告基因检测等方法探讨了 ACTN2 衍生的 BMM 的分子机制。
我们阐明了依赖于 HAGC 和 NAGC 转录组差异的 BMM 的关键机制。评估了在 HAGC 中特异性上调的五个基因对细胞迁移和侵袭的影响。编码蛋白α-Actinin-2 的 ACTN2 基因被检测到增强了 GC 细胞在小鼠模型中的转移能力并诱导了 BMM。在机制上，α-Actinin-2 参与了微丝的形成，在 GC 细胞中通过取代α-Actinin-1 形成α-Actinin-2:α-Actinin-4 复合物来促进肌动蛋白丝交联。此外，NF-κB 亚基 RelA 和 α-Actinin-2 在 GC 细胞的核内形成异三聚体。作为 RelA:α-Actinin-2 异三聚体的直接靶标，ACTN2 基因是α-Actinin-2 表达的正反馈自动调节环。
我们证明了微丝、BMM 和 ACTN2 激活之间存在联系，其中 ACTN2 和 RelA 之间建立了一个前馈激活环，通过肌动蛋白对远处转移做出反应。鉴于 ACTN2 在 GC 中具有新的微丝形成功能和 BMM 的新机制，我们提出 ACTN2 是一种可药物治疗的分子弱点，可能为 GC 的 BMM 提供潜在的治疗益处。
