Introduction

Acral melanoma is a predominant and aggressive subtype of melanoma in non-Caucasian populations. There is a lack of genotype-driven therapies for over 50% of patients. TRPM1 (transient receptor potential melastatin 1), a nonspecific cation channel, is mainly expressed in retinal bipolar neurons and skin. Nonetheless, the function of TRPM1 in melanoma progression is poorly understood.

Objectives

We investigated the association between TRPM1 and acral melanoma progression and revealed the molecular mechanisms by which TRPM1 promotes tumor progression and malignancy.

Methods

TRPM1 expression and CaMKII phosphorylation in tumor specimens were tested by immunohistochemistry analysis and scored by two independent investigators. The functions of TRPM1 and CaMKII were assessed using loss-of-function and gain-of-function approaches and examined by western blotting, colony formation, cell migration and invasion, and xenograft tumor growth assays. The effects of a CaMKII inhibitor, KN93, were evaluated using both in vitro cell and in vivo xenograft mouse models.

Results

We revealed that TRPM1 protein expression was positively associated with tumor progression and shorter survival in patients with acral melanoma. TRPM1 promoted AKT activation and the colony formation, cell mobility, and xenograft tumor growth of melanoma cells. TRPM1 elevated cytosolic Ca²⁺ levels and activated CaMKIIδ (Ca²⁺/calmodulin-dependent protein kinase IIδ) to promote the CaMKIIδ/AKT interaction and AKT activation. The functions of TRPM1 in melanoma cells were suppressed by a CaMKII inhibitor, KN93. Significant upregulation of phospho-CaMKII levels in acral melanomas was related to increased expression of TRPM1. An acral melanoma cell line with high expression of TRPM1, CA11, was isolated from a patient to show the anti-tumor activity of KN93 in vitro and in vivo.

Conclusions

TRPM1 promotes tumor progression and malignancy in acral melanoma by activating the Ca^2+/CaMKIIδ/AKT pathway. CaMKII inhibition may be a potential therapeutic strategy for treating acral melanomas with high expression of TRPM1.

中文翻译：

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TRPM1 通过激活 Ca2+/CaMKIIδ/AKT 通路促进肢端黑色素瘤的肿瘤进展

 介绍

肢端黑色素瘤是非白种人群体中一种主要且具有侵袭性的黑色素瘤亚型。超过 50% 的患者缺乏基因型驱动的治疗方法。 TRPM1（瞬态受体电位melastatin 1）是一种非特异性阳离子通道，主要表达于视网膜双极神经元和皮肤。尽管如此，TRPM1 在黑色素瘤进展中的功能仍知之甚少。

 目标

我们研究了 TRPM1 与肢端黑色素瘤进展之间的关联，并揭示了 TRPM1 促进肿瘤进展和恶性肿瘤的分子机制。

 方法

通过免疫组织化学分析检测肿瘤标本中的 TRPM1 表达和 CaMKII 磷酸化，并由两名独立研究人员进行评分。使用功能丧失和功能获得方法评估 TRPM1 和 CaMKII 的功能，并通过蛋白质印迹、集落形成、细胞迁移和侵袭以及异种移植肿瘤生长测定进行检查。使用体外细胞和体内异种移植小鼠模型评估了 CaMKII 抑制剂 KN93 的作用。

 结果

我们发现 TRPM1 蛋白表达与肢端黑色素瘤患者的肿瘤进展和较短的生存期呈正相关。 TRPM1 促进 AKT 激活以及黑色素瘤细胞的集落形成、细胞迁移和异种移植肿瘤生长。 TRPM1 升高胞质 Ca ²⁺水平并激活 CaMKIIδ（Ca ²⁺ /钙调蛋白依赖性蛋白激酶 IIδ）以促进 CaMKIIδ/AKT 相互作用和 AKT 激活。黑色素瘤细胞中 TRPM1 的功能被 CaMKII 抑制剂 KN93 抑制。肢端黑色素瘤中磷酸 CaMKII 水平的显着上调与 TRPM1 表达增加有关。从患者体内分离出高表达 TRPM1 的肢端黑色素瘤细胞系 CA11，以显示 KN93 的体外和体内抗肿瘤活性。

 结论

TRPM1 通过激活 Ca ^2+/ CaMKIIδ/AKT 通路促进肢端黑色素瘤的肿瘤进展和恶性。 CaMKII 抑制可能是治疗高表达 TRPM1 的肢端黑色素瘤的潜在治疗策略。