Moving Pieces in a Cellular Puzzle: A Cryptic Peptide from the Scorpion Toxin Ts14 Activates AKT and ERK Signaling and Decreases Cardiac Myocyte Contractility via Dephosphorylation of Phospholamban

Cryptic peptides
(cryptides) are biologically active peptides formed
after proteolysis of native precursors present in animal venoms, for
example. Proteolysis is an overlooked post-translational modification
that increases venom complexity. The tripeptide KPP (Lys-Pro-Pro)
is a peptide encrypted in the C-terminus of Ts14a 25-mer peptide
from the venom of the Tityus serrulatus scorpion that has a positive impact on the cardiovascular system,
inducing vasodilation and reducing arterial blood pressure of hypertensive
rats among other beneficial effects. A previous study reported that
KPP and its native peptide Ts14 act via activation of the bradykinin
receptor B2 (B2R). However, the cellular events underlying the activation
of B2R by KPP are unknown. To study the cell signaling triggered by
the Ts14 cryptide KPP, we incubated cardiac myocytes isolated from
C57BL/6 mice with KPP (10–7 mol·L–1) for 0, 5, or 30 min and explored the proteome and phosphoproteome.
Our results showed that KPP regulated cardiomyocyte proteins associated
with, but not limited to, apoptosis, muscle contraction, protein turnover,
and the respiratory chain. We also reported that KPP led to AKT phosphorylation,
activating AKT and its downstream target nitric oxide synthase. We
also observed that KPP led to dephosphorylation of phospholamban (PLN)
at its activation sites (S16 and T17), leading to reduced contractility
of treated cardiomyocytes. Some cellular targets reported here for
KPP (e.g., AKT, PLN, and ERK) have already been reported to protect
the cardiac tissue from hypoxia-induced injury. Hence, this study
suggests potential beneficial effects of this scorpion cryptide that
needs to be further investigated, for example, as a drug lead for
cardiac infarction.

隐蔽肽（Cryptic peptides，简称cryptides）是一类具有生物活性的肽类物质，通常由动物毒液等天然前体蛋白经蛋白水解作用生成。蛋白水解是一种常被忽视的翻译后修饰方式，可提升毒液的复杂度。三肽KPP（即Lys-Pro-Pro）是隐藏在Ts14 C端的肽段：Ts14是取自锯缘栉蝎（Tityus serrulatus）毒液的25肽，对心血管系统具有积极作用，可诱导血管舒张、降低高血压大鼠的动脉血压，同时兼具其他有益生理效应。既往研究表明，KPP及其前体肽Ts14可通过激活缓激肽B2受体（bradykinin receptor B2，B2R）发挥生理作用。然而，KPP激活B2R背后的细胞事件尚未明确。为探究Ts14来源的隐蔽肽KPP所触发的细胞信号通路，我们将从C57BL/6小鼠中分离的心肌细胞以浓度10^-7 mol·L⁻¹的KPP分别孵育0、5或30分钟，随后对其蛋白质组和磷酸化蛋白质组进行分析。研究结果显示，KPP可调控心肌细胞中与细胞凋亡、肌肉收缩、蛋白质周转以及呼吸链相关的蛋白质（不限于上述类别）。我们同时发现，KPP可诱导AKT磷酸化，进而激活AKT及其下游靶标一氧化氮合酶（nitric oxide synthase）。此外，我们观察到KPP可使受磷蛋白（phospholamban，PLN）在其激活位点S16和T17处发生去磷酸化，进而降低处理组心肌细胞的收缩能力。本研究中发现的KPP部分细胞靶点（如AKT、PLN及ERK）此前已有报道可保护心肌组织免受缺氧损伤。因此，本研究表明这类蝎源隐蔽肽具有潜在的有益生理效应，其作为心肌梗死治疗候选药物的开发价值有待进一步探究。