Abstract：
The Shoc2 scaffold protein is crucial in transmitting signals within the Epidermal Growth Factor Receptor (EGFR)-mediated Extracellular signal-Regulated Kinase (ERK1/2) pathway. While the significance of Shoc2 in this pathway is well-established, the precise mechanisms through which Shoc2 governs signal transmission remain to be fully elucidated. Hereditary variants in Shoc2 are responsible for Noonan Syndrome with Loose anagen Hair (NSLH). However, due to the absence of known enzymatic activity in Shoc2, directly assessing how these variants affect its function is challenging. ERK1/2 phosphorylation is used as a primary parameter of Shoc2 function, but the impact of Shoc2 mutants on the pathway activation is unclear. This study investigates how the NSLH-associated Shoc2 variants influence EGFR signals in the context of the ERK1/2 and AKT downstream signaling pathways. We show that when the ERK1/2 pathway is a primary signaling pathway activated downstream of EGFR, Shoc2 variants cannot upregulate ERK1/2 phosphorylation to the level of the WT Shoc2. Yet, when the AKT and ERK1/2 pathways were activated, in cells expressing Shoc2 variants, ERK1/2 phosphorylation was higher than in cells expressing WT Shoc2. In cells expressing the Shoc2 NSLH mutants, we found that the AKT signaling pathway triggers the PAK activation, followed by phosphorylation of Raf-1/MEK1/2 and activation of the ERK1/2 signaling axis. Hence, our studies reveal a previously unrecognized feedback regulation downstream of the EGFR and provide additional evidence for the role of Shoc2 as a \"gatekeeper\" in controlling the selection of downstream effectors within the EGFR signaling network.
摘要：
Shoc2支架蛋白在传递表皮生长因子受体（EGFR）介导的细胞外信号调节激酶（ERK1/2）途径内的信号中至关重要。虽然Shoc2在这一途径中的重要性已得到证实，Shoc2控制信号传输的精确机制仍有待充分阐明。Shoc2中的遗传变异体是具有松散毛发的Noonan综合征(NSLH)的原因。然而,由于Shoc2中缺乏已知的酶活性,直接评估这些变体如何影响其功能是具有挑战性的。ERK1/2磷酸化被用作Shoc2功能的主要参数，但Shoc2突变体对通路激活的影响尚不清楚。这项研究调查了NSLH相关的Shoc2变体如何在ERK1/2和AKT下游信号通路的背景下影响EGFR信号。我们发现，当ERK1/2通路是EGFR下游激活的主要信号通路时，Shoc2变体不能将ERK1/2磷酸化上调至WTShoc2的水平。然而，当AKT和ERK1/2通路被激活时，在表达Shoc2变体的细胞中，ERK1/2磷酸化高于表达WTShoc2的细胞。在表达Shoc2NSLH突变体的细胞中，我们发现AKT信号通路触发了PAK的激活,随后是Raf-1/MEK1/2的磷酸化和ERK1/2信号轴的激活。因此，我们的研究揭示了以前未被认识到的EGFR下游的反馈调节,并为Shoc2作为"看门人"在控制EGFR信号网络中下游效应物选择方面的作用提供了更多证据.
