IQGAP1 is a multidomain cancer-associated protein that serves as a scaffold protein for multiple signaling pathways. Numerous binding partners have been found for the calponin homology, IQ and GAP-related domains in IQGAP1. Identification of a binding partner for its WW domain has proven elusive, however, even though a cell-penetrating peptide derived from this domain has marked anti-tumor activity. Here, using in vitro binding assays with human proteins and co-precipitation from human cells, we show that the WW domain of human IQGAP1 binds directly to the p110α catalytic subunit of phosphoinositide 3-kinase (PI3K). In contrast, the WW domain does not bind to ERK1/2, MEK1/2, or the p85α regulatory subunit of PI3K when p85α is expressed alone. However, the WW domain is able to bind to the p110α/p85α heterodimer when both subunits are co-expressed, as well as to the mutationally activated p110α/p65α heterodimer. We present a model of the structure of the IQGAP1 WW domain, and experimentally identify key residues in the hydrophobic core and beta strands of the WW domain that are required for binding to p110α. These findings contribute to a more precise understanding of IQGAP1-mediated scaffolding, and of how IQGAP1-derived therapeutic peptides might inhibit tumorigenesis.

中文翻译：

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IQGAP1 的 WW 结构域直接与 PI 3 激酶的 p110α 催化亚基结合

IQGAP1 是一种多结构域癌症相关蛋白，可作为多种信号通路的支架蛋白。IQGAP1 中的钙调蛋白同源性、IQ 和 GAP 相关结构域有许多结合伴侣。然而，尽管源自该结构域的细胞穿透肽具有显着的抗肿瘤活性，但其 WW 结构域的结合伴侣的鉴定已被证明难以捉摸。在这里，利用人类蛋白质的体外结合测定和人类细胞的共沉淀，我们表明人类 IQGAP1 的 WW 结构域直接与磷酸肌醇 3 激酶 (PI3K) 的 p110α 催化亚基结合。相反，当 p85α 单独表达时，WW 结构域不与 ERK1/2、MEK1/2 或 PI3K 的 p85α 调节亚基结合。然而，当两个亚基共表达时，WW 结构域能够结合 p110α/p85α 异二聚体，以及突变激活的 p110α/p65α 异二聚体。我们提出了 IQGAP1 WW 结构域的结构模型，并通过实验鉴定了 WW 结构域的疏水核心和 β 链中与 p110α 结合所需的关键残基。这些发现有助于更准确地理解 IQGAP1 介导的支架，以及 IQGAP1 衍生的治疗肽如何抑制肿瘤发生。