Bardwell A Jane, Paul Madhuri, Yoneda Kiku C, Andrade-Ludeña María D, Nguyen Oanh T, Fruman David, Bardwell Lee
University of California Irvine, Irvine, California, United States.
University of California Irvine, Irvine, United States.
Biochem J. 2023 May 5. doi: 10.1042/BCJ20220493.
IQGAP1 is a multi-domain 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.
IQGAP1是一种与癌症相关的多结构域蛋白，作为多种信号通路的支架蛋白。已发现IQGAP1中钙调蛋白同源结构域、IQ结构域和GAP相关结构域有众多结合伴侣。然而，尽管源自该结构域的一种细胞穿透肽具有显著的抗肿瘤活性，但其WW结构域的结合伴侣却难以确定。在此，我们通过对人类蛋白质进行体外结合试验以及从人类细胞中共沉淀，发现人类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。相比之下，当单独表达p85α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结构域能够与p110α/p85α异二聚体结合，也能与突变激活的p110α/p65α异二聚体结合。我们提出了IQGAP1 WW结构域的结构模型，并通过实验确定了WW结构域疏水核心和β链中与p110α结合所需的关键残基。这些发现有助于更精确地理解IQGAP1介导的支架作用，以及IQGAP1衍生的治疗性肽如何抑制肿瘤发生。
