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Isolated p110a subunit of PI3Ka provides a platform for structure-based drug design
Structural highlights
DiseasePK3CA_HUMAN Note=Most of the cancer-derived mutations are missense mutations and map to one of the three hotspots: Glu-542; Glu-545 and His-1047. Mutated isoforms participate in cellular transformation and tumorigenesis induced by oncogenic receptor tyrosine kinases (RTKs) and HRAS1/KRAS. Interaction with HRAS1/KRAS is required for Ras-driven tumor formation. Mutations increasing the lipid kinase activity are required for oncogenic signaling. The protein kinase activity may not be required for tumorigenesis. Defects in PIK3CA are associated with colorectal cancer (CRC) [MIM:114500. Defects in PIK3CA are a cause of susceptibility to breast cancer (BC) [MIM:114480. A common malignancy originating from breast epithelial tissue. Breast neoplasms can be distinguished by their histologic pattern. Invasive ductal carcinoma is by far the most common type. Breast cancer is etiologically and genetically heterogeneous. Important genetic factors have been indicated by familial occurrence and bilateral involvement. Mutations at more than one locus can be involved in different families or even in the same case. Defects in PIK3CA are a cause of susceptibility to ovarian cancer (OC) [MIM:167000. Ovarian cancer common malignancy originating from ovarian tissue. Although many histologic types of ovarian neoplasms have been described, epithelial ovarian carcinoma is the most common form. Ovarian cancers are often asymptomatic and the recognized signs and symptoms, even of late-stage disease, are vague. Consequently, most patients are diagnosed with advanced disease. Defects in PIK3CA may underlie hepatocellular carcinoma (HCC) [MIM:114550.[1] Defects in PIK3CA are a cause of keratosis seborrheic (KERSEB) [MIM:182000. A common benign skin tumor. Seborrheic keratoses usually begin with the appearance of one or more sharply defined, light brown, flat macules. The lesions may be sparse or numerous. As they initially grow, they develop a velvety to finely verrucous surface, followed by an uneven warty surface with multiple plugged follicles and a dull or lackluster appearance.[2] Defects in PIK3CA are the cause of congenital lipomatous overgrowth, vascular malformations, and epidermal nevi (CLOVE) [MIM:612918. CLOVE is a sporadically occurring, non-hereditary disorder characterized by asymmetric somatic hypertrophy and anomalies in multiple organs. It is defined by four main clinical findings: congenital lipomatous overgrowth, vascular malformations, epidermal nevi, and skeletal/spinal abnormalities. The presence of truncal overgrowth and characteristic patterned macrodactyly at birth differentiates CLOVE from other syndromic forms of overgrowth.[3] FunctionPK3CA_HUMAN Phosphoinositide-3-kinase (PI3K) that phosphorylates PtdIns (Phosphatidylinositol), PtdIns4P (Phosphatidylinositol 4-phosphate) and PtdIns(4,5)P2 (Phosphatidylinositol 4,5-bisphosphate) to generate phosphatidylinositol 3,4,5-trisphosphate (PIP3). PIP3 plays a key role by recruiting PH domain-containing proteins to the membrane, including AKT1 and PDPK1, activating signaling cascades involved in cell growth, survival, proliferation, motility and morphology. Participates in cellular signaling in response to various growth factors. Involved in the activation of AKT1 upon stimulation by receptor tyrosine kinases ligands such as EGF, insulin, IGF1, VEGFA and PDGF. Involved in signaling via insulin-receptor substrate (IRS) proteins. Essential in endothelial cell migration during vascular development through VEGFA signaling, possibly by regulating RhoA activity. Required for lymphatic vasculature development, possibly by binding to RAS and by activation by EGF and FGF2, but not by PDGF. Regulates invadopodia formation in breast cancer cells through the PDPK1-AKT1 pathway. Participates in cardiomyogenesis in embryonic stem cells through a AKT1 pathway. Participates in vasculogenesis in embryonic stem cells through PDK1 and protein kinase C pathway. Has also serine-protein kinase activity: phosphorylates PIK3R1 (p85alpha regulatory subunit), EIF4EBP1 and HRAS.[4] Publication Abstract from PubMedPI3Kalpha remains an attractive target for development of anticancer targeted therapy. A number of p110alpha crystal structures in complex with the nSH2-iSH2 fragment of p85 regulatory subunit have been reported, including a few small molecule co-crystal structures, but the utilization of this crystal form is limited by low diffraction resolution and a crystal packing artifact that partially blocks the ATP binding site. Taking advantage of recent data on the functional characterization of the lipid binding properties of p110alpha, we designed a set of novel constructs allowing production of isolated stable p110alpha subunit missing the Adapter Binding Domain (ABD) and lacking or featuring a modified C-terminal lipid binding motif. While this protein is not catalytically competent to phosphorylate its substrate PIP2, it retains ligand binding properties as indicated by direct binding studies with a pan-PI3Kalpha inhibitor. Additionally, we determined apo and PF-04691502 bound crystal structures of the p110alpha (105-1048) subunit at 2.65 A and 2.85 A respectively. Comparison of isolated p110alpha (105-1048) with the p110alpha /p85 complex reveals a high degree of structural similarity, which validates suitability of this catalytically inactive p110alpha for iterative SBDD. Importantly, this crystal form of p110alpha readily accommodates the binding of non-covalent inhibitor by means of a fully accessible ATP site. The strategy presented here can be also applied to structural studies of other members of PI3KIA family. Engineering of an isolated p110alpha subunit of PI3Kalpha permits crystallization and provides a platform for structure-based drug design.,Chen P, Deng YL, Bergqvist S, Falk M, Liu W, Timofeevski S, Brooun A Protein Sci. 2014 Jul 12. doi: 10.1002/pro.2517. PMID:25043846[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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