| Structural highlights
Disease
PK3CA_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]
Function
PK3CA_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 PubMed
We report two crystal structures of the wild-type phosphatidylinositol 3-kinase alpha (PI3Kalpha) heterodimer refined to 2.9 A and 3.4 A resolution: the first as the free enzyme, the second in complex with the lipid substrate, diC4-PIP(2), respectively. The first structure shows key interactions of the N-terminal SH2 domain (nSH2) and iSH2 with the activation loop that suggest a mechanism by which the enzyme is inhibited in its basal state. In the second structure, the lipid substrate binds in a positively charged pocket adjacent to the ATP-binding site, bordered by the P-loop, the activation loop and the iSH2 domain. An additional lipid-binding site was identified at the interface of the ABD, iSH2 and kinase domains. The ability of PI3Kalpha to bind an additional PIP(2) molecule was confirmed in vitro by fluorescence quenching experiments. The crystal structures reveal key differences in the way the nSH2 domain interacts with wild-type p110alpha and with the oncogenic mutant p110alphaH1047R. Increased buried surface area and two unique salt-bridges observed only in the wild-type structure suggest tighter inhibition in the wild-type PI3Kalpha than in the oncogenic mutant. These differences may be partially responsible for the increased basal lipid kinase activity and increased membrane binding of the oncogenic mutant.
Structural basis of nSH2 regulation and lipid binding in PI3Kalpha.,Miller MS, Schmidt-Kittler O, Bolduc DM, Brower ET, Chaves-Moreira D, Allaire M, Kinzler KW, Jennings IG, Thompson PE, Cole PA, Amzel LM, Vogelstein B, Gabelli SB Oncotarget. 2014 Jul 30;5(14):5198-208. PMID:25105564[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
See Also
References
- ↑ Lee JW, Soung YH, Kim SY, Lee HW, Park WS, Nam SW, Kim SH, Lee JY, Yoo NJ, Lee SH. PIK3CA gene is frequently mutated in breast carcinomas and hepatocellular carcinomas. Oncogene. 2005 Feb 17;24(8):1477-80. PMID:15608678 doi:10.1038/sj.onc.1208304
- ↑ Hafner C, Lopez-Knowles E, Luis NM, Toll A, Baselga E, Fernandez-Casado A, Hernandez S, Ribe A, Mentzel T, Stoehr R, Hofstaedter F, Landthaler M, Vogt T, Pujol RM, Hartmann A, Real FX. Oncogenic PIK3CA mutations occur in epidermal nevi and seborrheic keratoses with a characteristic mutation pattern. Proc Natl Acad Sci U S A. 2007 Aug 14;104(33):13450-4. Epub 2007 Aug 2. PMID:17673550 doi:10.1073/pnas.0705218104
- ↑ Kurek KC, Luks VL, Ayturk UM, Alomari AI, Fishman SJ, Spencer SA, Mulliken JB, Bowen ME, Yamamoto GL, Kozakewich HP, Warman ML. Somatic mosaic activating mutations in PIK3CA cause CLOVES syndrome. Am J Hum Genet. 2012 Jun 8;90(6):1108-15. doi: 10.1016/j.ajhg.2012.05.006. Epub, 2012 May 31. PMID:22658544 doi:10.1016/j.ajhg.2012.05.006
- ↑ Yamaguchi H, Yoshida S, Muroi E, Yoshida N, Kawamura M, Kouchi Z, Nakamura Y, Sakai R, Fukami K. Phosphoinositide 3-kinase signaling pathway mediated by p110alpha regulates invadopodia formation. J Cell Biol. 2011 Jun 27;193(7):1275-88. doi: 10.1083/jcb.201009126. PMID:21708979 doi:10.1083/jcb.201009126
- ↑ Miller MS, Schmidt-Kittler O, Bolduc DM, Brower ET, Chaves-Moreira D, Allaire M, Kinzler KW, Jennings IG, Thompson PE, Cole PA, Amzel LM, Vogelstein B, Gabelli SB. Structural basis of nSH2 regulation and lipid binding in PI3Kalpha. Oncotarget. 2014 Jul 30;5(14):5198-208. PMID:25105564
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