Abstract
AimsMutations in PIK3CA, which encodes p110α subunit of PI3K class IA enzymes, are highly frequent in breast cancer. Here, we aimed to probe mutations in exon 9 of PIK3CA and computationally simulate their function. Materials and methodsPCR/HRM and PCR/sequencing were used for mutation detection in 40 breast cancer specimens. The identified mutations were queried via in silico algorithms to check the pathogenicity. The molecular dynamics (MD) simulations were utilized to assess the function of mutant proteins. Key findingsThree samples were found to harbor at least one of the E542K, E545K and L551Q mutations of which L551Q has not been reported previously. All mutations were confirmed to be pathogenic and MD simulations revealed their impact on protein function and regulation. The novel L551Q mutant dynamics was similar to that of previously found carcinogenic mutants, E542K and E545K. A functional role for the helical domain was also suggested by which the inhibitory signal of p85α is conducted to kinase domain via helical domain. Helical domain mutations lead to impairment of kinase domain allosteric regulation. Interestingly, our results show that p110α substrate binding pocket of kinase domain in mutants may have differential affinity for enzyme substrates, including anit-p110α drugs. SignificanceThe novel p110α L551Q mutation could have carcinogenic feature similar to previously known helical domain mutations.
Highlights
Background Mutations inPIK3CA, which encodes p110 subunit of Phosphatidylinositol 3 kinase (PI3K) class IA enzyme, are highly frequent in breast cancer
Initial screening via PCR/High Resolution Melting (HRM) was performed on DNA extracted from 40 tumor samples and the HRM positive samples were subsequently investigated by Sanger sequencingfor mutations on exon 9
E542K and E545Kvariants were previously reported as pathogenic mutations in My Cancer Genome[21], cosmic[20] and The Cancer Genome Atlas (TCGA) [22]; L551Q mutation did not exist in any of the cancer databases
Summary
Background Mutations inPIK3CA, which encodes p110 subunit of PI3K class IA enzyme, are highly frequent in breast cancer. Among the members of class IA, p110α and p85α are expressed in most cells, encoded by PIK3CA and PIK3R1 genes, respectively [5] Large genomic studies such as The Cancer Genome Atlas (TCGA) have revealed that PIK3CA is the most frequently mutated gene in breast cancer [6, 7]. This data shows that ~40% of all breast tumors have at least one PIK3CA mutation that could be a representation of PI3K oncogenic pathway.The majority of hotspot gain-of-function PIK3CA mutations are clustered in exon 9 and 20 of the gene that correspond to the helical and kinase domains of p110α, respectively[8]. A recent study [11]has suggested that p85α allosterically regulates p110α kinase activity via helical domain.Generally this change makes hyper-activation of PI3Kα followed by overexpression of AKT leading to an uncontrolled cell division[9, 12]
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