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Phosphatidylinositol 3-kinase binds to alpha-actinin through the p85 subunit.

ABSTRACT: Phosphatidylinositol 3-kinase (PI 3-kinase) has been shown to play an important role in the signal transduction of cell growth. It is also suggested that it is involved in cytoskeletal reorganization. We have found that alpha-actinin copurifies with PI 3-kinase from bovine thymus. The antibody against PI 3-kinase 85 kDa subunit (p85) also co-immunoprecipitates alpha-actinin from lysates of NIH/3T3 cells. In addition, anti-alpha-actinin antibody coprecipitates PI 3-kinase activity. This coprecipitation was observed even after depolymerization of actin fibres, suggesting that PI 3-kinase binds directly to alpha-actinin. As alpha-actinin is a phosphatidylinositol 4,5-bisphosphate (PI4,5P2)-binding protein, binding experiments using various constructs of truncated p85 were carried out in the presence or absence of PI4,5P2. In the absence of PI4,5P2, chicken gizzard alpha-actinin binds only to the whole p85 construct, but it binds to the proline-rich region of p85 fragments in the presence of PI4,5P2. This binding is enhanced with increased concentrations of Pi4,5P2 up to 10 microM, whereas phosphatidylinositol and phosphatidylinositol 4-phosphate were not good activators of alpha-actinin binding. These results suggest that PI 3-kinase binds to alpha-actinin and regulates cytoskeletal reorganization.

SUBMITTER: Shibasaki F

PROVIDER: S-EPMC1137263 | biostudies-other | 1994 Sep

REPOSITORIES: biostudies-other

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Project description:Bronchopulmonary neuroendocrine tumours (BP-NETs) comprise a large spectrum of tumours including typical carcinoids (TCs), atypical carcinoids (ACs), large-cell neuroendocrine carcinomas (LCNECs) and small-cell lung carcinomas (SCLCs) that exhibit considerably different biological aggressiveness and clinical behaviours. The phosphatidylinositol-3-kinase α catalytic subunit (PIK3CA) gene is known to be involved in the pathogenesis of several types of human cancers through gene amplification, deletions or somatic missense mutations within the helical and catalytic domains. However, the PIK3CA gene status in BP-NETs has yet to be explored. This study aimed to investigate the PIK3CA gene status in a large series of BP-NETs by direct gene sequencing and to analyse its correlation with the main clinicopathological parameters. To the best of our knowledge, we demonstrated for the first time a high frequency of somatic missense mutations (23.2%) in the PIK3CA gene in a series of 190 BP-NETs, including 75 TCs, 23 ACs, 17 LCNECs and 75 SCLCs. The frequency of the PIK3CA gene mutation in the kinase domain was higher (17.9%) than that in the helical domain (5.3%). When the mutational status of the PIK3CA gene was compared with the main clinical and pathological characteristics of the BP-NET patients, we found a significant association between PIK3CA gene mutations and BP-NET histology (p=0.011). Interestingly, the frequency of PIK3CA gene mutations increased with the biological aggressiveness of all BP-NETs, except LCNECs. In conclusion, our results suggest that PIK3CA gene mutations may play a key role in tumourigenesis and aggressiveness of BP-NETs. The PIK3CA gene may represent a favourable candidate for an effective therapeutic strategy in the treatment of patients with BP-NETs.

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Phosphatidylinositol 3-kinase binds to alpha-actinin through the p85 subunit.

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